Printed by H. Howard, RA.         Engraved by W. T. Fry.



William Kirby. M.A. F.R. L.S. &c

Published by Longman & C^o. London, July, 1825.

[Pg i]

AN

INTRODUCTION

TO

ENTOMOLOGY:

OR

ELEMENTS

OF THE

NATURAL HISTORY OF INSECTS:

WITH PLATES.

By WILLIAM KIRBY, M.A. F.R. and L.S.

RECTOR OF BARHAM,
AND

WILLIAM SPENCE, Esq. F.L.S.

VOL. III.

LONDON:

PRINTED FOR

LONGMAN, REES, ORME, BROWN, AND GREEN,

PATERNOSTER ROW.

1826.

[Pg ii]

PRINTED BY RICHARD TAYLOR,
SHOE LANE, LONDON.

[Pg iii]

ADVERTISEMENT.

The publication of the concluding volumes of the "Introduction to Entomology" has been unavoidably delayed by the continued ill health of one of the Authors, which has devolved upon the other a considerable increase of labour, and demanded a greater expenditure of time than would otherwise have been required: for though Mr. Spence put every facility in Mr. Kirby's power, and had drawn up a rough copy of every Letter belonging to his department; yet, as most of them had been written several years ago, many curious facts, and a great variety of interesting information subsequently derived from various sources, were necessarily to be inserted, and the whole to be prepared for the press.

When the thousands of objects that were to be examined, and many of them repeatedly, in composing the Letters on the External Anatomy of Insects, are considered, it will not appear surprising[Pg iv] if some errors should have crept in; especially as Mr. Kirby was deprived of the effectual help formerly derived from the acumen, learning, and judgement of his esteemed coadjutor, by his lamented and protracted indisposition: but it is hoped that these errors will be found of minor importance, and not to affect any general principles advanced. The same remarks are also in part applicable to the Anatomical and Orismological Tables (Vol. III. p. 354-393, and Vol. IV. p. 257-354), which were drawn up by the Authors jointly many years ago, before any other portion of the work was composed, but which have, especially the former, required considerable alterations and additions in consequence of subsequent observations and information.

It will not be amiss here to state, in order to obviate any charge of inconsistency in the possible event of Mr. Kirby's adverting in any other work to this subject, that though on every material point the authors have agreed in opinion, their views of the theory of instinct do not precisely accord. That given in the second and fourth volumes is from the pen of Mr. Spence.

It was originally intended, as mentioned in the Preface, to have given a complete list of Entomological[Pg v] works, of which a large portion was drawn up; but the great length to which more important matters have extended, has rendered necessary the intire omission of this list,—an omission in some degree compensated by the catalogue of Authors quoted, which comprises most of the standard Entomological works.

[Pg vi]

ERRATA.

DIRECTIONS TO THE BINDER.

The Synoptical Table of the Nomenclature of the Parts of the External Crust of Insects should be placed opposite to page 354.

Plates VI-XX. should be placed in this Volume, and the remainder in the Fourth.

It is however suggested to Purchasers, that in binding complete Sets of the Work, a separate Volume may be formed of the Synoptical Table, the Plates and their Explanations, and the Indexes.

[Pg vii]

CONTENTS OF VOL. III.

[Pg viii]

NOTICE RESPECTING VOL. I. and II.

It being judged expedient, since the publication of the last Edition of the first and second Volumes of this Work, to adopt a new plan with respect to the reference letters of the Plates, the Reader is requested to make the following corrections in those Volumes.

[Pg 1]

AN INTRODUCTION TO ENTOMOLOGY.

LETTER XXVIII.

DEFINITION OF THE TERM INSECT.

What is an insect? This may seem a strange question after such copious details as have been given in my former Letters of their history and economy, in which it appears to have been taken for granted that you can answer this question. Yet in the scientific road which you are now about to enter, to be able to define these creatures technically is an important first step which calls for attention. You know already that a butterfly is an insect—that a fly, a beetle, a grasshopper, a bug, a bee, a louse, and flea, are insects—that a spider also and centipede go under that name; and this knowledge, which every child likewise possesses, was sufficient for comprehending the subjects upon which I have hitherto written. But now that we are about to take a nearer view of them—to investigate their anatomical and physiological characters[Pg 2] more closely—these vague and popular ideas are insufficient. In common language, not only the tribes above mentioned, but most small animals—as worms, slugs, leeches, and many similar creatures, are known by the name of insects. Such latitude, however, cannot be admitted in a scientific view of the subject, in which the class of insects is distinguished from these animals just as strictly as beasts from birds, and birds from reptiles and amphibia, and these again from fishes. Not, indeed, that the just limits of the class have always been clearly understood and marked out. Even when our correspondence first commenced, animals were regarded as belonging to it, which since their internal organization has been more fully explained, are properly separated from it. But it is now agreed on all hands, that an earthworm, a leech, or a slug, is not an insect; and a Naturalist seems almost as much inclined to smile at those who confound them, as Captain Cook at the islanders who confessed their entire ignorance of the nature of cows and horses, but gave him to understand that they knew his sheep and goats to be birds.

You will better comprehend the subsequent definition of the term Insect, after attending to a slight sketch of the chief classifications of the animal kingdom, more especially of the creatures in question, that have been proposed. That of Aristotle stands first. He divides animals into two grand sections, corresponding with the Vertebrata and Invertebrata of modern Zoologists: those, namely, that have blood, and those that have it not[1]:—by this it appears that he only regarded red blood as real blood; and probably did not suspect that there was[Pg 3] a true circulation in his Mollusca and other white-blooded animals. His Enaima, or animals that have blood, he divides into Quadrupeds, Birds, Fishes, Cetacea, and Apods or reptiles; though he includes the latter, where they have four legs, amongst the quadrupeds[2]; and his Anaima, or animals without blood, into Malachia, Malacostraca, Ostracoderma, and Entoma. The first of these, the Malachia, he defines as animals that are externally fleshy and internally solid, like the Enaima; and he gives the Sepia as the type of this class, which answers to the Cephalopoda of the moderns. The next, the Malacostraca, synonymous with the Crustacea of Cuvier and Lamarck, are those, he says, which have their solid part without and the fleshy within, and whose shell will not break, but splits, upon collision[3]. The Ostracoderma, corresponding with the Testacea of Linné, he also defines as having their fleshy substance within, and the solid without; but whose shell, as to its fracture, reverses the character of the Malacostraca. He defines his last class Entoma, in Latin Insecta, with which we are principally concerned, as animals whose body is distinguished by incisures, either on its upper or under side, or on both, and has no solid or fleshy substance separate, but something intermediate, their body being equally hard both within and without[4]. This definition would include the Annelida and most other Vermes of Linné, except the Testacea, which accordingly were considered as insects by those Zoologists that intervened between Aristotle and the latter author. The Stagyrite, however, in another place,[Pg 4] has expressly excluded all apods[5]. From other passages in his works, it appears that he regarded the Vermes, &c. either as larvæ, or as produced spontaneously and not ex ovo[6].

This definition of an insect, though partly founded on misconception, as well as his primary division of animals in general, is by no means contemptible. If you look at a bee or a fly, you will observe at first sight that its body is insected, being divided as it were into three principal pieces—head, trunk, and abdomen[7]; and if you examine it more narrowly, you will find that the two last of these parts, especially the abdomen, are further subdivided. And this character of insection, or division into segments, more or less present in almost every insect[8], is not to be found (with the exception of the Crustacea, which Aristotle[Pg 5] distinguishes by the nature of their integument and its contents) in any of the other classes into which he divided animals without blood. It was on account of this most obvious of their characters, that these little creatures were in Greek named Entoma, and in Latin Insecta; and from the former word, as you know, our favourite science takes the name of Entomology.

Pliny adhering to the definition of Aristotle, as far as it relates to the insection of the animals we are speaking of, expressly includes Apods, as well as Aptera, amongst them[9]; and in this was followed, without any attempt at improvement, by all the entomological writers that intervened between him and the great Aristotle of the moderns, Linné.

This illustrious naturalist, aware of the incorrectness of the primary divisions of the animal kingdom founded upon the presence or absence of blood, establishes his system upon the structure of the heart, and upon the temperature and colour of the circulating fluid. He divided animals into two great sections or sub-kingdoms, each comprising two classes. His first section included those having a heart with two ventricles, two auricles, and warm and red blood, viz. the Mammalia or beasts, and the Aves or birds. His second, those having a heart with one ventricle, one auricle, and cold and red blood, namely, the classes Amphibia, which included reptiles, serpents, &c. and Pisces or fish. His third, those having a heart with one ventricle and no auricle, and cold white sanies in the place of blood, namely, his classes Insecta et Vermes, including the Invertebrate animals of Lamarck.[Pg 6] Thus the first of Aristotle's great divisions he increased by the addition of a new and very distinct class, the Amphibia, by which some ground was gained in the science; but as much was lost by his compressing the four classes of which the last consisted into two, by which the natural classes of Cephalopoda and Crustacea merged under Insecta and Vermes. Linné was not aware of the extraordinary fact, that the Cephalopoda have three hearts; and that though the Crustacea and Arachnida have a circulation, Insects have none, or he would never have taken this retrograde step.

Indeed Linné's definition of an Insect is, in many most material points, inapplicable, not only to the Crustacea, but to many other animals included under that denomination. This will appear evident from a very slight examination. Thus it runs: "Polypod animalcula, breathing by lateral spiracles, armed every where with an osseous skin, whose head is furnished with movable sensitive antennæ[10]." Now of this definition only the first member can be applied to the whole class which it is meant to designate; for the entire genus Cancer L., which, with some others, forms the class Crustacea of the moderns, does not respire by spiracles at all, but by gills; and the same in some degree may be said of spiders, scorpions, &c. With the last member of the definition Linné himself must have been aware that a large number of what he conceived to be insects were at variance, as mites, spiders, and many other of his apterous tribes: though from some very recent observations of M.[Pg 7] Latreille[11], there seems some ground for thinking, that in these the antennæ are represented by the mandibles, palpi, &c.[12], and to the soft flexible, coriaceous or membranous skin of a vast number of insects, the term cutis ossea is by no means applicable.

Evident as these incongruities are, when the Herculean task which Linné imposed upon himself, and the vastness and variety of his labours, are considered, they become very venial. Indeed, unless he had divided his class Insecta into two or more, it was impossible to define it intelligibly to ordinary readers, otherwise than nearly in the terms which he actually employed; and these characters, restricted and amended by qualifying clauses, are still those to which recurrence must be had in a popular definition of the class, when separated as it ought to be from the Crustacea and Arachnida.

Pennant, Brisson, and other zoologists, who, attending to nature rather than system, saw the impropriety of uniting a crab or a lobster in the same class with a bee or a beetle, long since assigned the Crustacea their ancient distinct rank. "But these changes," as Latreille observes[13], "being only founded upon external characters, might be deemed arbitrary; and to fix our opinion, it was necessary to have recourse to a decisive authority—the internal and comparative organization of these animals.[Pg 8]" It results from the observations of the most profound comparative anatomist of our age, M. Cuvier, that the Crustacea and Arachnida differ from insects properly so called, and particularly from those that are furnished with wings, in having a complete system of circulation, a different mode of respiration, and that they have a more perfect organization. Influenced by these motives, both Cuvier and Lamarck have considered them as forming two classes separate from insects. Treviranus, led by considerations founded on the organs of circulation, of respiration, and of generation, is of opinion that spiders and scorpions ought to form one class with the Crustacea: he observes, however, that the nervous system of all three is very dissimilar; and that in an arrangement founded on this circumstance, the organs of motion, and the external shape, even spiders and scorpions must be placed in different classes[14].

It is to be observed with regard to the Arachnida of the French school, that the class as laid down by them includes several animals that have no circulation, and breathe by tracheæ, of which description are the mites (Acarus L.), and the harvest-men (Phalangium L.) &c.; and therefore it has been divided into two orders, Pulmonaria and Tracheana; but if the definition from the internal organization be adhered to, the latter should either remain with the class Insecta, or form a new one by themselves. Yet the animals that compose the Trachean order of Arachnida, their external form considered, are certainly much more nearly related to the spiders and[Pg 9] scorpions than to any members of the class Insecta at present known. This circumstance, perhaps, may seem to throw some doubt upon the modern system of classification.

I must further observe, that the assertion of Treviranus, which appears to intimate that the respiration of the pulmonary Arachnida is the same with that of the Crustacea, is not quite correct, since in the latter the branchiæ or gills are external, and in the former internal, the air entering by spiracles before it acts upon them[15].

It may not be amiss in this place to lay before you the principal points in which the Crustacea and Arachnida agree with Insecta, and also those in which they differ.

The Crustacea agree with Insecta in having a body divided into segments, furnished with jointed legs, compound eyes, and antennæ. Their nervous system also is not materially different, and they are both oviparous. They differ from them in having the greater insections of the body less strongly marked; in the greater number of legs on the trunk, the anterior ones performing the office of maxillæ: in their eyes usually on a moveable footstalk: their palpigerous mandibles; and their four antennæ at least in the great majority. But the principal difference consists in the internal organization and the fountains of vitality; for the Crustacea have a double circulation, the fountain of which is a heart in the middle of their thorax[16]. They have too a kind of gizzard and liver, at least the Decapods[17], and their respiration is by gills. Genuine insects terminate their[Pg 10] existence after they have laid their eggs[18]; but the Crustacea live longer, and lay more than once.

The Arachnida will be found to differ from insects more widely than even the Crustacea. They agree in their jointed legs and palpi; immoveable eyes; and in being covered with a coriaceous or corneous integument: but they differ in having a system of circulation; gills instead of tracheæ; their organs of generation double; and the females lay more than once in their lives. Their head also is not distinct from the trunk as in insects; they have no compound eyes; and their antennæ, if we admit the opinion on this head of MM. Latreille and Treviranus, that they have representatives of these organs, differ totally in structure, situation, and use, from those of the great body of insects. In the Araneidæ or Spiders, their body seems to have no segments or incisure but that which separates the abdomen from the trunk; and in the Scorpionidæ they are observable only in the abdomen. Other particulars might be enumerated in which these two classes differ from insects; but these will be sufficient to convince you that Aristotle and MM. Cuvier and Lamarck were justified in separating them.

The two last-mentioned authors made further improvements in Zoology. The latter, from the consideration of the general structure of animals, perceiving that Aristotle's Enaima were distinguished from his Anaima, by being built as it were upon a vertebral column, very judiciously changed the denomination, which was indeed improper, of "The Philosopher's" two sub-kingdoms, into[Pg 11] that of Vertebrata or animals that have a vertebral column, and Invertebrata or those that have no vertebral column. These he distributes into three primary divisions according to their supposed degrees of intelligence—Thus:

Profiting by the light afforded by the Aristotelian system, this eminent zoologist improved, we see, upon that of Linné, by resolving his Insecta into three classes, and his Vermes into seven, interposing the Linnean Insecta between the four first and three last, in which he was not so happy, since as to sense insects should certainly occupy the place he has here assigned to the Mollusca.

In the work from which I have taken this statement of Lamarck's system, that acute writer has given a sketch of another method of arrangement, in which he has made the first deviation from the beaten track of an unbroken[Pg 12] and unbranching series. In the Supplement to the first volume, he has distributed the Invertebrata in a double subramose series—one consisting of articulate, and the other of inarticulate animals[20].

Upon Lamarck's system, most of the modern ones, with some variation, are founded. There is one, however, by a learned countryman of ours, that is more unique, sui generis, and I may add profound, than any that has yet appeared. I am speaking of that, you will perceive, of which our friend Mr. Wm. MacLeay has given a detailed statement in his Horæ Entomologicæ. In this he goes even far beyond what Lamarck has attempted in the above sketch, and substantiates his claim to be considered as one of those original thinkers, rari nantes in gurgite vasto, that do not appear every day. The following are the principal bases of his system.

1. That all natural groups, whether kingdoms or any subdivision of them, return into themselves; a distribution which he expresses by circles.

2. That each of these circles is formed precisely of five groups, each of which is resolvable into five other smaller groups, and so on till you reach the extreme term of such division.

3. That proximate circles or larger groups are connected by the intervention of lesser groups, which he denominates osculant.

4. That there are relations of analogy between the corresponding points of contiguous circles.

This system he has represented by tables of circles inscribed with the five primary divisions of each group. His first table exhibits a general view of organized matter[Pg 13] as distributed in the animal and vegetable kingdoms—Thus:

Our learned author here divides the animal kingdom into what may be denominated five sub-kingdoms or provinces, in three of which (with the exception of the Crustacea and Arachnida belonging to his Annulosa) no circulation of blood is visible, but which obtains in the rest. These he names—

1. Acrita, consisting of the Infusory Animals, the Polypi, the Corallines, the Tæniæ, and the least organized of the Intestinal Worms.

2. Radiata, including the Jelly-fish, Star-fish, Echini, and some others.

3. Annulosa, consisting of Insecta, Arachnida, and Crustacea.

4. Vertebrata, consisting of Beasts, Birds, Reptiles, Amphibia, and Fishes.

5. Mollusca, including the numerous tribes of shell-fish, land-shells, slugs, &c., which, from their mucous or gelatinous substance, from their nervous system and the imperfection of their senses, return again to the Acrita,[Pg 14] though connected with the Vertebrata by having a heart and circulation.

His next set of circles shows the sub-division of these five sub-kingdoms into classes—Thus:

In this scheme the osculant classes are those placed between the circles. In the Mollusca circle two classes are still wanting to complete the quinary arrangement of that sub-kingdom. I am not sufficiently conversant[Pg 15] with the details of the animal kingdom at large to hazard any decided opinion upon Mr. MacLeay's whole system, or to ascertain whether all these classes are sufficiently distinct[21]. My sentiments with regard to those of the Annulosa I shall state to you hereafter.

Upon a future occasion I shall consider more at large the station to which insects seem entitled in a system of invertebrate animals, which will not accord exactly with that assigned by MM. Cuvier and Lamarck. But I am now in a field in which I have no intention to expatiate further, than as it is connected with the subject of the present letter. I shall therefore confine myself in what I have more to say to the definitions of Insecta that have been given by modern authors, beginning with that of the zoologist last mentioned. Insects form a part of his second group, which he terms sensitive animals (animaux sensibles), which group he thus defines: "They are sentient, but obtain from their sensations only perceptions of objects—a kind of simple ideas which they cannot combine to obtain complex ones. Charact. No vertebral column; a brain, and most commonly an elongated medullary mass; some distinct senses; the organs of movement attached under the skin: form symmetrical, by parts, in pairs[22]." This division of animals, from the[Pg 16] kind and degree of sense and intelligence that they possess, seems rather fanciful than founded in nature, since many insects show a greater portion of them than many vertebrate animals. Compare in this respect a bee with a tortoise[23]. Lamarck divides his group of animaux sensibles into two sections, namely, Articulated animals, exhibiting segments or articulations in all or some of their parts; and Inarticulatcd animals, exhibiting neither segments nor articulations in any of their parts. Insecta, Arachnida, and Crustacea, belong to the first of these sections, which he defines as "those whose body is divided into segments, and which are furnished with jointed legs bent at the articulations[24]." Insecta he defines—"Articulate animals, undergoing various metamorphoses, or acquiring new kinds of parts—having, in their perfect state, six feet, two antennæ, two compound eyes, and a corneous skin. The majority acquiring wings. Respiration by spiracles (stigmates), and two vascular opposite chords, divided by plexus, and constituting aeriferous tracheæ, which extend every where. A small brain at the anterior extremity of a longitudinal knotty marrow, with nerves. No system of circulation, no conglomerate glands. Generation oviparous: two distinct sexes. A single sexual union in the whole course of life[25]." Arachnida he defines—"Oviparous animals, having at all times jointed legs, undergoing no metamorphosis, and never acquiring new kinds of parts. Respiration tracheal or branchial: the openings for the entrance of the air spiraculiform (stigmatiformes). A heart and circulation beginning in[Pg 17] many. The majority couple often in the course of life[26]." I shall next add his definition of Crustacea: "Oviparous, articulated, apterous animals, with a crustaceous integument more or less solid, having jointed legs; eyes either pedunculate or sessile, and most commonly four antennæ, with a maxilliferous mouth seldom rostriform; maxillæ in many pairs placed one over the other; scarcely any under-lip; no spiraculiform openings for respiration; five or seven pair of legs; a longitudinal knotty marrow terminated anteriorly by a small brain. A heart and vessels for circulation. Respiration branchial with external branchiæ, sometimes hid under the sides of the shell of the thorax, or shut in prominent parts; sometimes uncovered, and in general adhering to particular legs or to the tail. Each sex usually double[27]."

I have given Lamarck's definitions of these three classes, all considered as Insecta by Linné, that by comparing them together you may be better enabled to appreciate the system of this author. On looking over the characters of the Arachnida as here given, you will see at once that it consists of heterogeneous animals—for in fact he includes in this class not only the Trachean Arachnida of Latreille, but the Ametabolia of Dr. Leach, or the Hexapod Aptera, and the Myriapoda.

I shall next copy for you Latreille's latest definition of Insecta and Arachnida.

"Insecta: A single dorsal vessel representing the heart: two trunks of tracheæ running the whole length of the body, and opening externally by numerous spiracles; two antennæ; very often upper appendages for flight, indicating the metamorphosis to which the animal[Pg 18] is subject when young; legs most commonly reduced to six. Arachnida: Distinguished from Crustacea by having their respiratory organs always internal, opening on the sides of the abdomen or thorax to receive the respirable fluid. Sometimes these organs perform the office of lungs, and then the circulation takes place by means of a dorsal vessel, which sends forth arterial, and receives venose branches. Sometimes they are tracheæ or air-vessels, which, as in the class Insecta, replace those of circulation. These have only the vestige of a heart, or a dorsal vessel alternately contracting and sending forth no branch. The absence of antennæ, the reunion of the head with the thorax, a simple trachea but ramified and almost radiating, serve to distinguish these last Arachnida, or the most imperfect of insects, which respire only by tracheæ[28]." Under this head he observes—"Of all these characters, the most easy to seize and the most certain would doubtless be, if there were no mistake in it, that of the absence of antennæ; but later and comparative researches, confirmed by analogy, have convinced me, that these organs, under particular modifications it is true, and which have misled the attention of naturalists, do exist[29]:" and he supposes, from the situation and direction of the mandibles of the Arachnida, corresponding with that of the intermediate pair of antennæ in Crustacea, that they really represent the latter organs. If this supposition be admitted, their use is wholly changed; the palpi, in fact, executing the functions of antennæ, which probably induced Treviranus to call them Fühlhörner (Feelinghorns).[Pg 19] Perhaps these last may be regarded as in some sort representing the external antennæ of the Crustacea? With regard to Insecta, their antennæ seem to disappear in the Pupiparæ Latr., or the genus Hippobosca L.

The above definitions of the Arachnida by these two celebrated authors, appear to me the reverse of satisfactory. When we are told of animals included in it, that some breathe by gills and others by tracheæ, that some have a heart and circulation and others not, we are immediately struck by the incongruity, and are led to suspect that animals differing so widely in the fountains of life ought not to be associated in the same class. A learned zoologist of our own country, Dr. Leach, seems to have made a nearer approach to a classification in accordance with the internal organization, by excluding from Arachnida the Acari and Myriapoda.

Sub-kingdom Annulata Cuv.

Mr. MacLeay, on whose system I shall now say a few words, divides his sub-kingdom Annulosa into five classes, namely, Crustacea, Ametabola, Mandibulata, Haustellata, Arachnida. From the Crustacea he goes by the genus[Pg 20] Porcellio Latr. to Iulus[31], which begins his Ametabola: these he connects with the Mandibulata, by Nirmus, which he thinks approaches some of the corticarious Coleoptera[32]. This class he appears to leave by the Trichoptera Kirby, and so enters his Haustellata by the Lepidoptera[33], and leaves it again by the Diptera by means of the Pupiparæ Latr., especially Nycteribia, connecting this class with the Arachnida, which he enters by the Hexapod Acari L.[34], and these last he appears to leave by the Araneidæ, and to enter the Crustacea by the Decapods[35]: thus making good his circle of classes, or a series of Annulose animals returning into itself. Mr. MacLeay's whole system upon paper appears very harmonious and consistent, and bears a most seducing aspect of verisimilitude; but it has not yet been so thoroughly weighed, discussed, and sifted, as to justify our adopting it in toto at present: should it, however, upon an impartial and thorough investigation, come forth from the furnace as gold, and be found to correspond with the actual state of things in nature, my objections, which rest only upon some parts of his arrangement of Annulosa, would soon vanish. Some of those objections I will state here, and some will come in better when I treat of the Systems of Entomology. My first objection is, that his Ametabola, Mandibulata, and Haustellata, approach much nearer to each other than they do to the other two classes of his circle, or than even these last to each other; so that under this view it should primarily consist of three greater groups, resolvable, it may be, into five smaller ones. My next objection is, that he has also considered[Pg 21] the Trachean and Pulmonary Arachnida as forming one class. Whether an animal breathes by gills or tracheæ, or has a circulation or not, is surely as strong a reason for considering those so distinguished as belonging to different classes, as the taking of their food by suction or by manducation is, for separating others to the full as much or more nearly related as to their external structure. But of this more hereafter. I cannot help, as a last objection, lamenting that our learned author has rejected from his system a term consecrated from the most remote antiquity, and which, even admitting his arrangement, might have been substituted for Annulosa, a name borrowed by Scaliger from Albertus Magnus, neither of whom, in Entomology, is an authority to weigh against Aristotle, from whom we derive the term Insecta, in Greek Εντομα.

As Fabricius did not alter Linné's class Insecta, but merely broke up his orders into new ones, which he named classes, I shall give you a detail of the alterations he introduced into the science in a future letter.

Having stated what my predecessors have done in classification, I shall next proceed to lay before you my own sentiments as to—What is an insect. Since our correspondence commenced, the Arachnida, principally on account of their internal organization, have been excluded from bearing that name, carrying with them, as we have seen, several tribes, which as yet have not been discovered to differ materially in that respect from the present Insecta: for the sake, therefore, of convenience and consistency, that I may, as far as the case will admit, adhere to the Horatian maxim

[Pg 22]

I shall regard as Insects all those Annulosa that respire by tracheæ[36] and have no circulation, considering the Trachean Arachnida and the Myriapoda for the present as sub-classes, the one bordering upon the Arachnida, and the other upon the Crustacea. Some of these I am ready to own seem separated by an interval sufficiently wide from the Hexapods, which may be regarded as more peculiarly entitled to the denomination of Insects. The most striking differences will be found in the coalition of the head with the trunk in some (Phalangidæ), and the disappearance of the annulose form of the body in others (Acarus L.), so that the legs only are jointed[37]. Yet an[Pg 23] approach to such structure may be traced in some Hexapods; for instance, the coalition of the head and trunk in Melophagus, Latr., and that of the trunk and abdomen in Sminthurus, Latr.[38] The Myriapoda exhibit other remarkable differences; though their head and trunk are distinct, the former antenniferous, and their body annulose, the abdomen as well as the trunk is furnished with legs, sometimes amounting to hundreds; but even to this a tendency has been observed in some Hexapods[39]. If you examine a specimen of Machilis polypoda, an insect related to the common sugar-louse (Lepisma saccharina), you will find that the abdomen is furnished with a double series of elastic appendages, which, being instruments of motion, may be regarded as representing legs. It is worthy of notice, that the Myriapoda when first disclosed from the egg have never more than six legs[40], and keep acquiring additional pairs of them and additional segments to their abdomen as they change their skins: and it is equally remarkable, that many Hexapods are subject to a law in some degree the very reverse of this, having many abdominal legs in their first state, and losing them all in their last. The union of the head with the trunk in the Trachean Arachnida has been regarded as almost an unanswerable argument, in spite of their different internal organization, for including them in the same class with the Pulmonary Arachnida; but the case of Galeodes, which, though furnished with gills, (as an eminent Russian Entomologist Dr. G. Fischer is reported to have discovered,) implying also a circulation, and evidently belonging to the last-mentioned class, has nevertheless a distinct thorax consisting of more than one piece, to which[Pg 24] are affixed only six legs[41], proves that even this circumstance possesses no weight when set against the organization. If it was a difference in this respect, that proved the Crustacea classically distinct from Insecta—that likewise was the principal reason for the separation also of the Arachnida—it seems to follow that it ought also to furnish an argument equally cogent for considering the Trachean Arachnida, as well as the Myriapoda, distinct from the Pulmonary.

Another difference between the tribes in question is that of their metamorphosis; and this appears to have had great weight with Lamarck, inducing him to include in his Arachnida, not only the Tracheans and Myriapods, but even the apterous Hexapods, except Pulex, or the Anoplura and Thysanura of modern authors. But the metamorphosis alone, unless supported by the internal organization, will I think scarcely be deemed a sufficient reason for separating from each other tribes agreeing in that respect, and placing them with others with which they disagree. The metamorphosis in some of the Hexapods (Lepidoptera) consists in the loss of legs, the acquisition of wings, a great change in the oral organs and in the general form; in others (some Coleoptera), in the acquisition only of wings and a change of shape, the oral organs remaining much the same; in others again (Curculio L.), in the acquisition of six legs and wings and a change of form; in the flea, in the acquisition of six legs and a change of form only; in the Orthoptera, Hemiptera, &c. in the mere acquisition of wings; in the Libellulidæ, in the loss of the mask that covers the mouth and the acquisition of wings; in the Diptera, in the[Pg 25] acquisition of six legs, wings, a change of the oral organs and of the form; in some of the Octopods (Acarus L.), in the acquisition of a pair of legs; and in others (Phalangium and Aranea L.), solely in a modification of them as to their proportions; in the Myriapods, the alteration that takes place in this respect is considerable; a large number of pairs of legs is acquired and many additional abdominal segments, and the proportion which the abdomen bears to the whole insect is quite altered. In all these cases there is a change more or less, either partial or general, of the original shape or organs of the animal; and with regard to their metamorphosis, there is a greater difference between a young and adult Iulus than between a young and adult grasshopper or bug: so that if the metamorphosis, per se, be assumed as a principal regulator of the class, the grasshopper or bug have as little claim to belong to it as the Iulus.

M. Lamarck lays considerable stress upon another character—That Insecta engender only once in the course of their lives, and Arachnida more than once. But this, if examined, will be found to be confined chiefly to the Pulmonary Arachnida, the Tracheans following the law of Insecta in this respect[42].

You may perhaps object that the bringing of the Trachean Arachnida and the Myriapoda into the class Insecta will render the approximation of them to a natural arrangement more difficult, since it will be impossible at the same time to connect the Myriapods with the Crustacea, and the Trachean with the genuine Arachnida.[Pg 26] I admit the validity of your objection, but by no arrangement of insects in a simple series can we attain this object: the difficulty, however, may perhaps be obviated in this way. The distribution of organized matter, to adopt Mr. Wm. MacLeay's metaphor[43], begins in a dichotomy, constituting the animal and vegetable branches of the great tree of nature, and from these two great branches, by means of infinite ramifications, the whole system is formed, and, what is remarkable, these branches unite again so as to represent a series returning into itself, a discovery due to the patient investigation and acumen of our learned friend just mentioned. Now, in considering the Aptera order, we find at first setting out from the Hexapods, a dichotomy, where the Anoplura Leach branch off on the one side, and the Thysanura Latr. on the other—the former, by means of the Pediculidæ, taking their food by suction, particularly Phthirus Leach, or the Morpion (in which the segments of the trunk and abdomen become indistinct[44]) approach the Octopods by the hexapod Acari L.—the latter by Machilis polypoda tending towards the Myriapods. In the Octopod branch a further dichotomy takes place, from which you proceed on one side to the Araneidæ in the Arachnida, by Phalangium, &c.; and in the other by Chelifer, &c. to Scorpio. Again, the Myriapod branch also divides, going by the Iulidæ to one branch of the Isopod Crustacea, and by the Scolopendridæ to another.

But there is another view of this subject before alluded to, which may be repeated here, and which seems to[Pg 27] prove that the types of form in one natural group or class are reproduced in another; this appears to result from the following parallel series:

No type representing the Myriapoda has yet been discovered in the Arachnida class; but I have little doubt of its existence. You will observe that the analogies between the larvæ of the winged orders and the Aptera were first noticed by Mr. W. MacLeay[45]. It is probable that these parallel series of representatives of each other might be increased, as well as the numbers in the respective columns.

What I have said will, I trust, sufficiently justify me for making at present no more material alterations in the classification I long since proposed to you[46]; I shall, therefore, now proceed to define the objects I consider as Insecta; but I shall first observe—that as Latreille considers the branchiopod Crustacea or Entomostraca of Müller as entitled to the denomination of Crustaceo-Arachnida[47]; so his Trachean Arachnida might be called Arachnida-Insecta, and his Myriapoda, Crustaceo-Insecta.

[Pg 28]

Sub-kingdom—Annulosa[48].

Class—Insecta.

First Definition—From their external Organization.

• Body—divided into Head—Trunk—Abdomen.
  • Head.—Principal seat of the organs of sensation.
    
    • Organs of sight. Immoveable eyes, simple or compound, varying in number.
    • Organs of hearing uncertain, probably connected with the antennæ.
    • Organ of taste. Ligula or palate within the mouth, accompanied by the organs of manducation—a pair of mandibles and maxillæ and an upper and lower lip, or their representatives.
    • Organs of touch. Principally two jointed antennæ or their representatives, and four jointed feelers—two maxillary and two labial.
  • Trunk. Principal seat of the organs of motion.
    
    • Organs of walking, running, or jumping. Six or eight jointed thoracic legs, in pairs.
    • Organs of flight. Four wings or their representatives,[Pg 29] mostly with branching nervures containing air-vessels; found in the majority of the class.
    • Organs (external) of respiration. A double set of lateral spiracles, some for expiration.
  • Abdomen. Principal seat of the organs of generation.
    
    • Organs of motion. In the Myriapods many pairs of acquired legs; in the Thysanura elastic ventral or caudal appendages.
    • Organs of respiration. A double series of lateral spiracles for inspiration in the majority; in some only a single series, and in others only a single pair.
    • Organs of generation those common to the Vertebrata, but retractile within the body, attended usually by various anal appendages, particularly a forceps in the males, and an ovipositor in the females.

Second Definition—From their internal Organization.

• Sensation.
  • Nervous System. A small brain usually subbilobed, crowning a knotty double medullary chord; nerves proceeding from the brain and other ganglions to all parts of the body.
• Circulation.
  • Heart replaced by a simple alternately contracting dorsal vessel or pseudocardia, without arteries or veins, but filled with a white cold sanies.
• Respiration.
  • Lungs replaced by tracheæ, which receive the air from the spiracles, and distribute it by bronchiæ infinitely ramified.
• Digestion.[Pg 30]
  • Liver and biliary vessels in most replaced by from 2 to + 150 floating hepatic filaments opening into the space between the two skins of the intestinal canal below the pylorus.
• Generation.
  • Internal organs. Males—Vasa deferentia, and vesiculæ seminales, and the other ordinary organs. Females—Ovary usually bipartite, with palmate lobes; genital organs single and mostly anal; one sexual union impregnates the female for her life.
  • Development. In their passage to their adult state, after they have left the egg, insects undergo several simultaneous changes of their integument or successive moults, and the majority assume three distinct forms, with distinct organs, which appear as rudiments in their second state, and are completely developed in their last.

In defining the Arachnida I shall only mention those particulars in which they differ from Insectæ in their external anatomy.

Class—Arachnida.

• Body.
  • Head and Trunk usually not separated by a suture.
    
    • Eyes. Two to eight, not lateral.
    • Mandibles cheliform or unguiculate, representing the interior pair of the antennæ of the Crustacea.
    • Palpi pediform or cheliform.
    • Trunk. Legs eight or their representatives: tibiæ mostly consisting of two joints.
  • Abdomen with from two to eight spiracles.
    
• Sensation.[Pg 31]
  • Nervous System. A small bilobed brain crowning a double, knotty, medullary chord; nerves proceeding from the brain and other ganglions to all parts of the body.
• Circulation.
  • Heart unilocular, inaurite, with a system of circulation by arteries and veins; blood a cold white sanies.
• Respiration.
  • Lungs replaced by internal gills receiving the air by spiracles.
• Digestion.
  • Liver, consisting of conglomerate glands, and enveloping the intestines[49]; hepatic ducts.
• Generation.
  • Genital organs double, ventral; more than one sexual union in the course of life.

The external characters in this class are the same almost in every respect as those which distinguish the Phalangidæ, the whole difference consisting almost in the systems of circulation, respiration, and digestion. Perhaps some future anatomist may discover in the tribe just mentioned, that there is a nearer agreement between them and the Arachnida in these systems than is at present suspected, which would prove them true Arachnida. I am inclined to think that Phrynus and Gonyleptes, &c. breathe by branchial spiracles; but having no opportunity[Pg 32] of examining living specimens, I dare not speak with any confidence on the subject.

Having thus given you a view of the most important diagnostics by which what we have all along called Insects may scientifically be distinguished from other invertebrate animals, it may not be without use, if, under this head, I take a more popular and familiar view of the subject, and say something upon those distinctions which may attract the attention of the more common observer.

The notion of diminutive size, particularly as compared with vertebrate animals, seems more frequently attached to the idea of an insect than any other; and this notion is generally correct, for one insect that is bigger than the least of the above animals, thousands and thousands are vastly smaller: but there exist some that are considerably larger, whether we take length or bulk into consideration, and this in almost every order. To prove this most effectually, and that you may have a synoptical view of the comparative size of the larger insects of the different orders and tribes, I now lay before you a table of the dimensions of such of the largest as I have had an opportunity of measuring, including particularly those giants that are natives of the British isles.[Pg 33]

[Pg 38]

From this table you see that several insects included in it exceed some of the smallest Vertebrata in bulk. In the Mammalia, the Sorex Araneus, called by the common people here the Ranny, is not more than two inches long excluding the tail; and the Mus messorius, or harvest-mouse, peculiar to the southern counties of England, is still more diminutive: so that to these little animals, the larger Dynastidæ, Goliathi, and Prioni, &c., appear giants, and may compete with the mole in size. Even some of the beetles of our own country, as the great Hydrophilus, the stag-beetle, &c., are more bulky than the two first-named quadrupeds. Amongst the birds, many Picæ, Passeres, &c., yield to several insects in dimensions, and their wings when expanded do not extend so far as those of not a few Lepidoptera. The great owl-moth of Brazil (Erebus Strix) in this respect is a larger fowl than the quail. Those beautiful little creatures, the humming-birds (Trochilus L.), the peculiar ornament and life of tropical gardens, which emulate the most splendid butterflies in the brilliancy of their plumage, are smaller than a considerable number of insects in almost every order, and even than some of those that are natives of Britain. Various reptiles also are much inferior in size to many of the insects of the above table. The smallest lizard of this country would be outweighed by the great British beetles lately mentioned, and the mole-cricket (Gryllotalpa vulgaris); and some of the serpent tribe are smaller than the larger Scolopendræ and Iuli. Amongst the fishes also, though some are so enormous in bulk, others in this respect yield the palm to several insects. The minnow and the stickleback that frequent our own pools and streams are considerably inferior in size to some of our water beetles.

[Pg 39]

In looking over the table, and comparing the different species that compose it with each other, you will perceive that the largest insects of the two sections of Hemiptera, of the Lepidoptera as to their body merely, of the Hymenoptera and Diptera, in general size fall considerably short of those of the other orders; and that certain individuals of the Orthoptera and Aptera bear away the palm in this respect from all the rest. In the Coleoptera the giants, with the exception of the Goliathi, are chiefly to be found amongst the timber devourers in the Lamellicorn and Capricorn tribes. Of orthopterous insects the Phasmidæ present the most striking examples of magnitude; and in the Neuroptera, the Agrionidæ of great length.

It is worthy of remark here, that although the tropical species of a genus usually exceed those of colder climates in size, the Gryllotalpa of Brazil is very considerably smaller than that of Europe: whether this is the case with the rest of the cricket tribe I have not had an opportunity of ascertaining. The Lepidoptera, though often remarkable for the vast expansion of their "sail-broad vans," if you consider only their bodies, never attain to gigantic bulk. Even the hawk-moths (Sphinx L.), though usually very robust, make no approach to the size of the great beetles, or the length of some of the spectres (Phasma) and dragon-flies (Agrionidæ). With regard to the superficial contents of their wings, a considerable difference obtains in different species where they expand to the same length—for the secondary wings are sometimes smaller than the primary, and sometimes they equal them in size. In some instances, also, the latter although long are narrow, and in others they are nearly as wide as long: regard, therefore, should be had to their expansion[Pg 40] both ways. In the Hymenoptera and Diptera, the principal giants are to be found in the predaceous or blood-sucking tribes, as Scolia, the Sphecidæ, Pompilidæ, Vespidæ, &c., belonging to the former order; and the Asilidæ and Tabanidæ to the latter. The true and false humble bees (Bombus and Xylocopa) and the fly tribe (Muscidæ), though they sometimes attain to considerable size, scarcely afford an exception to this observation. Amongst the Aptera none of the Hexapods strike us by their magnitude, and few of the Octopods, though the legs of some of the Phalangidæ inclose a vast area. That in the table would with them describe a circle of six inches diameter, though its body is little more than a quarter of an inch in length. The Myriapods exceed most insects in the vast elongation of their body, which with their motion gives them no slight resemblance to the serpents. In the class Arachnida, the bird-spiders (Mygale) are amongst the principal giants, nor do the Scorpions fall far short of them—both of them when alive often alarming the beholder as much by their size as by their aspect.

But as I have before observed, generally speaking, one of the most remarkable characters of the insect world, is the little space they occupy; for though they touch the vertebrate animals and even quadrupeds by their giants, yet more commonly in this feature they go the contrary way, and by their smallest species reach the confines of those microscopic tribes that are at the bottom of the scale of animal life. I possess an undescribed beetle, allied to Silpha minutissima E. B.[50] which, though furnished[Pg 41] with elytra, wings, antennæ, legs, and every other organ usually found in the order it belongs to, is absolutely not bigger than the full stop that closes this period. In several other coleopterous genera there are also very minute species, as in Cryptophagus, Anisotoma, Agathidium, &c. I know no orthopterous insect that can be called extremely minute, except that remarkable one found on the Continent in the nests of ants, the Blatta Acervorum of Panzer[51], but now called, I believe, Myrmecophilus: nor indeed any in the Hemiptera, Neuroptera, and Diptera, that approach the extreme limits of visibility: but in the Lepidoptera, the pygmy Tinea occultella is almost invisible except in flight, being scarcely thicker than a horse's hair, and proportionably short; indeed, many others of those lovely Lilliputians, the subcutaneous Tineæ, decorated with bands of gold and silver, and studded with gems and pearls, that in larger species would dazzle the beholder's eye, are in size not much more conspicuous. In the Hymenoptera order, Ichneumon Punctum of Dr. Shaw, which forms so striking a contrast to his giant Phasma dilatatum, being placed together in the same plate; and another that I possess, under the trivial name of Atomos, would elude the searching eye of the entomologist unless when moving upon glass. Linné named the tribe of parasites to which these belong, Minuti, on account of their generally diminutive size. But these little minims, under the superintendence of Providence, are amongst the greatest benefactors of the[Pg 42] human race, since they keep within due bounds the various destroyers of our produce.

The number of minute species of insects seems greatly to exceed that of large ones, at least in Europe, of which it may be asserted probably with truth, that two-thirds are under a quarter of an inch in length, and one-third not exceeding much a duodecimal of it. It might hold good perhaps in Coleoptera, Hymenoptera, Diptera, and Aptera: but in Orthoptera, Hemiptera, Neuroptera, and especially Lepidoptera, a large proportion would be found to exceed three lines in length. Neither can it be affirmed of extra-European species, of those at least preserved in cabinets, amongst which it is rare to find an insect less than the fourth of an inch long. This, however, must probably be attributed to the inattention of collectors, who neglect the more minute species.

Though size forms a pretty accurate distinction between insects and the great bulk of vertebrate animals, it affords less assistance in separating them from the invertebrate classes, which are of every size, from the monstrous bulk of some Cephalopoda (cuttle-fish) and Mollusca (shell-fish, &c.) to the invisible infusory animalcule: but external characters, abundantly sufficient for this purpose, may be drawn from the general covering, substance, form, parts, and organs of the body. As I shall enter into pretty full details upon this subject when I come to treat of the external anatomy of insects, I shall here, therefore, only give such a slight and general sketch of the distinctions just mentioned, as will answer the end I have in view. I must here repeat what I have before observed, and what it is necessary that you should always bear in mind, namely,[Pg 43] that at the limits of classes and of every other natural group, the characters begin to change, those peculiar to the one group beginning gradually to disappear, and those of the other to show themselves; so that it is impossible almost to draw up a set of characters so precise as exactly in every respect to suit all the members of any natural group.

Whichever way we turn our eyes on the objects of creation, above—below—athwart, analogies meet us in every direction, and it appears clear, that the Book of Nature is a Book of Symbols, in which one thing represents another in endless alternation. And not only does one animal, &c. symbolize another, but even between the parts and organs of one set of animals there is often an analogy as to their situation and use, when there is little or no affinity as to their structure—or again, the analogy is in their situation, without affinity in either structure or use. Thus certain parts in one tribe represent other certain parts of another tribe, though as to their structure there is often a striking disagreement. This is particularly observable between the vertebrate and invertebrate animals. I shall therefore, in my remarks on the general and particular structure of insects, contrast it in its most important points with that of the first-mentioned tribe.

The first thing that strikes us when we look at an insect is its outside covering, or the case that incloses its muscles and internal organs. If we examine it attentively, we find that it is not like the skin of quadrupeds and other Vertebrata, covering the whole external surface of the body; but that in the large majority it consists of several pieces or joints, in this respect resembling the[Pg 44] skeleton of the animals just named; and that even in those in which the body appears to have no such segments, as in many of the Mites (Acarus L.), they are to be found in the limbs. This last circumstance, to have externally jointed legs, is the peculiar and most general distinction by which the Insecta of Linné, including the Crustacea, may always be known from the other invertebrate animals[52].

If we proceed further to examine the substance of this crust or covering, though varying in hardness, we shall find it in most cases, if we exclude from our consideration the shells of the Mollusca, &c., better calculated to resist pressure than that of the majority of animals that have no spine. In all the invertebrate tribes, indeed, the muscles, there being no internal skeleton, are attached to this skin or its processes, which of course is firmer than the internal substance; but in insects it is very often rigid and horny, and partially difficult to perforate, seldom exhibiting that softness and flexibility which is found in the cuticle of birds and most quadrupeds. From this conformation it has been sometimes said, that insects carry their bones on the outside of their body, or have an external skeleton. This idea, though not correct in all respects, is strictly so in this—that it affords a general point of support to the muscles, and the whole structure is erected upon it, or rather I should say within it. The difference here between Insects and the Vertebrata seems very wide; but some of the latter make an approach towards it. I allude to the Chelonian Reptiles (Testudo L.),[Pg 45] in which the vertebral column becomes external or merges in the upper shell. The cyclostomous fishes also are not very wide of insects as to their integument. But on this subject I shall be more full hereafter.

The forms of insects are so infinitely diversified that they almost distance our powers of conception: in this respect they seem to exceed the fishes and other inhabitants of the ocean, so that endless diversity may be regarded as one of their distinctions. But on all their variations of form the Creator has set his seal of symmetry; so that, if we meet with an animal in the lower orders in which the parts are not symmetrical, we may conclude in general that it is no insect.

But it is by their parts and organs that insects may be most readily distinguished. In the vertebrate animals, the body is usually considered as divided into head, trunk, and limbs, the abdomen forming no part of the skeleton; but in the insect tribes, besides the organs of sense and motion, the body consists of three principal parts—Head, Trunk, and Abdomen—the first, as was before observed, bearing the principal organs of sense and manducation; the second most commonly those of motion; and the third those of generation—the organs of respiration being usually common to both trunk and abdomen. These three primary parts,—though in some insects the head is not separated from the trunk by any suture, as for instance in the Arachnida; and in others, head, trunk, and abdomen form only one piece, as in some mites,—still exist in all, and in the great majority they are separated by incisures more or less deeply marked: this is particularly visible in the Hymenoptera and Diptera, which, in this respect, are formed upon a common model;[Pg 46] and in the rest, with the above exceptions, it may be distinctly traced.

The head of insects is clearly analogous to that of vertebrate animals, except in one respect, that they do not breathe by it. It is the seat probably of the same senses as seeing, hearing, smelling, tasting—and more peculiarly perhaps of that of touch. The eyes of insects, though allowed on all hands to be organs of sight, are differently circumstanced in many particulars from those of the animals last mentioned; they are fixed, have neither iris nor pupil, are often compound, and are without eyelids to cover them during sleep or repose; there are usually two compound ones composed of hexagonal facets, but in some instances there are four; and from one to three simple in particular orders. The antennæ of insects in some respects correspond with the ears of the animals we are comparing with them; but whether they convey the vibrations of sound has not been ascertained: that they receive pulses of some kind from the atmosphere I shall prove to you hereafter—so that if insects do not hear with them in one sense, they may, by communicating information, and by aëroscopy, to use Lehman's term, not directly in his sense[53], supply the place of ears, which would render them properly analogous to those organs. That in numbers these remarkable organs are tactors is generally agreed, but this is not their universal use. That insects smell has been often proved; but the organ of this sense has not been ascertained. What has improperly been called the clypeus, or the part terminating the face above the upper lip (labrum), is in the situation of the nose of the Vertebrata,[Pg 47] and therefore so far analogous to it, and in some cases even in form: I therefore call it the nose. Whether this part represents the nose by being furnished with what answer the purpose of nostrils, residing somewhere at or above the suture that joins it to the upper lip, I cannot positively affirm; but from the observations of M. P. Huber, with regard to the hive-bee, it appears that at least these insects have the organ of the sense in question somewhere in the vicinity of the mouth, and above the tongue[54]: analogy, therefore, would lead us to look for its site somewhere between the apex of the nose and the upper lip; and in some other cases, which I shall hereafter advert to, there is further reason for thinking that it actually resides at the apex of the nose. The organ of taste in insects, though some have advanced their palpi to that honour, is doubtless in some part within the mouth analogous in a degree to the tongue and palate of the higher animals. The organs of manducation, in what may be deemed the most perfect description of mouth, consist of an upper lip closing the mouth above, a pair of mandibles moving horizontally that close its upper sides, and a lower lip with a pair of maxillæ attached to it, which close the mouth below and on the under sides, both labium and maxillæ being furnished with jointed moveable organs peculiar to annulose pedate animals, called palpi. In some tribes these organs assume a different form, that they may serve for suction; but though in many cases some receive an increment at[Pg 48] the expense of others, and a variation in form takes place, none, as M. Savigny has elaborately proved, are totally obliterated or without some representative[55]. The organs now described, except the upper lip, are formed after a quite different type from those of Vertebrata, with which they agree only in their oral situation and use.

The second portion of the body is the Trunk, which is interposed between the head and abdomen, and in most insects consists of three principal segments, subdivided into several pieces, which I shall afterwards explain to you. I shall only observe, that some slight analogy may perhaps be traced between these pieces and the vertebræ and ribs of vertebrate animals, particularly the Chelonian reptiles. This is most observable in Gryllus L. and Libellula L., in which the lateral pieces of the trunk are parallel to each other[56]. In the Diptera and many of the Aptera most of these pieces are not separated by sutures. Each of the segments into which the trunk is resolvable bears a pair of jointed legs, the first pair pointing to the head, and the two last to the anus. These legs in their composition bear a considerable analogy to those of quadrupeds, &c., consisting of hip, thigh, leg, and foot; but the last of these, the foot or Tarsus, is almost universally monodactyle, unless we regard the Calcaria that arm the end of the tibia, as representing fingers or toes, an idea which their use seems to justify. Acheta monstrosa and Tridactylus paradoxus, however[57], exhibit some appearance of a phalanx of these organs. They differ from them first in number, the thoracic legs being[Pg 49] invariably six in all insects, with the exception of the Octopods or most of the Trachean Arachnida, which have usually eight. In the Myriapods, though there are hundreds of abdominal legs, only six are affixed to the trunk. Next they differ with regard to the situation of their legs; for though the anterior pair or arms are analogous in that respect, the posterior pair are not, since in quadrupeds these legs are placed behind the abdomen, but in insects before it—in fact, in the former the legs may be considered as placed at each end of the body, excluding only the head and tail, but in the latter in the middle. Though they correspond with those of quadrupeds in being in pairs or opposite to each other, yet their direction with respect to the body is different, the legs of quadrupeds, &c. being nearly straight, whereas in insects they are bent or form an angle, often very obtuse at the principal articulations, which occasions them to extend far beyond the body, and when long to inclose a proportionally greater space. The wings are the organs of motion with which the upper side of the trunk is furnished; and these, though they are the instruments of flight, are in no other respect analogous to those of birds, which replace the anterior legs of quadrupeds, but approach nearer, both in substance and situation, to the fins of some fishes, and perhaps in some respects even to the leaves of plants. M. Latreille is of opinion, That the four wings or their representatives replace the four thoracic legs of the decapod Crustacea[58]. Upon this opinion, which shows great depth of research and practical acumen, I shall have occasion to express my sentiments when I come to treat more at large on the anatomy[Pg 50] of the trunk and its members; at any rate they do not replace the two anterior pair of legs of the hexapod Aptera. When merely used as wings, they commonly consist of a fine transparent double membrane, strengthened by various longitudinal and transverse nervures, or bones as some regard them, accompanied by air-vessels, of which more hereafter, as well as of their kind and characters. I shall only observe, that insects are known from all other winged animals, by having four wings, or what represent them, and this even generally in those that are supposed to have only a pair. Another peculiarity distinguishes the trunk of insects that you will in vain look for in the vertebrate animals—these are one or two pair of lateral spiracles or breathing pores. Though the respiratory sacs, &c. of birds are almost as widely dispersed as the tracheæ and bronchiæ of insects[59], yet their respiration is perfectly pulmonary, and nothing like these pores is to be discovered in them.

The principal peculiarity of the third part of the body, the abdomen, is its situation behind the posterior pair of thoracic legs, and its rank as forming a distinct portion of what represents the skeleton. In most insects it is so closely affixed to the posterior part of the trunk as to appear like a continuation of it, but in the majority of the Hymenoptera and Diptera, and in the Araneidan Arachnida, or spiders, it is separated by a deep incisure; and in the first-mentioned tribe is mostly suspended to the trunk by a footstalk, sometimes of wonderful length and tenuity. In the Mammalia the male genital organs are partly external; but in insects as well as in many of the vertebrate animals, except when employed, they are[Pg 51] retracted within the body. This part is the principal seat of the respiratory pores or spiracles, many having eight in each side, while others have only one.

Such are the principal external characters which distinguish Insecta and Arachnida, or what we have heretofore regarded as insects, to which here may be added another connected with their internal organization. The union of the sexes takes place in the same manner as amongst larger animals; and the females with very few exceptions, more apparent than real, are oviparous. They are, however, distinguished by this remarkable peculiarity already alluded to, that, except in the case of the Arachnida, one impregnation fertilizes all the eggs they are destined to produce. In most cases, after these are laid, the females die immediately, and the males after they have performed their office, though they will sometimes unite themselves to more than one female. One other circumstance may be named here—that no genuine insect or Arachnidan has yet been found to inhabit the ocean.

Before I conclude this letter, it is necessary to apprize you, that every thing which it contains relative to the characters of insects, has reference to them only in their last or perfect state, not in those preparatory ones through which you are aware that the majority of them must pass. The peculiar characteristics of them in these states—in the egg, the larva, and the pupa, will be the subjects of my next letters, which will be devoted to a more detailed view of the metamorphosis of insects than I gave you before when adverting to this subject[60].

[Pg 52]

LETTER XXIX.

STATES OF INSECTS.

EGG STATE.

On a former occasion I gave you a general idea of what has been called, perhaps not improperly, the metamorphosis of insects[61]; but since that time much novel and interesting speculation on the subject has employed the pens of many eminent Physiologists; and besides this, the doctrine then advanced of successive developments has been altogether denied by a very able Anatomist, Dr. Herold, who, with a hand, eye, and pencil, second only to those of Lyonnet, has traced the changes that gradually take place in the structure of the cabbage-butterfly (Pieris Brassicæ) on passing through its several states of larva, pupa, and imago. It is necessary, therefore, that previously to considering separately and in[Pg 53] detail the states of insects, I should again call your attention to this subject, and endeavour to ascertain whether Dr. Herold's hypothesis rests upon a solid foundation; or whether that adopted from Swammerdam by all the most eminent Entomologists and Physiologists since his time can be maintained against it.

I shall first give you a short abstract of the new hypothesis.

According to Dr. Herold—The successive skins of the caterpillar, the pupa-case, the future butterfly, and its parts and organs, except those of sex which he discovered in the newly excluded larva, do not preexist as germes, but are formed successively from the rete mucosum, which itself is formed anew upon every change of skin from what he denominates the blood, or the chyle after it has passed through the pores of the intestinal canal into the general cavity of the body, where, being oxygenated by the air-vessels, it performs the nutritive functions of blood. He attributes these formations to a vis formatrix (Bildende Kraft).

The caul or epiploon (Fett-masse), the corps graisseux of Reaumur, &c., which he supposes to be formed from the superfluous blood, he allows, with most physiologists, to be stored up in the larva, that in the pupa state it may serve for the development of the imago. But he differs from them in asserting that in this state it is destined to two distinct purposes—first, for the production of the muscles of the butterfly, which he affirms are generated from it in the shape of slender bundles of fibres;—and secondly, for the development and nutrition of the organs formed in the larva, to effect which, he says, it is dissolved again into the mass of blood, and being oxygenated by the air-vessels,[Pg 54] becomes fit for nutrition, whence the epiploon appears to be a kind of concrete chyle[62].

Need I repeat to you the hypothesis to which this stands opposed—That every caterpillar at its first exclusion contains within itself the germe of the future butterfly and of all its envelopes, which successively presenting themselves are thrown off, till it appear in perfection and beauty, with all its parts and organs, when no further development takes place.

I believe you will agree with me, when you have read and considered the above abstract of Dr. Herold's hypothesis, that in it he substitutes a name for knowledge, talks of a vis formatrix because his assisted eye cannot penetrate to the primordial essence or state of the germes of being, and denies the existence of what he cannot discover[63]. From ancient ages philosophers have done the same, to conceal their own ignorance of causes under a sounding name, when they have endeavoured to penetrate within the veil of the sanctum sanctorum, which it is not permitted to vain man to enter. This has occasioned the invention, not only of the term in question, but of many others, as little meriting the appellation of Signs of ideas; such as Plastic Nature, Epigenesis, Panspermia, Idea seminalis, Nisus formativus, &c. But upon[Pg 55] this subject you cannot do better than consult what the learned Dr. Barclay has said in his admirable work On Life and Organization[64], in which he has placed the inanity, the vox et præterea nihil, of such high-sounding terms in their true light. The processes of nature in the formation and development of the fœtus in utero, of the chick in the egg, of the butterfly in the caterpillar, we in vain attempt fully to investigate; yet we can easily comprehend that pre-existent germes, by the constant accretion of new matter in a proper state, may be gradually developed, but we find it impossible to conceive how, by the action of second causes, without the intervention of the first cause, the butterfly should be formed in the caterpillar, unless it preexists there as a germe or fœtus. "Is it not clear," asks Dr. Virey in his lively manner, "as Blumenbach and other Physiologists maintain, that there is a formative power, a nisus formativus, which organizes the embryo? Admirable discovery!" says he, "which teaches us that the fœtus forms itself because it forms itself! As if you should affirm that the stone falls because it falls[65]!" Had Dr. Herold considered what Bonnet says with as much good sense as modesty, he would never have imagined that his discovering the organs of the butterfly one after the other at certain periods in the caterpillar, was any sound argument against their preexistence and coexistence as germes. "Organs," says that amiable and excellent Physiologist, "that have no existence as to us, exist as they respect the embryo, and perform their essential functions; the term of their becoming visible is that which has been[Pg 56] erroneously mistaken for the period of their existence[66]." This has been Dr. Herold's grand error; he mistook the commencement of the appearance of the organs of the butterfly for that of their existence, and yet the early appearance of the sexual organs ought to have led him to a conclusion the reverse of that which he has adopted.

Dr. Virey has observed with great truth—that "Every being has a peculiar and unique nature, which would be impossible if the body was composed of parts made at several intervals, and without a uniform power that acts by concert[67]:" and every Physiologist acquainted with the history of insects that undergo a complete metamorphosis will allow, that their developments and acquisition of new parts and organs take place according to a law which regulates the number, kind, and times of them, differing in different species, and which has had an invariable operation, since the first creation, upon every sound individual that has been produced into the world.

In consequence of this law, one species changes its skin only four times, and another five or six;—in some cases the first skins shall be covered or bristled with hairs or spines, and the last be naked and without arms;—that which forms the case of the pupæ shall differ in form and substance from the preceding skins, varying in both respects in different species; and finally the butterfly shall invariably follow, when no other change but the[Pg 57] last mortal one shall take place. Can this law, so constantly observed, be the result of a blind power? Or are we to suppose that the Deity himself is always at work to create the necessary organs in their time and place? Is it not much more consonant to reason and the general analogy of nature, to suppose that these parts and organs exist in embryo in the newly-hatched caterpillar, and grow and are successively developed by the action of the nutritive fluid? In the pupa of many Diptera the inclosed animal, even under the microscope, appears without parts or organs, like a mere pulp; but Bonnet tells us, that if boiled, all the parts of the pupa appear[68], which proves the preexistence of these parts even when not to be discerned, and that nothing but the evaporation of the fluids in which they swim is wanted to render them visible.

Mr. William MacLeay has with great truth observed: "The true criterion of animal as well as vegetable perfection is the ability to continue the species[69];" and in their progress to this state certain changes take place in the parts and organs of all animals and vegetables: there is, therefore, an analogy in this respect between them; and this analogy also furnishes another argument against Dr. Herold's hypothesis, as we shall presently see. These changes are of three kinds: In the vegetable kingdom, at least in the phænogamous classes, there is a succession of developments terminating in the appearance of the generative organs, inclosed in the flower; in this kind the integuments, or most of them, are usually persistent. In insects and other annulose and some vertebrate animals, there is a succession of spoliations, or[Pg 58] simultaneous changes of the whole integument, till the animal appears in its perfect form with powers of reproduction; in this kind the integuments are caducous.—In man and most of the vertebrate animals there is a gradual action of the vital forces in different organs till they are fitted for reproduction; accompanied, as progress is made to the adult state, by the acquisition of certain organs, &c. as of teeth, horns, pubes, feathers, &c.[70] Let us now consider a little in detail the analogies that appear to exist between the second and the first and third kinds. I shall first consider the latter as the least obvious. That able, judicious, and learned physiologist, Dr. Virey, has pointed out no inconsiderable resemblance between the metamorphosis of the insect, and the changes, which he denominates a metamorphosis by metastasis, to which most vertebrate animals are subject. In them, he observes, a state analogous to the larva state begins at the exclusion of the fœtus from the womb; it is deprived of teeth, and its viscera are only accommodated to milk: in the cornute species the horns are in embryo: the digestive system now preponderates, and the great enjoyment is eating. A second state, in a degree analogous to that of pupa, commences at the period of dentition—the teeth now produce another modification in the intestinal canal, which becomes capable of receiving and digesting solid food: during this period the vital forces are all tending to produce the perfect state of the animal; and in this state, in man especially, the individual is educated and fitted to discharge the duties of active life. Again, analogous to the imago state is the age of puberty, in which[Pg 59] the complete development of the sexual powers takes place in both sexes, and the animal has arrived at its acme, and can continue its kind[71]: now the digestive powers diminish in their activity, and love reigns paramount. When this state is fully attained, no further or higher change is to be expected, and the progress is soon towards decay and the termination of the animal's mortal career. So we see that in fact man and other mammalia, though they do not simultaneously cast their skins like the insect; or pass into a state of intermediate repose, before they attain the perfection of their nature, like the caterpillar; have their three states, in each of which they acquire new parts, powers, and appetites.

But a more striking analogy has been traced between the insects that undergo a complete metamorphosis and the vegetable kingdom; for though the primary analogy seems to be between the Polypus and the Plant, yet the secondary one with the Insect is not by any means remote. There are circumstances to which I shall have occasion hereafter to call your attention, which afford some ground for supposing, that the substance of the insect and the vegetable partakes of the same nature, at least approximates more nearly, than that of the insect and the vertebrate animal; and every one who has observed these little creatures with any attention, will have observed amongst them forms and organs borrowed as it were from the kingdom of Flora; and vice versâ the Botanist, if he makes the comparison, will find amongst his favourite tribes many striking resemblances of certain insects. But the analogy does not stop here; for the butterfly and the plant appear to have been created with a particular[Pg 60] reference to each other, both in the epoch of their appearance and the changes that take place in them. Thus, as Dr. Virey has observed, the caterpillar is simultaneous with the leaf of the tree or plant on which it feeds, and the butterfly with the flowers of which it imbibes the nectar[72]. Swammerdam, I believe, was the first who noticed the analogy between the changes of the insect and the vegetable, and has given a table in which he has contrasted their developments, including other animals that undergo a metamorphosis[73]: an idea which has been generalized by Bonnet[74], and adopted and enlarged by Dr. Virey[74]. A state analogous to that of the larva in the insect begins in the plant when it is disclosed from the seed, or springs from its hybernaculum in the bulb, &c., or is evolved from the gemma; integument after integument, often in various forms, as cotyledon, radical, cauline, or floral leaves, expands as the stem rises, all which envelopes incase the true representative of the plant, the fructification, as the various skins do the future butterfly. When these integuments are all expanded, the fructification appears inclosed by the calyx or corolla as the case may be, in which the generative organs are matured for their office—this is the bud, which is clearly analogous to the pupa state of the insect. Next the calyx and corolla expand, the impregnation of the germen takes place, and the seed being ripened, and dispersed by the opening of the seed-vessel or ovary of the plant, the individual dies: thus the imago state of the insect has its representative in the plant. "If we place," says Dr. Virey, "here the egg of the insect, next its caterpillar, a little[Pg 61] further the chrysalis, and lastly the butterfly—what is this but an animal stem—an elongation perfectly similar to that of the plant issuing from the seed to attain its blossoming and propagation?"[75]

There being, therefore, this general analogy in their progress to that state in which they can continue their species between every part of animated nature, it holds good, I think, that the same analogy should take place in their developments. If the adult man or quadruped, &c. is evidently an evolution of the fœtus, as from microscopical observations it appears that they are[76], if the teeth, horns, and other parts, &c. to be acquired in his progress to that state are already in him in their embryos, we may also conclude that the butterfly and its organs, &c. are all in the newly-hatched caterpillar. Again, if the blossom and its envelopes are contained in the gemma, the bulb, &c. where they have been discovered[77], it follows analogically that the butterfly and its integuments all preexist in its forerunner.

Perhaps after this view of the objections to Dr. Herold's hypothesis, it will not be necessary to say much with regard to the argument he draws from the change of organs—the loss of some and the acquisition of others—since this may readily be conceived to be the natural consequence of the vital forces tending more and more to the formation of the butterfly, and the withdrawing of their action more and more from the caterpillar; I shall not, therefore, enter further into the question, especially[Pg 62] since the change of organs will come more regularly under our notice upon a future occasion.

Winged insects, many branchiopod Crustacea, and the Batracian reptiles, have been observed by Dr. Virey to bear some analogy to the mammalia, aves, &c. in another respect. In leaving their egg, they only quit their first integument, answering to the chorion or external envelope of the human fœtus; they therefore still continue a kind of fœtus, so to speak, more or less enveloped under other tunics, and principally in their amnios, or the covering in which the fœtus floats in the liquor amnii[78]. This the butterfly does in the pupa case; and its birth from this, under this view, will be the true birth of the animal. In the human subject, the ova upon impregnation are said to pass from the ovary through the Fallopian tube into the uterus. In the insect world, upon impregnation, the eggs pass first from the ovaries into the oviduct, answering to the Fallopian tube, which in them terminates in the ovipositor, or the instrument by which the parent animal conveys the eggs to their proper station: there is, therefore, nothing properly analogous to the uterus in the insect, and the substance upon which the larva feeds upon exclusion answers the purpose of a placenta.

After this general view of the most modern theories with regard to the metamorphosis of insects, I shall in the present and some following letters, treat separately of the different states through which these little beings successively pass.

The first of these is the Egg state, the whole class of insects being strictly oviparous. Some few tribes indeed[Pg 63] bring into the world living young ones, and have on that account been considered as viviparous, but incorrectly, for the embryos of none of these are nourished, as in the true viviparous animals, within a uterus by means of a placenta, but receive their development within true eggs which are hatched in the body of the mother. This is proved by the observations of Leeuwenhoek, who found eggs in the abdomen of a female scorpion[79]; and of Reaumur, with regard to the flesh-fly (Musca carnaria) and other viviparous flies as they have been called[80]. A similar mode of production takes place in vipers and some other reptiles, which have hence been denominated ovo-viviparous, to distinguish them from the true viviparous animals—the class Mammalia. By far the larger portion of insects is oviparous in the ordinary acceptation of the term. The ovo-viviparous tribes at present known are scorpions; the flesh-fly and several other flies; a minute gnat belonging to Latreille's family of Tipulariæ[81]; some species of Coccus; some bugs (Cimicidæ)[82]; and most Aphides, which last also exhibit the singular fact of individuals of the same species being some oviparous and others ovo-viviparous, the former being longer in proportion than the latter.—Bonnet, however, is of opinion that the eggs of the first are not perfect eggs, but a kind of cocoon, which defends the larva, already formed in some degree, from the cold of winter[83].

[Pg 64]

When excluded from the body of the mother, or from the egg, as has been before observed, some insects appear nearly in the form of their parents, which, with a very slight alteration, they always retain; others, and the greater number, assume an appearance totally different from that of their parents, which they acquire only after passing through various changes. It is to these last, which have chiefly engaged the attention of Entomologists, that the title of metamorphoses has been often restricted. As, however, those insects which undergo the slightest change of form, as spiders do, undergo some change, and almost all insects cast their skins several times[84] before they attain maturity, Linné and most Entomologists, till very recently, have regarded the whole class as undergoing metamorphoses, and as passing through four different states, viz. the Egg—the Larva—the Pupa—and the Imago.

It is obvious, however, that in ovo-viviparous species three states of their existence only come under our cognizance, as these, being hatched in the body of the mother, come forth first under the form of larvæ. There is even one tribe of insects which presents the strange anomaly of being born in the pupa state. This is the Linnean genus Hippobosca (Pupipara fam. Latr.), to which our forest-fly belongs, the females of which lay bodies so much resembling eggs, that they were long considered as such until their true nature was ascertained by Reaumur (most of whose observations were confirmed by De Geer), who, from their size, which nearly equals[Pg 65] that of the parent fly—from their slight motion when first extruded—from spiraculiform points which run down each side of them—and lastly, from their producing not a larva, as all other insects' eggs do, but perfect flies in the winged state—inferred, and doubtless with reason, that they are not real eggs, but pupæ, or larvæ just ready to assume the pupa state, which, however strange it may seem, have passed the egg and larva states in the body of the mother[85].

Insects, therefore, as to their mode of birth, may be divided into—

I. Ovo-viviparous, subdivided into—

1. Larviparous, coming forth from the matrix of the mother in the state of larvæ, as the Scorpion (Scorpio), the Flesh-fly (Musca), the Plant-louse (Aphis), &c.

2. Pupiparous, continuing in the matrix of the mother during the larva state, and coming forth in that of pupa, as the Forest-fly (Hippobosca equina), the Sheep-louse (Melophagus ovinus), the Bat-louse (Nycteribia Vespertilionis), &c.

II. Oviparous. All other insects.

Our business for the remainder of this letter will be with the latter description of these little animals.

The unerring foresight with which the female deposits her eggs in the precise place where the larvæ, when excluded, are sure to find suitable food; and the singular instruments with which, for this purpose, the extremity of their abdomen is furnished, have been noticed in a former letter[86], and those last mentioned will be adverted to in a future one. I shall now, therefore, confine myself[Pg 66] to other circumstances connected with the subject, arranged for the sake of order under several distinct heads, as—their exclusion—situation—substance—number—size—figure—colour—and period of hatching.

i. Exclusion. The exclusion or extrusion of the impregnated eggs takes place, when, passing from the ovary into the oviduct, they are conducted by means of the ovipositor, in which it terminates, to their proper situation. By far the greater number of insects extrude them singly, a longer interval elapsing between the passage of each egg in some than in others. In those tribes which place their eggs in groups, such as most butterflies and moths, and many beetles, they pass from the ovaries usually with great rapidity; while in the Ichneumonidæ, Sphegidæ, Œstri, and other parasitic genera, which usually deposit their eggs singly, an interval of some minutes, hours, or perhaps even days, intervenes between the extrusion of each egg. One remarkable instance of the former mode I noticed in my letter on the Perfect Societies of Insects[87]; another may be cited, to which you may yourself be a witness—I allude to that common moth, vulgarly called the Ghost (Hepialus Humuli), which lays a large number of minute black eggs, resembling grains of gunpowder, and ejects them so fast that, according to De Geer, they may be said to run from the oviduct, and are sometimes expelled with the force of a popgun[88]. A Tetrapterous insect, the genus of which is uncertain, is said, when it is taken, to discharge its eggs like shot from a gun[89]. And a friend of mine, who had observed with attention the proceedings of a common crane-fly (Tipula),[Pg 67] assured me that several females which he caught projected their eggs to the distance of more than ten inches.

A few Diptera extrude them in a sort of chain or necklace, each egg being connected by a glutinous matter with that which precedes and follows it. In a small species of a genus allied to Psychoda (a kind of midge), which one season was abundant in a window of my house, this necklace is composed of eggs joined by their sides, not unlike those strung by children of the seeds of the mallow[90]. Other Tipulidæ on the contrary extrude their eggs joined end to end, so as to resemble a necklace of oval beads. Beris clavipes and Sciura Thomæ, two other flies, produce a chain about an inch long, consisting of oval eggs connected, in an oblique position, side by side; an arrangement very similar prevails in the ribband of eggs which drop from some of the Ephemeræ[91].

These eggs, like those of the insects first mentioned, though connected, are expelled in succession; but other tribes, as the Libellulidæ, with the exception of Agrion, many Ephemeræ, Trichopterous insects, &c. expel the whole at once, as it were in a mass. In those first mentioned they are gummed together in an oblong cluster[92]. In one Ephemera mentioned by Reaumur[93], they formed two oblong masses, each containing from three to four hundred eggs, and three and a half or four lines long. These animals as soon as their wings are developed eject these masses by two orifices, and are aided in the process by two vesicles full of air, wherever they happen to alight or to fall; in most instances it is the water, their proper element, that receives them, but the animal does not appear to know the difference between a solid and a liquid,[Pg 68] and seems only anxious how to free herself from a burthen that oppresses her; all has been contrived that an insect so short-lived may finish her different operations with the utmost celerity: the term of her existence would not have admitted the leisurely extrusion of such a number of eggs in succession[94]. Some Trichoptera, or May-flies, as Phryganea grandis L., exclude their eggs in a double packet, enveloped in a mass of jelly, (a circumstance often attending the eggs that produce aquatic larvæ,) upon the leaves of willows[95]. A similar double packet in the year 1810 I observed appended to the anus of a black species with long antennæ, probably Phryganea atrata F.[96] Upon taking several of the females I was surprised to find in the above situation a seemingly fleshy substance of a dirty yellow. At first, from its annular appearance, I conceived it to be some parasitic larva, but was not a little surprised upon pulling it away that it was full of globular transparent dusky eggs: it was about two lines and a quarter in length and nearly one in breadth. Being bent double it was attached to the animal by the intermediate angle, and when unfolded was constricted in the middle[97]. Each half, which was roundish, had about ten sharp transverse ridges, the interstices of which appeared as if crenated, an appearance produced by the eggs which it contained. Upon more than gentle pressure it burst and let out the eggs. Though resembling the packet of P. grandis in shape and other circumstances, it was nothing like[Pg 69] jelly, but had rather a waxy appearance, and seems to have been covered by a membrane: so that the excluded larvæ must probably have eaten their way out of it. I have still by me, in 1822, specimens of these egg-packets, which, after the lapse of so many years, retain their original form and colour. It is not improbable that other species extrude their eggs in a similar case. Scopoli says of P. bicaudata L., that the female carries about under her belly her eggs united into a globe, like Lycosa saccata[98]. The eggs of Geometra Potamogata F. are also enveloped in a gelatinous substance, and the mass is covered with leaves[99].

Insects of the Diptera order also, like frogs and toads, commit their eggs to the water imbedded in masses of jelly. Dr. Derham describes two different kinds of them, in one of which the eggs were laid in parallel rows end to end, and in another in a single row, in which the sides were parallel[100]. But the most remarkable and beautiful specimen of this kind that I ever saw was one that, many years ago, I took out of a pond at Wittersham in Kent, from which I requested a young lady to make the drawing I send you[101]. The mass of jelly, about an inch and a quarter long, and rather widest in the middle, was attached by one end to some aquatic grass, and from one end to the other ran a spiral thread of very minute eggs, the turns of the screw being alternately on each side.

The mode of exclusion of the eggs of the Blattæ, which are engaged for a whole week in the business of oviposition, is very singular: the female deposits one or two large suboviform capsules, as large as half their abdomen, rounded on one side, and on the other straight and serrated,[Pg 70] which at first is white and soft, but soon becomes brown and hard. This egg-case, as it may be called, contains sixteen or eighteen eggs arranged in a double series, and the cock-roaches when hatched make their escape through a cleft in its straight side, which shuts so accurately when they have quitted it, that at first it appears as entire as before[102]. The insects of the genus Mantis also, or what are called the praying insects, when they deposit their eggs, eject with them a soft substance, which hardens in the air and forms a long kind of envelope resembling parchment, in which the eggs are arranged also in a double series. And the Locusts (Gryllus Locusta L.) are said by Morier[103] to deposit in the ground an oblong substance, of the shape of their abdomen, which contains a considerable number of eggs arranged neatly in rows. The peristaltic motion observed in the females of some insects during oviposition has been before described[104].

ii. Situation. Under this head I include the situation in which the female insect places her eggs when extruded, whether she continues her care of them and carries them about till they hatch, or whether she entirely deserts them, placing them either without a covering within reach of their food, or enveloping them in hair or otherwise protecting them from accident or the attack of enemies. I shall consider them under two views: first, as depositing their eggs in groups, whether covered or naked; and secondly, as depositing them singly.

[Pg 71]

1. Those that deposit their eggs in groups are first to be considered. I shall begin with those that protect them with some kind of covering.

I have already mentioned in a former letter[105] the silken bag with which Lycosa saccata Latr., a kind of spider, surrounds her eggs, and in which she constantly carries them about with her, defending them to the last extremity. Many other spiders, indeed nearly the whole tribe, fabricate similar pouches, but of various sizes, forms, texture, and colours. Some are scarcely so big as a pea, others of the size of a large gooseberry; some globular, some bell-shaped; others, the genus Thomisus Walck. in particular, depressed like a lupine; some of a close texture like silk; others of a looser fabric resembling wool: some consisting of a single pellicle, but most of a double, of which the interior is finer and softer[106]; some white; others inclining to blue; others again yellow or reddish; most of them are of a whole colour, but that of Epeira fasciata is gray varied with black[107]. And while the parent spider of some kinds (the Lupi) always carries her egg-bag attached to her anus, others hold them by their palpi and maxillæ; and others suspend them by a long thread, or simply fasten them in different situations, either constantly remaining near them (the Telariæ), or wholly deserting them (the Retiariæ). The eggs of one of these last Lister describes as often fixed in a very singular situation—the cavity at the end of a ripe cherry; and thus, as he expresses it—"Stomachi maxime delicatuli quoties hanc innocuam buccam non minus ignoranter quam avide devorarunt[108]."

[Pg 72]

Herman informs us, that the species of the genus Chelifer carry their eggs in a mass under their belly[109].

Madam Merian gives an account of two species of Blatta, which she affirms carry an egg-pouch about with them—one species (B. gigantea?) she describes as carrying its eggs in a globular pouch of web like certain spiders, and the other in a brown bag, which, when alarmed, it drops and makes off[110]. But this admirable paintress of natural objects was not always correct in her statements[111]: it seems very improbable, from the habits of those species of which we know the history, that any of them should spin a pouch of web for their eggs.

The only insects certainly known to spin an egg-pouch like the spiders, are the Hydrophili, a kind of water-beetles. Some of these, as H. lividus, carry them about with them, like Lycosa saccata, attached to the under side of their body, as M. Miger observed[112]; and others when they are finished desert them. That of the great water-beetle (Hydrophilus piceus) was long ago described and figured by Lyonnet[113]; and a more detailed account of it has since been given by M. Miger[114]. In form it somewhat resembles a turnip when reversed, since it consists of a pouch of the shape of an oblate spheroid, the great diameter of which is three quarters of an inch; and the small, half an inch, from which rises a curved horn, about an inch long and terminating in a point[115]. The animal is furnished with a pair of anal spinners, which move from right to left, and up and down, with[Pg 73] much quickness and agility: from these spinners a white and glutinous fluid appears to issue, that forms the pouch, which it takes the animal about three hours to construct. The exterior tissue is produced by a kind of liquid and glutinous paste, which by desiccation becomes a flexible covering impermeable to water; the second, which envelops the eggs, is a kind of light down of great whiteness, that keeps them from injuring each other. The tissue of the horn is of a silky nature, porous and shining, and greatly resembling the cocoons of Lepidoptera. This part, contrary to what Lyonnet supposes, appears calculated to admit the air, the water soon penetrating it when submerged. At its base is the opening prepared for the egress of the larvæ, when hatched, which is closed by some threads, that, by means of the air confined in the cocoon or pouch, hinder the water from getting in[116]. This nidus does not float at liberty in the water till after the eggs are hatched, the parent animal always attaching it to some plant. By means of this anomalous process for a beetle, which this insect is instructed by Providence thus to perfect, the precious contents of its little ark are secured from the action of the element which is to be the theatre of their first state of existence, from the voracity of fishes, or the more rapacious larvæ of its own tribe, until the included eggs are hatched, and emerge from their curious cradle.

I shall next amuse you with a few instances, in which the Allwise Creator instructs the parent insect, instead of defending her eggs with a covering furnished by her internal organs, to provide it from without, either from[Pg 74] her own body or from some other substance. Most commonly, indeed, the female leaves her cluster of eggs without any other covering than the varnish with which in this case they are usually besmeared. Either they are deposited in summer and will soon be hatched, or they are of a substance calculated to encounter and resist the severities of the season. But many species, whose eggs are more tender or have to resist the cold and wet of winter, defend them in the most ingenious manner with a clothing of different kinds of substance.

Cassida viridis, a tortoise beetle, Rösel tells us, covers her group of eggs with a partially transparent membrane. Arctia Salicis F., a moth, common on willows, wholly conceals hers with a white frothy substance, which when dry is partly friable and partly cottony, and being insoluble in water effectually protects them from the weather[117]. The female of Lophyrus Pini (a saw-fly), having by means of her double saw made a suitable longitudinal incision in the leaf of a fir, and placed in it her eggs in a single row end to end, stops it up with a green frothy fluid mixed with the small pieces of leaf detached by her saws, which when dry becomes friable: a necessary precaution, since these eggs are extremely brittle[118]. Arctia chrysorhœa, Hypogymna dispar, and several other moths, surround theirs with an equally impervious and more singular clothing—hair stripped from their own bodies. With this material, which they pluck by means of their pincer-like ovipositor, they first form a soft couch on the surface of some leaf: they then place upon it successively layers of eggs, and surround them with a similar downy coating, and when the whole number is deposited cover[Pg 75] the surface with a roof of hairs, which cannot be too much admired; for those used for the interior of the nest are placed without order, but those employed externally are arranged with as much art and skill as the tiles of a roof, and as effectually keep out the water, one layer resting partly on the other, and all having the same direction, so that the whole resembles a well-brushed piece of shaggy cloth or fur. When the mother has finished this labour, which often occupies her for twenty-four hours, and sometimes even twice that period, her body, which before was extremely hairy, is almost wholly naked—she has stripped herself to supply clothing to her offspring, and having performed this last duty she expires. The female moths which thus protect their eggs are often furnished with an extraordinary quantity of hair about the anus for this express purpose; and Reaumur conjectures, that the singular anal patch of scales resembling those of the wings, but considerably larger, which is found in the female of Lasiocampa Pityocampa, is destined for the same purpose[119].

Reaumur had once brought to him a nidus of eggs clothed still more curiously: they surrounded a twig in a spiral direction, like those of Lasiocampa Neustria, but were much more numerous, and were thickly covered with fine down, not pressed close, but standing off horizontally, which assumed much the same appearance as a fox's tail would if twisted spirally round a branch[120].

A procedure nearly similar was observed by De Geer in some species of Aphides (A. Alni and A. Pruni), which covered their eggs with a white cottony down detached[Pg 76] from their belly by means of their hind legs[121]. In this case, however, the eggs were separately coated with the down, but there was no general covering to the group.

Several insects make the leaves and other parts of plants serve as coverings for their eggs. Tenthredo Rosæ L., a saw-fly, and other species of the same genus, with their saws make an incision in the green twigs of shrubs and trees, and fill it with a line of eggs placed end to end, taking care that, as the eggs grow after they are laid, they are placed at such distances as to leave room for their expansion[122]. Rhynchites Bacchus, a brilliant weevil, well known to the vine-dressers for the injury it does[123], rolls with much art the leaves of the vine, so as to form a cavity, in which it places its eggs; other species practise similar manœuvres; and some probably place their young progeny in the interior of twigs, making an opening for that purpose with their rostrum—at least, I once saw Rhynchites Alliariæ L. with its rostrum plunged up to the antennæ in the twig of a crab-tree. Others of this tribe, as we know, place their eggs in the interior of fruits and grain, as the nut, acorn, and common weevils.

It is probable that most of the above coverings serve another purpose besides the protection of the eggs from wet and cold—that of sheltering them from the action of too great light, which, as Dr. Michellotti by numerous experiments has ascertained, is fatal to the included germe[124]. On this account it is perhaps that so many insects fasten their eggs to the under side of leaves. Those[Pg 77] exposed in full day have usually an opaque and horny texture.

Some insects are spared all trouble in providing a covering for their eggs, their own bodies furnishing one in every respect adapted to this purpose. Not to mention the Onisci, or wood-lice, since they rather belong to the Crustacea, which have a four-valved cell under the breast, in which they carry their eggs, as the kangaroo does its young in its abdominal pouch, the whole body of the female of those strange animals the Cocci becomes a covering for her eggs, which it incloses on every side. To make this intelligible to you, further explanation is necessary. You must have noticed those singular immovable tortoise-shaped insects, which are such pests to myrtles and other greenhouse plants. These are the young of a species of Coccus (C. Hesperidum L.), and their history is that of the whole race. Part of them never become much bigger than the size of which you ordinarily see them, and when full-grown disclose minute two-winged flies, which are the males. The size of the females, which glue themselves to a twig or leaf as if lifeless, now augments prodigiously, and the whole body, distended with the thousands of eggs which it includes to the bigness of a large pea, without any vestige of head or limb, resembles a vegetable excrescence or gall-apple rather than an insect. If you remove one of them, you will perceive that the under part of its abdomen is flat and closely applied to the surface of the branch on which it rests, only a thin layer of a sort of cotton being interposed between them. In laying her eggs the female Coccus does not, like most insects, protrude them beyond her body into day-light; but as soon as the first egg has passed the orifice of her[Pg 78] oviduct, she pushes it between her belly and the cottony stratum just mentioned, and the succeeding eggs are deposited in the same manner until the whole are excluded. You will ask how there can be found space between the insect's belly and the cotton, to which at first it was closely applied, for so large a mass of eggs? To comprehend this, you must consider that nearly the whole contents of its abdomen were eggs; that in proportion as these are extruded a void space is left, which allows the skin of the under side of the body to be pushed upwards, or towards that of the back, affording room between it and the cottony web for their convenient stowage. If you examine the insect after its eggs are all laid, you will find that they have merely changed their situation; instead of being on the upper side of the skin forming the belly, and within the body, they now are placed between it (now become concave and nearly touching the back) and the layer of cotton. As soon as the female Coccus has finished her singular operation she dies; but her body, retaining its shape, remains glued upon the eggs, to which it forms an arched covering, effectually protecting them, until they are hatched, from every external injury. Some species lay so many eggs, that the abdomen is not sufficiently large to cover the whole mass, but merely one side of it, the remainder being enveloped in cottony web[125].

I am next to consider the situation of those eggs that are excluded by the mother in groups without any other covering than the varnish with which they are usually besmeared in their passage from the oviduct. The females[Pg 79] only place them upon or near the food appropriated to the young larvæ, to which they adhere by means of the varnish just mentioned. These groups consist of a greater or less number; and when the eggs are hatched by the heat of the sun, the larvæ begin to disperse and attack with voracity the food that surrounds them. It is thus that most butterflies and moths attach their eggs to the stems, twigs, and leaves of plants; that the lady birds (Coccinellæ), the aphidivorous flies (Syrphi &c.), and the lace-winged flies (Hemerobii), deposit them in the midst of plant-lice (Aphides); that the eggs of some flesh-flies are gummed upon flesh; those of crickets and grasshoppers buried in the earth; those of gnats and other Tipulidans set afloat upon, or submerged in, the water.

Frequently the whole number of eggs laid by one female is placed in one large group, more commonly, however, in several smaller ones, either at a distance from each other on the same plant, or on distinct plants. The object in the latter case seems to be, in some instances, to avoid crowding too many guests at one table, in others to protect the unhatched eggs from the voracity of the larvæ first excluded, which would often devour them if in their immediate neighbourhood.

In the disposition of the eggs which compose these groups much diversity prevails. Sometimes they are placed without order in a confused mass: more frequently, however, they are arranged in different, and often in very beautiful modes. The common cabbage-butterfly (Pieris Brassicæ) and many other insects place theirs upon one end, side by side, so as, comparing small things with great, to resemble a close column of soldiers, in consequence of which those larvæ which, on[Pg 80] hatching, proceed from the upper end, cannot disturb the adjoining eggs. Many indeed have a conformation purposely adapted to this position, as the hemisphærical eggs of the puss-moth (Cerura Vinula), which have the base by which they are gummed membranous and transparent, while the rest is corneous and opaque. The same ready exit to the larva is provided for in the oblong eggs of the emperor moth (Saturnia Pavonia), which are piled on their sides in two or more lines like bottles of wine in a bin[126].

Where the larva does not emerge exactly from the end of the egg other arrangements take place. The whirlwig-beetle (Gyrinus natator) and the saw-fly of the gooseberry &c. (Tenthredo flava L.) dispose theirs end to end in several rows; the former upon the leaf of some aquatic grass, the rows being parallel[127], the latter gummed to the main nerves of gooseberry or currant leaves, the direction of which they follow[128].

But the lackey-moths (Lasiocampa Neustria, castrensis, &c.) adopt a different procedure. As their eggs, which are laid in the autumn, are not to be hatched until the spring, the female does not, like most other moths, place them upon a leaf, with which they might be blown by the winter's storms far from their destined food, but upon the twig of some tree, round which she ranges them in numerous circles. If you examine your fruit-trees, you can scarcely fail to find upon the young twigs collections of these eggs, which are disposed with such admirable art, that you would take them rather for pearls, set by the skilful hand of a jeweller, than for the eggs of[Pg 81] an insect. Each of these bracelets, as the French gardeners aptly call them, is composed of from 200 to 300 pyramidal eggs with flattened tops[129], having their axes perpendicular to the circumference of the twig to which they are fastened, surrounding it in a series of from fifteen to seventeen close spiral circles, and having their interstices filled up with a tenacious brown gum, which, while it secures them alike from the wintry blast and the attack of voracious insects, serves as a foil to the white enamel of the eggs that it encompasses. It is not easy to conceive how these moths contrive to accomplish so accurately with their tail and hind feet an arrangement which would require nicety from the hands of an artist; nor could Reaumur, with all his efforts and by any contrivance, satisfy himself upon this head. He bred numbers of the fly from the egg, and supplied the females after impregnation with appropriate twigs; but these, as though resolved that imprisonment should not force from them the secret of their art, laid their eggs at random, and made no attempt to place them symmetrically[130].

This illustrious Entomologist was more successful in discovering the mode in which another insect, the common gnat, whose group of eggs is, in some respects, as extraordinary as that last described, performs its operations. The eggs of this insect, of a long phial-like form, are glued together, side by side, to the number of from 250 to 300, into an oblong mass, pointed and more elevated at each end, so as considerably to resemble a little boat in shape. You must not here suppose that I use the term boat by way of illustration merely; for it has all the essential properties of a boat. In shape it[Pg 82] pretty accurately resembles a London wherry, being sharp and higher, to use a nautical phrase, fore and aft; convex below and concave above; floating, moreover, constantly on the keel or convex part. But this is not all. It is besides a life-boat, more buoyant than even Mr. Greathead's: the most violent agitation of the water cannot sink it; and what is more extraordinary, and a property still a desideratum in our life-boats, though hollow it never becomes filled with water, even though exposed to the torrents that often accompany a thunder-storm. To put this to the test, I yesterday (July 25, 1811) placed half a dozen of these boats upon the surface of a tumbler half full of water; I then poured upon them a stream of that element from the mouth of a quart bottle held a foot above them. Yet after this treatment, which was so rough as actually to project one out of the glass, I found them floating as before upon their bottoms, and not a drop of water within their cavity.

This boat, which floats upon the surface of the water until the larvæ are disclosed, is placed there by the female gnat. But how? Her eggs, as in other insects, are extruded one by one. They are so small at the base in proportion to their length that it would be difficult to make them stand singly upright on a solid surface, much more on the water. How then does the gnat contrive to support the first egg perpendicularly until she has glued another to it—these two until she has fixed a third, and so on until a sufficient number is fastened together to form a base capable of sustaining them in their perpendicular position? This is her process. She fixes her four anterior legs upon a piece of leaf, or a blade of grass, and projects her tail over the water. She[Pg 83] then crosses her two hind legs, and in the inner angle which they form, retains and supports the first laid egg, as it proceeds from the anus. In like manner she also supports the second, third, &c., all of which adhere to each other by means of their glutinous coating, until she feels that a sufficient number are united to give a stable base to her little bark; she then uncrosses her legs, and merely employs them to retain the mass until it is of the required size and shape, when she flies away, and leaves it to its fate floating upon the water[131].

It may not be out of place to mention here a remarkable circumstance which not seldom attends a kind of water-scorpion (Naucoris F.) occasionally to be met with in collections of Chinese insects. Its back is often covered with a group of rather large eggs, closely arranged; but whether these are its own eggs or those of some large species of water-mite (Hydrachna Maïll.) has not been clearly ascertained. On the former supposition, the ovipositor must be remarkably long and flexile to enable the animal to place the eggs on its back. In confirmation of the latter it may be observed, that the species of the genus Hydrachna usually attach their eggs to the body and legs of aquatic insects, as for instance H. abstergens to the water-scorpion (Nepa cinerea), &c.[132]

2. After having thus laid before you some of the procedures of those insects that usually deposit their eggs in groups, either naked or defended by coverings of various kinds, I next proceed to a rapid survey of those of the species that commonly deposit them singly. Some[Pg 84] of these, as for instance the Admiral Butterfly (Vanessa Atalanta), glue each egg carefully to its destined leaf by alighting on it for a moment. Another butterfly (Hipparchia Hyperanthus) whose caterpillar is polyphagous, drops hers at random on different plants. In general it may be observed, that all those larvæ which live in solitude, as in the interior of wood, leaves, fruits, grain, animals, &c., proceed from eggs laid singly by the female, which is usually provided with an appropriate instrument for depositing them in their proper situation. Thus the nut-weevil (Balaninus Nucum Germ.) and also that of the acorn (B. Glandium) pierce a nut or an acorn with their long beak, and then deposit in the hole an egg, from which proceeds the maggot that destroys those fruits. Leeuwenhoek asserts that the common weevil (Calandra granaria) adopts the same process, boring a hole in every single grain of corn before it commits an egg to it, and at the same time, by this manœuvre, prepares a small quantity of flour to serve for the food of the tender grub when it is first hatched[133]. It is probable that the Rhyncophorous or weevil tribe in general chiefly use their beaks for the purpose of depositing their eggs in different vegetable substances, and perhaps principally in fruit or grain. The tribe of gall-flies (Cynips) on the contrary, whose economy, detailed in a former letter[134], interested you so much, bore an opening for the egg with their spiral oviduct, which also conveys it.

Another large tribe of insects depositing their eggs singly, are those which feed upon the bodies of other animals, into the flesh of which they are either inserted, or placed so as speedily to find their way into it. Some[Pg 85] of these introduce them into living animals, and then leave them to their fate, as the Ichneumons and gad-flies: others deposit them along with the dead body of an insect interred in a hole, often prepared with great labour, as the different species of sand-wasps (Sphecidæ), spider-wasps (Pompilidæ), &c.: the manners of the latter of these tribes have been already adverted to[135], and those of the Ichneumonidæ will come more fully under consideration when I treat of the diseases of insects.

A similar labour in providing suitable habitations for their eggs is undergone by various other insects whose larvæ live chiefly on vegetable food, some inserting their egg within the substance the larva devours, as those that prey on timber, twigs, roots, or the like, and others on its surface. One would suppose at first, that the exceedingly small egg which produces the subcutaneous larvæ would, by the parent moth, be imbedded in the substance of the leaf which is to exhibit hereafter their serpentine galleries: but this is not the case, for she merely glues it on the outside; at least such was the situation of the only egg of these very minute moths Reaumur had ever an opportunity to observe[136].

Other insects, belonging to the tribe which lay their eggs singly, bury them in the ground. Of this description are many of the lamellicorn insects, the dung-chafers (Scarabæidæ MacLeay) particularly, which, inclosing their eggs in a pellet of dung, deposit them in deep cylindrical cavities. Concerning the proceedings of some of these, as well as of the whole race of bees, wasps, &c., which all lay single eggs, I have before detailed to you[Pg 86] many interesting particulars[137]. I must not conclude this subject without observing, that the female Pycnogonidæ, an osculant tribe between Insects and Crustacea, carry their eggs upon two pair of false legs[138].

iii. Substance. From this long dissertation on the situation of the eggs of insects and matters connected with it, I pass on to their substance or their external and internal composition, giving at the same time some account of the embryo included in them. The eggs of insects, like those of birds, consist in the first place of an external coat or shell, varying greatly, as to substance, in different genera. Most commonly, particularly in those which deposit their eggs in moist situations, as in dung, earth, and the like, it is a mere membrane, often thin and transparent, and showing, as in spiders, all the changes that take place in the inclosed embryo, as the formation of the head, trunk, and limbs[139]. This membrane is sometimes so delicate as to yield to the slightest pressure, and insufficient to protect the included fluids from too rapid an evaporation, if the eggs be exposed to the full action of the atmosphere. In most Lepidoptera, and several other tribes, this integument is considerably stronger, in those moths whose eggs are exposed throughout the winter, as Lasiocampa Neustria, &c., so hard as not to yield easily to the knife. Even in these, however, its substance is more analogous to horn or a stiff membrane than to the shell of the eggs of birds. Nothing calcareous enters into its composition, and it is not perceptibly acted upon by diluted sulphuric[Pg 87] acid. The eggs of birds are lined by a fine membrane; but I have examined several of those of insects, and have been able to discover nothing of the kind in them. I will not, however, affirm that it does not exist, though the shell of the insect egg appears more analogous to the membrane that lines that of the bird than to the outside shell itself.

Within this integument is included a fluid, on the precise nature of which, except that it is an aqueous whitish fluid, few or no observations have been made, or indeed are practicable; but it is reasonable to suppose, that like the white and yolk of the bird's egg, it serves for the development of the organs of the germe of the future insect.

But few observations are recorded that relate to the embryo included in the egg. It is stated, that it is invested with an extremely fine and delicate pellicle—supposed by some analogous to the Chorion and Amnios of the human fœtus, though others think the shell of the egg to correspond with the Chorion, and the successive integuments of the larva with the Amnios[140]. When the egg is first laid, nothing indeed is to be seen in it but the fluid just mentioned; the first change in this fluid is the appearance of the head of the embryo, more particularly in Coleoptera, of two points, the rudiments of the mandibles, and of those apertures into the tracheæ which I have called spiracles[141]; the little animal we may suppose[Pg 88] then assumes its form and limbs. The embryo is usually so folded in the egg that the head and tail meet[142], and the head, annuli, and other parts of the larva are often visible through the shell[143]. Swammerdam even saw the pulsation of the great dorsal vessel through the shell of the egg of Oryctes nasicornis.

Under this head I must notice another singular circumstance peculiar I believe to the eggs of insects, that sometimes, though rarely, they are covered with down or hair. Those of a singular little hemipterous insect, of a genus I believe at present undescribed, the ravages of which upon the larch have been before noticed[144], are covered by a downy web, as is the case with the animal itself. De Geer has described the eggs of a bug, not uncommon in this country (Pentatoma juniperina Latr.), which are reticulated with black veins, in which very short bristles are planted[145]. I possess also a nest of brown eggs, probably of a species of the same genus, found upon furze, which appear to be covered with very short downy hairs. The top of these is flat, and surrounded by a coronet of short bristles, each surmounted by a small white ball, so as to wear the appearance of a beautiful little Mucor. But hairy eggs are not confined to the Hemiptera Order, for, according to Sepp, those of the figure-of-eight moth (Bombyx cæruleocephala) are of this description[146].

iv. Number. The fertility of insects far exceeds that of[Pg 89] birds, and is surpassed only by that of fishes[147]. But the number of eggs laid by different species, sometimes even of the same natural family, is extremely various. Thus the pupiparous insects may be regarded as producing only a single egg; Musca Meridiana L., a common fly, lays two[148], other flies six or eight; the flea twelve; the burying beetle (Necrophorus Vespillo[149]) thirty; May-flies (Trichoptera K.) under a hundred; the silk-worm moth about 500; the great goat-moth(Cossus ligniperda) 1,000; Acarus americanus more than 1,000[150]; the tiger-moth (Callimorpha Caja) 1,600; some Cocci 2,000, others 4,000; the female wasp at least 30,000[151]; the queen bee varies considerably in the number of eggs that she produces in one season, in some cases it may amount to 40,000 or 50,000 or more[152]; a small hemipterous insect, resembling a little moth (Aleyrodes proletella Latr.) 200,000. But all these are left far behind by one of the white ants (Termes fatale F. bellicosus Smeath.)—the female of this insect, as was before observed[153], extruding from her enormous matrix not less than 60 eggs in a minute, which gives 3,600 in an hour, 86,400 in a day, 2,419,200 in a lunar month, and the enormous number of 211,449,600 in a year: probably she does not always continue laying at this rate; but if the sum be set as low as possible, it will exceed that produced by any other known animal in the creation.

v. Size. The size of the eggs is in proportion to that of[Pg 90] the insect producing them, though in some instances small ones produce larger eggs than those laid by bigger species. Thus the eggs of many Aptera, as those of that singular mite Uropoda vegetans, and of the bird-louse found in the golden pheasant, are nearly as large, it is probable, as the parent insect; while those of the ghost-moth (Hepialus Humuli) and many other Lepidoptera, &c. are vastly smaller. This circumstance perhaps depends principally on the number they produce: the majority of them, however, are small. The largest egg known, if it be not rather an egg-case, is that of a spectre insect (Phasma dilatatum), figured in the Linnean Transactions[154], being five lines in length and three in width, which probably approaches near the size of that of some humming-birds. The largest egg of any British insect I ever saw was that of the common black rove-beetle (Staphylinus olens) sent me by Mr. Sheppard—this is a line and half long by a line in width. But we do not often meet with insect-eggs exceeding a line in length. A vast number are much smaller: those of Ephemeræ are more minute than the smallest grains of sand[155], and some almost imperceptible, as those of the subcutaneous moths, to the naked eye. Commonly the eggs laid by one female are all of the same size; but in several tribes, those containing the germe of the female are larger than those that are to give birth to a male. This appears to be the case with those of the Rhinoceros beetle (Oryctes nasicornis[156]), and according to Gould with those of ants[157]. As the female in a vast number of instances is much bigger than the male, it is not improbable that this law may hold[Pg 91] very extensively. It is stated, however, by Reaumur[158], that the reverse of this takes place in the eggs of the hive-bee, those that are to produce males being larger than the rest.

Another peculiarity connected with the present head is the augmentation in bulk which takes place, after exclusion, in the eggs of the great tribe of saw-flies (Tenthredo L.), the gall-flies (Cynips L.), the ants (Formica L.) and the water-mites (Hydrachna Maïll. Atax F.). Those of the two former, which are usually deposited in the parenchymous substance of the leaves, or of the young twigs, of various plants, imbibe nutriment in some unknown manner, through their membranous skins, from the vegetable juices which surround them[159], and when they have attained their full size are nearly twice as large as when first laid. Except in the eggs of fishes, whose volume in like manner is said to augment previously to the extrusion of the young, there is nothing analogous to this singular fact in any other of the oviparous tribes of animals, the eggs of which have always attained their full size when they are laid.

It is to M. P. Huber that we are indebted for the knowledge of the fact that the eggs of ants grow after being laid, a circumstance favoured probably by the moist situation in which the workers are always careful to keep them. By an accurate admeasurement he found that those nearly ready to be hatched were almost twice as big as those just laid[160]. A similar observation was made on the red eggs of a water-mite (Hydrachna abstergens) by Rösel, who conjectured that they draw their means of increase from the body of the water-scorpions[Pg 92] (Nepæ), of which they form so singular an appendage[161], which opinion is confirmed by De Geer, who observes that when the water-scorpions are covered by an unusual number of the eggs of the water-mites, they grow weak and languid, and endeavour to rid themselves of their parasitic appendages[162]. It is most probable that the mite lately named (Uropoda vegetans), which is often found planted as it were upon the bodies of various beetles, by means of a long pedicle, through which, as the fœtus by an umbilical chord and placenta, it derives its nutriment from the above animals, is at first so fixed in the egg state, though before it is disengaged from the pedicle it is hatched, since it is often found with its legs displayed and quite active—this is the more probable, as the eggs of the water-mite are fixed by a pedicle to the animals to which they are attached[163]. I have met with a remarkable instance, in which pedunculated eggs seem to draw nutriment from the mother, which brings the pedicle still near to the nature of the umbilical chord. Those of the small hemipterous insect which infests the larch before alluded to, are attached to the anal end of the mother by a short foot-stalk not longer than the egg.

Dr. Derham seems to have observed, that the eggs of some Diptera, of the tribe of Tipulidæ, also increase in size before the larva is excluded[164]. It seems to me likely enough, that in this and many of the above cases in which the egg is supposed to grow, it is rather an extension of the flexile membrane that forms their exterior proportioned to the growth of the included embryo from food[Pg 93] it finds within the egg, than from any absorption from without.

vi. Shape. We are accustomed to see the eggs of different species of oviparous animals so nearly resembling each other in form, that the very term egg-shaped has been appropriated to a particular figure. Amongst those of birds, with which we are most familiar, the sole variations are shades of difference between a globular and oval or ovate figure. The eggs of insects, however, are confined by no such limited model. They differ often as much, both as to their shape, sculpture, and appendages, as one seed does from another; and it is not improbable that, if duly studied, they would furnish as good indications of generic distinctions as Gærtner has discovered in those of plants. Their most usual form indeed is globular, oval, or oblong, with various intermediate modifications. We meet with them ovate, or of the shape of the common hen's egg, flat and orbicular, elliptical, conical, cylindrical, hemispherical, lenticular, pyramidal, square, turban-shaped, pear-shaped, melon-shaped, boat-shaped, of the shape of an ale-stand, of a drum, &c.[165], and sometimes of shapes so strange and peculiar, that we can scarcely credit their claim to the name of eggs. Thus the eggs of the gnat are oblong and narrow, or nearly cylindrical, having at the top a cylindrical knob[166], so as to give them the precise form of the round-bottomed phial sometimes used by chemists: those of the common[Pg 94] water-scorpion (Nepa cinerea) are oblong, and at the upper end are surrounded by a sort of coronet, consisting of seven slender rays or bristles of the length of the egg[167], so as to resemble somewhat the seeds of Carduus benedictus (Cnicus acarna[168]) of the old botanists. One would think this spinous circlet a very awkward appendage to bodies which are to be gradually extruded through the fine membranous ovaries and oviduct which inclose them: but they are so admirably packed, the unarmed end of each egg fitting closely into the space inclosed by the spines of the one next below it, or, rather, the spines which are moveable, embracing it closely, that not only is no room lost, but the ovaries are perfectly secure from injury. The eggs of another species of this tribe (Ranatra linearis) have only two of these spines or bristles—they are inserted in the stem of a water-rush (Scirpus) or other aquatic plant, so as to be quite concealed, and are only to be detected by the two bristles which stand out from it[169]. The eggs of the beautiful lace-winged flies (Hemerobius), those golden-eyed insects so serviceable in destroying the plant-lice (Aphides[170]), are still more singular. Those of H. Perla are oval, and each of them attached to a filiform pedicle not thicker than a hair, and seven or eight times as long as the egg. By this pedicle (which is supposed to be formed by a glutinous matter attached to one end, which the female draws out by abstracting her ovipositor with the egg partly in it[Pg 95] from the leaf, to which she has previously applied it, to a proper length, when the gluten becoming sufficiently solid she wholly quits the egg,) the eggs are planted in groups of ten or twelve on the surface of leaves and twigs, from which they project like so many small fungi, to some of which they have a remarkable resemblance. When the included larva has made its way out of them by forcing open the top, they look like little vases, and were actually once figured by a Naturalist, as we learn from Reaumur, as singular parasitic flowers growing upon the leaves of the elder, for the origin of which he was extremely puzzled to account[171]. Eggs similarly furnished with a pedicle are also laid by other insects; but as most of these have been before alluded to, it is not necessary to describe them here[172]. The cause of these differences of form is for the most part concealed from us: in many instances it may perhaps be referred to that will to vary forms, and so to glorify his wisdom[173] and power, independently of other considerations, which, as Dr. Paley has well remarked[174], seems often to have guided the Great Author of Nature. But in some cases the end to be answered is sufficiently evident. The long footstalks of the eggs of the Hemerobius just mentioned, there can be little doubt, are meant to place them out of the reach of the hosts of predaceous insects which roam around them, from whose jaws, thus elevated on their slender shaft, they are as safe as the[Pg 96] eggs of the tailor bird in its twig-suspended nest from the attack of snakes. Reaumur has described the eggs of a kind of fly, common upon the excrements of the horse and other animals (Scatophaga vulgaris Latr.), or one related to it, that requires to be immersed in the dung to which it is committed, on which the future grubs are to feed. He found that if not thus surrounded with moisture, they infallibly shrivelled up and came to nothing; but it is equally necessary that they should not be wholly covered: if they were, the young larva would be suffocated at its first exit from the egg. In what way is this nice point secured? In this manner. Each egg is provided at its upper end, at which the animal when hatched comes out, with two diverging horns[175]; these prevent it from being stuck into the excrement, in which the female deposits the eggs one by one, more than three-fourths of its length: and when examined they resemble not badly, as Reaumur remarks (except that their colour is white), a parcel of cloves stuck into a pudding, as they are neatly inserted at due distances in the disgusting mass[176]. The French Naturalists found these eggs in swine's dung; I have observed them in cow-dung. Latreille thinks that the bristles above described attached to the eggs of Nepa and Ranatra have a similar use, as the female plunges them all but these bristles into the stems of aquatic plants[177]: but may not this have something to do with their oxygenation? Reaumur has figured another egg of a dipterous insect which has a longitudinal wing or lateral margin attached to it, giving[Pg 97] it the form of an oblong square, the object of which, he conceives, is to give a greater surface by which it may be more firmly fixed to the substance against which the fly attaches it[178].

Besides these more striking variations in figure, their surface, though often smooth, is frequently curiously and most elegantly sculptured, a circumstance that distinguishes the eggs of no other oviparous animals. Some, as the margined egg just mentioned, are only sculptured on one side, the other being plain; or, as those of the Tusseh silk-worm[179] (Attacus Paphia) and other Bombyces, which have orbicular depressed eggs with a central cavity above and below, have their circumference crossed with wrinkles corresponding with the rings of the inclosed embryo[180]. Others again are sculptured all over. Of these, in some, the sculpture of the two sides is not symmetrical, as in those of a fly figured by Reaumur[181]: but in general there is a correspondence in this respect between the different parts of the egg. In those elegant ones before alluded to of some bird-louse attached to the golden pheasant, the shell resembles the purest wax, and is scored with longitudinal striæ, each distinguished by a series of impressed points, which give it a beautiful appearance of net-work. In the others, as in a common butterfly (Hipparchia Ægeria) and moth (Geometra cratægata), the whole surface is covered with hexagonal reticulations[182]. Others, as those of another butterfly[Pg 98] (Hipparchia Hyperanthus), are beset with minute granules or tubercles[183]. Others again, like those of the cabbage and hawthorn butterflies (Pieris Brassicæ and Cratægi), are remarkable for beautiful longitudinal ribs, often connected by elevated lines crossing them at right angles[184]; and in some, as in another butterfly (Hipparchia Jurtina), crowned by imbricated scales[185]. Many other minor differences in this respect might be noticed, but these will suffice to give some idea of the infinite variety exhibited in this respect by these little atoms. If the Creator has wrought them with so much art and skill, can it be beneath his reasonable creatures to examine and admire them, that they may glorify those attributes which they serve to illustrate?

Some eggs after exclusion occasionally become slightly corrugated: Malpighi supposed that this occurs only when the eggs are barren, having observed that those of the moth of the silk-worm which preserved their plumpness always produced caterpillars, while those which lost their original rotundity and became wrinkled were constantly unprolific. Bonnet, however, found exactly the reverse take place in another moth[186], so that these appearances are scarcely to be depended upon. Kuhn asserts, that a virgin female of the puss-moth (Cerura Vinula) having begun to lay eggs, which were yellow above, green below, and depressed, he introduced to her an hour afterwards a male, and some minutes subsequently to the union, she again deposited eggs, which were wholly of a dark brown and convex[187].

[Pg 99]

vii. Colour. The colour of the eggs of insects is as various as their shape and sculpture. They are very often white, those of some spiders like minute pearls[188]; some are yellow, as those of the silk-worm; others orange, such are the eggs of the bloody-nosed beetle (Timarcha tenebricosa); others again of a golden hue; sometimes they are of a sanguine red. I remember once being much surprised at seeing the water at one end of a canal in my garden as red as blood: upon examining it further I found it discoloured by an infinite number of minute red eggs, belonging probably to some dipterous insect of the Tipulidan tribe. There are also eggs of every intermediate shade between red and black; some again are blue and others green. They are not always of whole colours, for some are speckled like those of many birds, of which I can show you specimens, that are also shaped like birds' eggs; these I think were laid by a common moth (Odenesis potatoria); others are banded with different colours—thus the blue eggs of the lappet-moth (Gastropacha quercifolia) are encircled by three brown zones[189]; others are brown with a white zone[190].

Many eggs assume a very different colour after being laid a few days. In general upon their first exclusion they are white. Those of the chameleon-fly (Stratyomis Chamæleon) which I once found in great numbers, arranged like tiles on a roof one laid partly over another, on the under side of the leaves of the water-plantain, from white become green, and then change to olive green. Those of the hemipterous enemy of the larch, more than[Pg 100] once mentioned in this letter, are first mouse-coloured, then they assume a reddish hue, and lastly a blackish one. Those of the gnat from white in a short time assume a shade of green, in a few hours they are entirely green, and at length become gray[191]. Those of the silk-worm, which at first are of a yellow or sulphur colour, acquire a violet shade. The eggs of that rare moth Endromis versicolor, are at first sulphur-coloured, then green, next rose-coloured, and lastly blackish. The colour of almost all eggs changes when they are near hatching; but this change depends more frequently upon the colour of the included larva, which appears through the transparent shell of the egg, than upon any actual alteration in the egg itself.

viii. Period of hatching. The general rule for the hatching of the eggs of insects is the absorption by the embryo of all the superabundant moisture included in them; but the time varies according to the state of the atmosphere, to the action of which they are subjected. Like those of other animals, they require a certain degree of heat for the due evolution of the included larva. This heat in much the greater number of instances is derived from the temperature of the air, but often also from other sources. The eggs of the gad-fly tribe are hatched principally by the heat of the body of the animal to which they are committed; and doubtless the vital heat of various larvæ, small as it may be, must contribute something to the hatching of the eggs deposited in them by various Ichneumons. In the fermenting bark in which the instinct of the rhinoceros beetles (Oryctes nasicornis &c.)[Pg 101] impels them to place theirs, the dung which the Scarabæidæ select for that purpose, and the decaying vegetables chosen by many other insects, a degree of artificial heat must exist: and the eggs, or rather egg-like pupæ, of the spider-fly of the swallow (Ornithomyia Hirundinis) are hatched by the heat of those birds which sit upon them along with their own eggs.

Fabricius says, "Insects never sit upon their eggs[192];" but certainly, as I formerly related to you[193], the female earwig does this, and one would be induced to suppose, from the circumstance of the young ones following their mother, as chickens do the hen, that Pentatoma grisea (Cimex Linn.), formerly mentioned, may do the same[194].

With these exceptions, the eggs of all insects are hatched by atmospheric heat alone, the variations in which determine the more speedy or more tardy disclosure of the included insect. The eggs of such species as have several broods in the year, as the nettle butterfly (Vanessa Urticæ) when laid in summer are hatched in a few days; but if not laid till the close of autumn, they remain dormant through the winter, and are only hatched at the return of spring. That this difference is to be attributed to the influence of heat has been often proved by experiment: the autumnal eggs if brought into a warm room may be hatched as soon as those laid in the height of summer. Silk-worms' eggs naturally are not hatched till they have been laid six weeks, but in countries where they are reared, the women effect their exclusion in a much shorter period by carrying them in their bosoms: yet to retard their hatching with particular[Pg 102] views is in many circumstances impossible. When the heat of the atmosphere has reached a certain point, the hatching cannot be retarded by cellars; and M. Faujas has remarked, that in June the silk-worm's eggs would hatch in an ice-house[195].

The period of exclusion does not, however, depend solely upon temperature: the hardness or softness of the shell, and possibly differences in the consistence of the included fluid, intended to serve this very purpose, cause some eggs to be hatched much sooner than others exposed to the same degree of heat. Thus the eggs of many flesh-flies are hatched in twenty-four hours[196]; those of bees and some other insects in three days; those of a common lady-bird (Coccinella bipunctata) in five or six days; those of spiders in about three weeks; those of the mole-cricket in a month; while those of many Lepidoptera and Coleoptera require a longer period for exclusion. The hard eggs of Lasiocampa Neustria and castrensis, noticed above, remain full nine months before being hatched[197], as do those of another moth (Hypogymna dispar), which, though laid in the beginning of the warm month of August, do not send forth the included caterpillar till the April following[198]. We know no more of the cause of[Pg 103] this difference than of that which takes place in the period of exclusion of the eggs of the different species of birds.

Some eggs change considerably both their form and consistence previously to being hatched. M. P. Huber found that those of different species of ants when newly laid are cylindrical, opaque, and of a milky white; but just before hatching their extremities are arched, and they become transparent with only a single opaque whitish point, cloud, or zone, in their interior[199]. An analogous change takes place in the eggs of many spiders, which just before hatching exhibit a change of form corresponding with that which the included spider receives when its parts begin to be developed, the thin and flexible skin of the egg moulding itself to the body it incloses[200].

In proportion as the germe included in the egg is expanded, it becomes visible through the shell when transparent: this is particularly the case with spiders, in which, as was before observed, every part is very distinctly seen. At length, when all the parts are consolidated so as to be capable of motion, which in spiders takes place in four or five days after they begin to be visible in the egg, the animal breaks the pellicle by the swelling of its body and the movement of its legs, and then quits it, and disengages all its parts one after the other[201]. In general, at least where the shell is harder than that of spiders, insects make their way out by gnawing an opening with their mandibles in the part nearest their head, which, when the shell is very strong (as in Lasiocampa Neustria, &c.), it is often several[Pg 104] hours in accomplishing[202]. In many instances, however, the larva is spared this trouble, one end of the egg being furnished with a little lid or trap-door, which it has but to force up, and it can then emerge at pleasure: such lids are to be found in the eggs of several butterflies and moths, as Satyrus Mæra, Saturnia pavonia major, &c. and the common louse[203]. In those exquisitely elegant eggs, before described, of some kind of bird-louse (Nirmus) found adhering to the base of the neck feathers of the golden pheasant[204], there is a lid or cap of this kind of a hemispherical form terminating in a tortuous style. Those of a species of bug (Pentatoma Latr.), found by our friend the Rev. R. Sheppard, besides a convex lid are furnished with a very curious machine, as it should seem, for throwing it off. This machine is dark-brown, of a corneous substance, and of the shape of a cross-bow[205], the bow part being attached to the lid or pushing against it, and the handle, by means of a membrane, to the upper end of the side of the egg.

When the included animal has made its way out of the egg, it enters upon a new state of existence, that of Larva, to which I shall direct your attention in the following letter.

[Pg 105]

LETTER XXX.

STATES OF INSECTS.

LARVA STATE.

The Larva state is that in which insects exist immediately after their exclusion from the egg (or from the mother in ovo-viviparous species), in which they usually eat voraciously, change their skin several times, and have the power of locomotion, but do not propagate.

Almost all larvæ, at their birth, are for a time in a very feeble and languid state, the duration of which differs in different species. In most it continues for a very short time, a few minutes or perhaps hours, after which they revive and betake themselves to their appropriate food. In others, as in the generality of spiders, this debility lasts for seven or eight days, and in some species even a month, during which the young ones remain inactive in the egg-pouch[206], and it is not till they have cast their first skin that their active state of existence commences.

All larvæ may be divided into two great divisions:—

I. Those which in general form more or less resemble the perfect insect.

II. Those which are wholly unlike the perfect insect.

[Pg 106]

I shall begin by calling your attention to the characters of the first of these divisions: the second, which is by far the most numerous, will be afterwards considered.

I. The first division includes the larvæ of Scorpions, Spiders, Cockroaches, Grasshoppers, Lanthorn-flies, Bugs, &c.; or generally, with the exception of the Flea and Crustacea, the whole of the Linnean Orders Aptera and Hemiptera. All these larvæ, however remotely allied in other respects, agree in the general similarity which they bear to the perfect insects which proceed from them. The most acute entomologist, untaught by experience, could not even guess what would be the form of the perfect insects to be produced from larvæ of the second division, while they can recognise the form of the spider, the cricket, the cockroach, the bug, and the frog-hopper, in that of the larvæ. There are, however, differences in the degrees of this resemblance, according to which we may, perhaps, divide this tribe in their second state as follows:—

i. Those that resemble the perfect insect, except in the relative proportions and number of some of their parts.

ii. Those which resemble the perfect insect, except that they are apterous, or not yet furnished with organs of flight.

i. Spiders, Phalangia, scorpions, lice, Poduræ, sugar-lice (Lepisma), mites, centipedes, millepedes, &c. come under the first subdivision. The larvæ of the first six tribes here mentioned differ at their birth from the perfect insect, only in size and the proportions of their parts.[Pg 107] Thus the larvæ of spiders have their legs of a different relative length from that which they subsequently acquire; and the palpi in the males, which previously to the discoveries of Treviranus were regarded as their sexual organs, are not yet fully developed[207]: and a similar difference takes place in the legs of Phalangia. The general form too of the body undergoes slight alterations, and the colour very considerable ones, with each change of the skin—a change to which all these tribes are subject.

The larvæ of the three last-mentioned tribes (the mites, centipedes, and millepedes) differ from the perfect insect not only in the proportion but also in the number of their parts. Leeuwenhoeck states (and De Geer confirms his assertion, extending it to other species of mites[208]), that the common cheese-mite, which in its perfect state has eight legs, when first excluded from the egg has but six, the third pair being wanting[209]. Some however are born with eight legs, for instance A. eruditus of Schrank, which he saw come from the egg itself with that number[210]. Others again have never more than six legs: this is the case with Latreille's genera—Caris, Leptus, Atoma, and Ocypetes of Dr. Leach[211]. In the centipedes (Scolopendridæ) and millepedes (Iulidæ) differences still more remarkable, as I have stated in a former letter, have been observed by De Geer; these animals, in their progress to the perfect state, not only gain several additional pairs of legs, but also several additional segments of the body. This illustrious Entomologist found that Pollyxenus lagurus (Scolopendra L.) was born a hexapod,[Pg 108] with but three segments and as many pairs of feet, but successively acquired five additional segments with other appendages, and nine more pairs of feet[212]. A species of millepede (Iulus terrestris L.), which he also traced from its birth, and which begins the world at first with only eight segments and six feet, by a successive development at length acquires, in its perfect state, 50 segments and not less than 200 feet[213]. The nature of these very singular accretions, which Latreille and Mr. Wm. MacLeay have also observed in the centipedes[214], seems not well understood. If, as is most probable, though De Geer could not find any exuviæ[215], the larvæ cast a skin before each change, they do not essentially differ from the metamorphosis of other insects. The legs that these insects thus acquire are affixed to the abdomen, the six that they set out with being attached to the part representing the trunk, so that the former may be regarded as analogous to the prolegs of caterpillars. These animals therefore, as I have before intimated, invert the order of Nature, and from perfect degenerate into imperfect insects.

ii. If you examine the cockroach, cricket, or grasshopper, in different stages of their growth, you will find that the larva does not vary essentially from the perfect insect, except in wanting wings and elytra. The case is the same in almost all the Linnean genera of the modern order—Hemiptera; and with Raphidia, Termes, and Psocus, in the Neuroptera. Some of these, however, exhibit[Pg 109] slighter discrepancies in the proportion of some of their parts, but without affecting the general resemblance. Thus the larvæ of the common ear-wig have at first only eight, and subsequently nine joints to their antennæ, whereas the perfect insect has fourteen[216]; and the forceps is quite different, resembling rather two straight styles than what its name implies. In those also of many bugs (Coreus marginatus F. &c.), the joints of the antennæ are of a shape dissimilar to that which obtains in the perfect insect. In that of the common water-scorpion, the anal air-tube, which is so long in the imago, is scarcely visible[217]. In the Cicada tribe, so celebrated for their song[218], neither the larva nor the imago have the enormous thigh armed below with strong teeth, the tibiæ terminating in a fixed incurved claw, probably for the purpose of digging the holes into which they retire till they disclose the fly, which distinguish the pupæ of some species, and is particularly conspicuous in one commonly brought from China[219]. These often exhibit also other minor differences.

II. In treating of the second great division of larvæ, those that are wholly unlike the parent insect,—which includes, with few exceptions[220], the whole of the Linnean[Pg 110] orders, Coleoptera, Lepidoptera, Hymenoptera, Diptera, the majority of the Neuroptera, Coccus and Aleyrodes in Hemiptera, and the genus Pulex in Aptera,—I shall advert to their characters, under several distinct heads; and to avoid unnecessary circumlocution, I shall in what follows wholly leave out of consideration the first division already explained, and use the term larvæ with reference only to those of the second. The heads under which I propose to treat of them are: The substance of their body, its parts, shape, or figure, clothing, colour. Also the Economy or mode of life of these creatures: their food, moultings, growth, age, sex, and their preparations for assuming the Pupæ.

i. Substance, with the exception of the head and six fore-feet, which are usually corneous, the exterior integument or skin of larvæ is commonly of a membranous texture, and the body is of a much softer consistence than in the perfect insect. In those, however, of some Staphylinidæ and other Coleoptera, the dorsal part of the three first pieces, which represent the trunk of the perfect insect, is hard and horny. Some also have their whole skin coriaceous, as the tortoise-shell butterfly (Vanessa polychloros); and some few, as the wire-worm (Elater segetum), and other Elateres, very hard. I possess a very remarkable larva from Brazil, from the extreme flatness of its body, and from its having cavities to receive its legs when unemployed, probably living under bark, the skin of which is still harder than that of the grub of the Elaters. Perhaps it has to resist great pressure; and on that account is gifted with this quality, so seldom to be met with in other kinds of larvæ. The[Pg 111] interior of the body of these animals is generally of a softer consistence than in the perfect insect. Their intestines, and other internal organs, are usually wrapped in a voluminous substance of a fatty nature, which is regarded as analogous to the epiploon, omentum, or caul, which envelops the viscera of quadrupeds, &c., and is called by Reaumur the corps graisseux. The use of this general flexibility of larvæ is obvious; for, their bodies being mostly long and narrow, a hard rigid covering would have been very inconvenient, and a considerable impediment to their motions. When a caterpillar is feeding, it has occasion to apply its body to any part of the margin of a leaf so as to support itself by its prolegs, and when moving it wants to give it all the curves that are necessary to enable it to avoid obstacles, and thread its way through the sinuous labyrinths which it must often traverse. On the other hand, the hardness of the substance of its head affords a strong fulcrum to the muscles which keep its powerful jaws in constant play. The larvæ, indeed, of some Diptera have a membranous head; but their mandibles, which serve also as legs, are not grinders, but merely claws, the muscles of which require less powerful support[221]. Under this head it may be proper to observe, that generally larvæ are opaque; but some, as those of ants, and a few Lepidoptera[222], are diaphanous. That of Corethra crystallina (Tipula De Geer) is so beautifully transparent as to resemble[Pg 112] a piece of crystal, and scarcely to be distinguished from the water in which it lives[223].

ii. Parts. The body of each larva consists of the head, including its different organs, and of the succeeding segments, of which the three first may usually be denominated the trunk, and have the six anterior feet, when present, attached to their under side: the remainder is the abdomen. The latter includes in some species a variable number of membranous feet, as well as various appendages affixed usually to its tail and sides. No larva is ever furnished with wings[224]. Each of these greater divisions, and the organs which they include, require separate consideration.

1. Head. This, as was lately observed, is exteriorly of a horny substance, or at least harder than the rest of the body, in most larvæ; and on this account, though rarely separated from it by any visible distinct neck[225], is, if the[Pg 113] larva be of a tolerable size, distinguished at the first view. In those of many Dipterous insects, however, the head is covered with the same flexible membranous skin with the rest of the body, from which it is often scarcely to be distinguished. In these, except that it contains the organs of manducation, it wears no more the appearance of a head than any other segment of the body, and scarcely so much as the last or anal one. The head of these larvæ is also remarkable for another peculiarity,—that it is capable of being extended or contracted, and assuming different forms at the will of the insect: a property which the head of no superior animal can boast. It is probable that there is a considerable variety in the shape and circumstances of the heads of larvæ; but since, with the exception of those of Lepidoptera, they have had less attention paid to them than they deserve (indeed in a vast number of cases, from the difficulty of meeting with them, these variations, except in a few instances, have not been described), I will here mention a few of the most remarkable. The head of the young larva at its first exclusion from the egg is usually the most dilated part of the body, but it does not often continue so. In that of Cicindela campestris, however,—the beautiful green beetle sometimes found in sandy banks,—and also in several caterpillars of Lepidoptera, it is much larger than any of the following segments[226], which, in conjunction with the animal's formidable jaws, gives it a most ferocious appearance. In some lepidopterous larvæ the head is of the same diameter with the rest of the body, but in insects in general it may, I think, be stated as less; and[Pg 114] occasionally it bears no proportion whatever to it. This is the case with the subcortical one from Brazil lately mentioned. It is more commonly longer than broad; but in some, as in the larvæ of carrion beetles (Silphæ), the reverse of this takes place. Its shape varies from triangular to orbicular, the mouth of the animal forming the vertex of the triangle. In some larvæ of Hemerobii, however, the head is narrowest behind. That of the grub of a gnat noticed above (Corethra crystallina) forms a kind of sharp horn or claw, terminating the body anteriorly[227]. The contour of the head of larvæ is usually intire and unbroken; but in the caterpillars of some Lepidoptera, as the butterfly called the grand admiral (Vanessa Atalanta), the Glanville fritillary (Melitæa Cinxia), &c. it is divided into two lobes[228]. In the Brazil flat larvæ it is trilobed, each lateral lobe being divided into three smaller ones: in which circumstance it somewhat resembles the head of some subcortical Cimicidæ. Although the part we are treating of is generally without horns, yet in some tropical butterflies of the tribe of Nymphales, it is singularly armed with them. Thus Papilio Anchises is distinguished, according to Madame Merian[229], by two in the occiput, which it has the power of retracting. In the purple highflier (Apatura Iris), a British species, the[Pg 115] two lobes of the head, I am informed, terminate behind in two horns; as they do likewise in the brilliant Morpho Menelaus[230], the lobes assuming the form of a pear, and the horn representing the stalk. In a caterpillar I found amongst Mr. Francillon's larvæ, the head is bilobed, with a very long recurving subcapitate subramose spine. In Satyrus Cassiæ, the head is armed with three occipital stout spines[231]. The larva of Nymphalis Amphinome Latr. (Limenitis F.) is crowned with a coronet of eight occipital stout acute spines, the intermediate ones being the longest[232]; and that of Morpho Teucer has a similar coronet, consisting of only seven blunt rays, seemingly, rather than spines[233]. With regard to the articulation of the head with the trunk, it is generally by its whole diameter; but in some instances, only by a part of it. This is the case with one of a sphinx figured by Mad. Merian[234]; and I have another, probably belonging to the nocturnal Lepidoptera (Phalæna L.)[235]. In both these, the head is vertical and triangular; and in the latter (which is a remarkable creature, the tail itself being more like a head, and furnished with what resemble two prominent black eyes) the vertex of the triangle is considerably higher than the back of the animal. Whatever may be the clothing of the body, the head is usually naked. Sometimes, however, it is itself beset with very small simple spines, as in the butterfly of the mallow (Hesperia Malvæ); or with longer compound ones, such as are found on the rest of the body.[Pg 116] This is the case with one of a butterfly named by Rösel Papilio morsa. The most common colour of the head of larvæ, where it differs from the rest of the body, is a darker or lighter reddish brown, or piceous. This is particularly observable in those of Coleopterous insects, but it is very commonly in other tribes of the same hue. Sometimes, amongst the Lepidoptera, the head is of a different colour from the rest of the body; especially where a contrast renders it striking. I can show the caterpillar of some insect, probably of the hawk-moth tribe (Sphingidæ), from Georgia, remarkable for the length of its anal spine, in which the body is black, and the head red: another has a white head and a brown body. In the larvæ of some Lepidoptera, Coleoptera, and Diptera, the head can be wholly or nearly withdrawn within the first segment of the body. This may be readily seen in that of the common glow-worm; and that of a small gnat (Tipula replicata De Geer) withdraws it so completely that the anterior margin of that segment closes the orifice, so that the animal appears to have no head[236].—The parts of the head which require distinct consideration are, the eyes, antennæ, and the mouth: consisting of various organs, which will be specified. Some of these parts and organs are peculiar to larvæ of one order, others to those of another, and some are furnished with them all.

Eyes. The larvæ of many insects have no eyes. Those with antennæ which terminate in a lamellated clava (Scarabæus L.), and capricorn beetles also (Cerambyx L.),[Pg 117] amongst the Coleoptera, are without them, and probably several others; and amongst the Diptera, all those with a membranous or variable head. Those of the remaining orders, with the exception, perhaps, of some Hymenoptera and Lepidoptera, are furnished with these organs; and in the Coleoptera all the predaceous tribes, as well as most of those that are herbivorous or granivorous, and the Gnats and other Tipulidans (Tipulariæ Latr.) in the Diptera, are also distinguished by them. In the larvæ of the dragon-flies (Libellula L.), and other Neuroptera, they are composed of many facets as in those of the perfect insect, from which they differ chiefly in being smaller. But in the other insects of this description they are simple, and resemble those of the Arachnida, and many aptera. These simple eyes vary in their number, in different genera and tribes, from one to six on each side of the head. Thus the larva of Telephorus, and the saw-flies, has only one[237]; that of Cicindela three, the two posterior ones being large with a red pupil surrounded by a paler iris, which adds to the fierce aspect of this animal; and the anterior one very minute. Those of the tortoise-beetles also (Cassida) have three[238]; of Staphylinus, four; of Timarcha (the bloody-nosed beetle) five; of Carabus, and the Lepidoptera in general, six. In the last they are of different sizes, and generally arranged in a circle: in that of Hemerobius there are five in a circle, with one central one[239]. The appearance of these[Pg 118] globules, which are often not visible but under a powerful lens, is so different from that of the eyes of a butterfly or moth, or other perfect insect, that it has been doubted whether they actually perform the office of eyes, but without reason. They occupy the usual station of those organs, being situated in many instances upon a protuberance which appears to incase them; and seem of a construction closely analogous to that of the eyes of spiders, and the stemmata or ocelli of Hymenoptera, which have been satisfactorily proved to be organs of vision. In the larva of a moth not yet ascertained to exist in this country, Attacus Tau, and probably other species, the eyes, after the skin has been changed a few times, are no longer to be seen[240].

Antennæ. Most larvæ are provided with organs near the base of the mandibles, which from their situation and figure may be regarded as antennæ. Fabricius has asserted that the larvæ of the saw-flies (Tenthredo L.) have no antennæ; but in this he was mistaken, for though very short, they are discoverable in them, as he might have learned by consulting De Geer[241]. In the majority of Neuropterous larvæ, they almost precisely resemble those of the perfect insect. In all the rest they are very different. The antennæ of Coleopterous larvæ are usually either filiform or setaceous, consisting of four or five joints, nearly equal in length. Those of Lepidopterous larvæ are commonly conical, as are those likewise of Chrysomela and Coccinella &c. amongst the Coleoptera, and very short, composed of two or three joints, of which the last is much thinner than the first, and ends in one or[Pg 119] two hairs or bristles. These antennæ the larva has the power of protruding or retracting at pleasure. Lyonnet informs us, that the caterpillar of the great goat-moth (Cossus ligniperda) can draw the joints of its antennæ one within the other, so as nearly to conceal the whole[242]. The larva of the common gnat has two long incurved setaceous antennæ, fringed with hairs at some distance from their apex, which consist only of a single joint[243]. The greater number of Dipterous larvæ, however, all indeed except the Tipulidans (Tipulariæ Latr.), and many belonging to the Coleoptera and Hymenoptera orders (as those of Curculio, Apion, Apis, &c.), are wholly deprived of antennæ. It is a general rule, that the antennæ of larvæ are shorter than the same organs in the perfect insect, the tribe Ephemerina perhaps affording the only example in which the reverse of this takes place[244].

Mouth. All larvæ have a mouth situated in the head, by which they receive their food, and furnished with one or more instruments for the purpose of mastication and deglutition. These instruments, in all the orders except Lepidoptera, some Neuroptera and Diptera, bear a general resemblance to the same parts in the perfect insect. In larvæ of the Coleopterous, Lepidopterous, and Hymenopterous orders, we can distinguish for the most part an upper and under lip; two pairs of jaws answering to the mandibulæ and maxillæ; and two, four, or six palpi[245]: and some of these instruments may be found in most Diptera. Each of these parts require separate notice.

Upper-lip (Labrum). The mouth of almost all larvæ,[Pg 120] except some of the order Diptera, are provided with a distinct upper-lip, for retaining their food during mastication. As the construction of this part does not widely differ from that of the perfect insect, which will hereafter be more fully described, it is only necessary to observe, that it is usually a transverse moveable plate, attached posteriorly to the nasus (clypeus F.), and situated just above the mandibles[246].

Upper-jaws (Mandibulæ). The most usual figure of these, which are of a hard horny consistence[247], is that of two slightly concave, oblong, or triangular plates, often at their lower extremity of considerable thickness, and of very irregular form, the base of which is filled with powerful muscles, and planted in the side of the mouth so as to move transversely. The other extremity can be made to meet or diverge like the claws of pincers, and are divided into one or more tooth-like indentations, by means of which the food of the larva is cut[248]. This is their construction in the larvæ of all Lepidoptera, and in many of those of the other orders. They frequently, however, assume a different form, though their situation is always the same. Thus in the larvæ of the capricorn beetles (Cerambyx L.) and of other wood-boring species, they are shaped like the half of a cone, the inner sides of which, applying close to each other, form a pair of powerful grindstones, capable of comminuting the hardest[Pg 121] timber[249]. M. Cuvier has observed, with regard to the mandibulæ of those of stag-beetles (Lucanus), that besides their teeth at the extremity, they have towards their base a flat striated molary surface; so that they both cut and grind their ligneous food[250]. It seems to have escaped him, that a similar structure takes place in many perfect insects of the lamellicorn tribe, as I shall hereafter show you. In the larvæ of the water-beetles (Dytiscus L.), ant-lions (Myrmeleon L.), and lace-winged flies (Hemerobius L.), they resemble somewhat the forceps at the tail of an ear-wig, being long and incurved; and, what is more remarkable, hollow and perforated at the end, so as to serve as a channel for conveying into the larva's mouth the juices of the prey which by their aid it has seized. Reaumur even asserts, that the larva of Myrmeleon has no other entrance into its throat than through these tubular mandibles[251]. That of the rove-beetles (Staphylinus L.), and of many other Coleopterous genera, have these organs of this forcipate construction, without being perforated[252]. In the larva of the carnivorous flies, and many other Diptera, are two black incurved subulate parts, connected at the base, and capable of being protruded out of, and retracted into, the head, through the skin of which they are usually visible. As I informed you in a former letter[253], these mandibles are used for walking as well as feeding: they are parallel to each other, and are neither formed for cutting nor grinding[Pg 122] like the mandibles of other insects, but merely detach particles of food by digging into it and tearing the fibres asunder. In this operation they are probably assisted by an acutely triangular dart-like instrument of a horny substance, which in some species (Musca vomitoria) is placed between the two. In others this part is wanting. Some Dipterous larvæ have two similar mandibles, but instead of being parallel, they are placed one above the other; others (Musca domestica and meridiana) have but one such mandible, and some have no perceptible mandible of any kind. The mandibles of the larva of the crane-flies (Tipula), which are transverse and unguiform, do not act against each other, but against two other fixed, internally concave and externally convex, and dentated pieces[254].

Under-jaws (Maxillæ). These are a pair of organs, usually of a softer consistence, placed immediately under the upper-jaws; but as they are usually so formed and situated as not to have any action upon each other, it is probable that in general they rather assist in submitting the food to the action of the mandibulæ, than in the comminution of it. In Lepidopterous larvæ they appear to be conical or cylindrical (at least in that of the cossus so admirably figured by Lyonnet[255]), and to consist of two joints; which may, I imagine, be analogous to the upper and lower portions of which the maxillæ of perfect insects usually consist. The last of these joints is surmounted by two smaller jointed palpiform organs. If any part of the maxillæ can act upon each other, it is these organs or palpi; but it is evident they are not calculated for mastication, although they may assist in the retention of the[Pg 123] substance to be masticated. In a figure given by Reaumur of the under side of the head of another lepidopterous larva (Erminea Pomonella), the maxillæ consist of a single joint, and appear to be crowned by chelate palpi[256]: a circumstance which is also observable in that of a common species of stag-beetle (Lucanus parallelipipedus), the weevil of the water-hemlock (Lixus paraplecticus[257]), and other insects. In general the maxillæ of larvæ are without the lobe or lobes discoverable in those of most perfect insects, this part being usually represented by a kind of nipple, or palpiform jointed process, strictly analogous to the interior maxillary palpi of the predaceous coleoptera; but in most of the lamellicorn beetles the lobe exists in its proper form[258], as it does likewise in that of the capricorn-beetle before noticed (Callidium violaceum[259]). In the former instance, it is armed with spines or claws; but in the latter it is unarmed, and rounded at the end. In the larva of Cicindela campestris, the base of the maxilla runs in a transverse direction from the mentum, to which, as is usually the case, it is attached. From this at right angles proceeds the lobe, from the outer side of which the feeler emerges; and the inner part terminates in an unguiform joint, ending in two or three bristles. The structure in the larvæ of water-beetles (Dytiscus L.) is different, for they appear to be without maxillæ[260]; but the case really seems to be, that these organs are represented by the first joint of what M. Cuvier calls their palpi[261]; from which proceed the real palpi, the interior[Pg 124] one being very short, and consisting only of a single joint. These maxillæ of larvæ were regarded by Reaumur and other writers as parts of the under-lip, on each side of which they are situated; and indeed, as well as those in the perfect insect, they form a part of the same machine, being connected by their base with the mentum, which is part of the labium, but they are clearly analogous to the maxillæ of the imago. They are not to be found in the larvæ of many Dipterous insects, and perhaps in some species belonging to other orders. In some Neuropterous larvæ, as those of the Libellulina MacLeay, the maxillæ are of a substance quite as solid and horny as the mandibles, which in every respect they resemble[262].

Under-lip (Labium). Between the two maxillæ in the larvæ of most of the insects under consideration is a part termed by Reaumur the middle division of the under-lip, but which is in fact analogous to the whole of that organ in the imago. This organ varies in shape, being sometimes quadrangular, often conical, &c. Interiorly it is frequently connected with a more fleshy protuberance, called the tongue by Reaumur[263], and supplying the place of the ligula in the perfect insect. On each side of the apex of the under-lip is a minute feeler, and in the middle between these in the Lepidoptera and many others, is a filiform organ, which I shall call the spinneret (Fusulus), through which the larva draws the silken thread employed in fabricating its cocoon, preparatory to assuming the pupa state, and for other purposes[264]. This organ is[Pg 125] found only in those larvæ which have the power of spinning silk; that is, in all Lepidoptera, most Hymenoptera, Trichoptera, some Neuroptera, and even a Dipterous insect[265]. This tube, Lyonnet had reason to believe, is composed of longitudinal slips, alternately corneous and membranous, so as to give the insect the power of contracting its diameter, and thus making the thread thicker or smaller. There is only a single orifice at the end, which is cut obliquely, somewhat like a pen, only with less obliquity, and without a point, the opening being below, so as to be conveniently applicable to the bodies on which the larva is placed. Reaumur conceived that this spinneret had two orifices; but Lyonnet ascertained this to be a mistake, the two silk tubes uniting into one before they reach the orifice. From the contractile nature of the sides and the form of the orifice, combined with the power the insect has of moving it in every direction, results the great difference which we see in the breadth and form of the threads, some being seven or eight times as thick as others, some cylindrical, others flat, others channelled, and others of different thickness in different parts[266]. In the larvæ of many Diptera the under-lip is merely a small tubercle, which can be protruded from the insect's mouth by pressure[267].

One of the most remarkable prepensile instruments, in which the art and skill of a Divine Mechanician are singularly conspicuous, and which appears to be without a parallel in the insect world, may be seen in the under-lip of the various species of dragon-fly (Libellula L.). In[Pg 126] other larvæ this part is usually small and inconspicuous, and serves merely for retaining the food and assisting in its deglutition; but in these it is by far the largest organ of the mouth, which when closed it entirely conceals; and it not only retains but actually seizes the animal's prey, by means of a very singular pair of jaws with which it is furnished. Conceive your under-lip (to have recourse, as Reaumur on another occasion[268], to such comparison,) to be horny instead of fleshy, and to be elongated perpendicularly downwards[269], so as to wrap over your chin and extend to its bottom,—that this elongation is there expanded into a triangular convex plate[270], attached to it by a joint[271], so as to bend upwards again and fold over the face as high as the nose, concealing not only the chin and the first-mentioned elongation, but the mouth and part of the cheeks[272]: conceive, moreover, that to the end of this last-mentioned plate are fixed two other convex ones, so broad as to cover the whole nose and temples[273],—that these can open at pleasure, transversely like a pair of jaws, so as to expose the nose and mouth, and that their inner edges where they meet are cut into numerous sharp teeth or spines, or armed with one or more long and sharp claws[274]:—you will then have as accurate an idea as my powers of description can give, of the strange conformation of the under-lip in the larvæ of the tribes of Libellulina; which conceals the mouth and face precisely as I have supposed a similar construction of your lip would do yours. You will probably admit[Pg 127] that your own visage would present an appearance not very engaging while concealed by such a mask; but it would strike still more awe into the spectators, were they to see you first open the two upper jaw-like plates, which would project from each temple like the blinders of a horse; and next, having by means of the joint at your chin let down the whole apparatus and uncovered your face, employ them in seizing any food that presented itself, and conveying it to your mouth. Yet this procedure is that adopted by the larvæ provided with this strange organ. While it is at rest, it applies close to and covers the face. When the insects would make use of it, they unfold it like an arm, catch the prey at which they aim by means of the mandibuliform plates, and then partly refold it so as to hold the prey to the mouth in a convenient position for the operation of the two pairs of jaws with which they are provided. Reaumur once found one of them thus holding and devouring a large tadpole;—a sufficient proof that Swammerdam was greatly deceived in imagining earth to be the food of animals so tremendously armed and fitted for carnivorous purposes. Such an under-lip as I have described is found in the tribe of dragon-flies (Libellulina); varied, however, considerably in its figure in the different genera. In the larva of Libellula Fab., such as Libellula depressa, &c. it is of the shape above described; so exactly resembling a mask, that if Entomologists ever went to masquerades, they could not more effectually relieve the insipidity of such amusements and attract the attention of the demoiselles, than by appearing at the supper table with a mask of this construction, and serving themselves by its assistance. It would be difficult, to be sure, by mechanism to supply the place of the muscles[Pg 128] with which in the insect it is amply provided: but Merlin, or his successor, has surmounted greater obstacles. In the larva of the Fabrician Æshnæ (Libellula grandis, &c. L.), this apparatus is not convex but flat: so that, though it equally conceals the face, it does not so accurately resemble a mask; and the jaws at its apex are not convex plates, but rather two single conical teeth[275]. It is, as to its general shape, similarly constructed in Agrion Fab. (L. Virgo, &c. L.); but the first joint is more remarkably elongated, the jaws more precisely resemble jaws than in any of the rest, and are armed with three long, very sharp teeth: between them also there is a lozenge-shaped opening, through which, when the apparatus is closed, is protruded a circular sort of nipple, apparently analogous to the ligula[276]. Libellula ænea, L., which is the type of another tribe (Cordulia Leach), has a mask somewhat different from all the above, the jaws being armed with a moveable claw and an internal tooth[277]. You will admire the wisdom of this admirable contrivance, when you reflect that these larvæ are not fitted to pursue their prey with rapidity, like most predaceous animals; but that they steal upon them, as De Geer observes[278], as a cat does upon a bird, very slowly, and as if they counted their steps; and then, by a sudden evolution of this machine, take them as it were by surprise, when they think themselves safe. De Geer says, it is very difficult for other insects to elude their attacks, and that he has even seen them devour very small fishes[279].[Pg 129] As these animals are found in almost every ditch, you will doubtless lose no time in examining for yourself an instance of so singular a construction.

Feelers (Palpi). In the orders Diptera and Hymenoptera are many larvæ in which these organs have not been certainly discovered; yet Reaumur in that of a common fly (M. meridiana L.) found four retractile nipples[280] which seem analogous to them; and Latreille has observed, that below the mandibles of those of ants are four minute points, two on each side[281]: but in all other larvæ their existence is more clearly ascertained. The maxillary palpi vary in number, many having two on each maxilla and others only one. In the perfect insect the former is one of the distinguishing characters of the predaceous beetles (Entomophagi Latr.), but in the larvæ it is more widely extended; since even in the caterpillars of Lepidoptera the inner lobe of the maxilla which represents this feeler is jointed, which is precisely the case with the beetles just named. Cuvier has observed this circumstance in the larva of the stag-beetle[282]; and it belongs to many other Coleoptera that have only a pair of maxillary palpi in the perfect state. The labial palpi are always two, emerging usually one on each side from the apex of the under-lip. With regard to the form of the palpi, those of the Lepidoptera are mostly conical; in other orders they are sometimes setaceous and sometimes filiform. Their termination is generally simple, but sometimes the last joint is divided. They are for the most part very short, and the labial shorter than the[Pg 130] maxillary. The latter never exceed four joints[283], which seems the most natural number; and the former are limited to three. Both vary between these numbers, and one joint. The joints, though commonly simple, are sometimes branched. This is the case with one I met with in considerable numbers upon the Turnip, in October 1808, the second joint of the palpi of which sends forth near the apex an internal branch. In the larva of the Cossus, as Lyonnet informs us[284], the joints of the palpi are retractile, so that the whole of the organ may be nearly withdrawn.

After thus describing the head of larvæ, and its principal organs, we must next say something upon the remainder of the body, or what constitutes the

2. Trunk and Abdomen: which I shall consider under one article. These are composed of several segments or rings, to which the feet and other appendages of the body are fixed. The form of these segments, or that of their vertical section, varies considerably: in many Lepidoptera, the wire-worm, &c., it would be nearly circular; in others a greater or less segment of a circle would represent it; and in some, perhaps, it would consist of two such segments applied together. Their lower surface is generally nearly plane. Their most natural number, without the head and including the anal segment, is twelve: this they seldom exceed, and perhaps never fourteen. The three first segments are those which represent[Pg 131] the trunk of the perfect insect, and to which the six anterior legs when present are affixed. In general, they differ from the remaining segments only in being shorter, and in many cases less distinctly characterized; but in Neuropterous larvæ, those of Dytisci, and some other Coleoptera, they are longer than the succeeding ones, and pretty nearly resemble the trunk of the animal in its last state. The surface of the trunk and abdomen will be considered under a subsequent head; I shall not, therefore, describe it here. The conformation of the different segments varies but little, except of the terminal one, or tail, which in different larvæ takes various figures. In most, this part is obtuse and rounded; in others acute or acuminate; in others truncate; and in others emarginate, or with a wider sinus, and with intermediate modifications of shape which it would be endless to particularize. In some, also, it is simple and unarmed; in others beset with horns, spines, radii, and tubercles of different forms, some of which will come under future consideration. The parts connected with the trunk and abdomen which will require separate consideration, are the legs, the spiracles, and various appendages.

Legs. It may be stated generally that the larvæ of the orders Coleoptera, Lepidoptera, and Neuroptera, have legs; and that those of the orders Hymenoptera and Diptera have none. This must be understood, however, with some exceptions. Thus the larvæ of some Coleoptera, as the weevil tribes (Curculio L.) have no legs, unless we may call by that name certain fleshy tubercles besmeared with gluten, which assist them in their motions[285];[Pg 132] while those of Tenthredo and Sirex in the order Hymenoptera are furnished with these organs. At present I know no Dipterous larva that may be said to have real legs, unless we are to regard as such certain tentacula formed upon a different model from the legs of other larvæ[286]. Rösel has, I think, figured a Lepidopterous apode. No Neuropterous one has yet been discovered.

The legs of larvæ are of two kinds; either horny and composed of joints, or fleshy and without joints[287]. The first of these, as I observed in a former letter[288], are the principal instruments of locomotion, and the last are to be regarded chiefly as props and stays by which the animal keeps its long body from trailing, or by which it takes hold of surfaces; while the other legs, or where there are none, the annuli of its body, regulate its motions. The former have been commonly called true legs (pedes veri), because they are persistent, being found in the perfect insect as well as in the larva; and the latter spurious legs (pedes spurii), because they are caducous, being found in the larva only. Instead of these not very appropriate names, I shall employ for the former the simple term legs, and for the latter prolegs (propedes)[289].

The legs, when present, are always in number six, and attached by pairs to the underside of the three first segments of the trunk. They are of a horny substance, and consist usually of the same parts as those of the perfect[Pg 133] insect; namely, coxa, trochanter, femur, tibia, and tarsus, suspended to each other by membranous ligaments: these parts are less distinctly marked in some than in others. Thus in the legs of a caterpillar, or the grub of a capricorn-beetle, at first you would think there were only three or four joints besides the claw; but upon a nearer inspection, you would discover at the base of the leg the rudiments of two others[290], in the latter represented indeed by the fleshy protuberance from which the legs emerge. In the larvæ of the predaceous Coleoptera, the hip and trochanter are as conspicuous nearly as in the perfect insect; and the tarsus, which still consists of only a single joint, is armed with two claws[291]. In those of the Neuroptera order, in which all the joints are very conspicuous, the tarsi are jointed, as well as two-clawed[292]. The legs of larvæ are usually shorter than those of the perfect insect, and scarcely differ from each other in shape, for they all gradually decrease in diameter from the base to the apex. This is the most usual conformation of them in Lepidopterous, Hymenopterous, and some Coleopterous larvæ, (those of the capricorn-beetles are very short and minute, so as to be scarcely visible,) in which they are so small as to be concealed by the body of the insect[293]. In Neuropterous larvæ, however, and[Pg 134] several Coleoptera, as those of Dytiscus, Staphylinus, Coccinella, &c., they more resemble the legs of the perfect insect, the joints being more elongated, and the femoral one projecting beyond the body[294].

You will find no other than true legs in most Coleopterous, Neuropterous, and Hymenopterous larvæ. But those of the saw-flies (Tenthredo L.), and all caterpillars, have besides a number of prolegs: a few Dipterous larvæ also, are provided with some organs nearly analogous to them. These prolegs are fleshy, commonly conical or cylindrical, and sometimes retractile protuberances, usually attached by pairs to the underside of that part of the body that represents the abdomen of the future fly[295]. They vary in conformation and in number; some having but one, others as many as eighteen.

With regard to their conformation, they may be divided into two principal sections: first, those furnished with terminal claws; and secondly, those deprived of them. Each of which may be divided into smaller sections, founded on the general figure of the prolegs, and arrangement of the claws or hooks.

[Pg 135]

i. The prolegs of almost all Lepidopterous larvæ are furnished with a set of minute slender horny hooks, crotchets, or claws, of different lengths, somewhat resembling fish-hooks; which either partially or wholly surround the apex like a pallisade. By means of these claws, of which there are from forty to sixty in each proleg, a short and a long one arranged alternately, the insect is enabled to cling to smooth surfaces, to grasp the smallest twigs to which the legs could not possibly adhere: a circumstance which the flexible nature of the prolegs greatly facilitates[296]. Claws nearly similar are found on the prolegs of some Dipterous larvæ[297], but not in any of those of the other orders. These last, however, are seldom either so numerous, or arranged in the same manner, as in caterpillars. When the sole of the foot is open, the claws with which it is more or less surrounded are turned outwards, and are in a situation to lay hold of any surface; but when the animal wishes to let go its hold, it begins to draw in the skin of the sole,[Pg 136] and in proportion as this is retracted, the claws turn their points inwards, so as not to impede its motion[298].

The prolegs with claws may be further divided into four different kinds.

1. In the larvæ of the great majority of butterflies and moths they assume the form of a truncated cone, the lower and smaller end of which is expanded into a semicircular or subtriangular plate, having the inner half of its circumference beset with the claws above mentioned; and, from its great power of dilating and contracting, admirably adapted for performing the offices of a foot. Jungius calls these legs pedes elephantini[299]; and the term is not altogether inapplicable, since they exhibit considerable resemblance to the clumsy but accommodating leg and foot of the gigantic animal he alludes to.

2. The larvæ of many minute moths, particularly of the Fabrician genera Tortrix and Tinea—those which live in convoluted leaves, the interior of fruits, &c., as well as the Cossus, and some other large moths,—have their prolegs of a form not very unlike those of the preceding class, but shorter, and without any terminal expansion; the apex, moreover, is wholly, instead of half, surrounded with claws[300]; the additional provision of which, together with a centrical kind of nipple capable of being protruded or retracted, in some measure, though imperfectly, supplies the place of the more flexible plate-like expansion present in the first class.

3. The third class is composed of a very few Lepidopterous larvæ which have their prolegs very thick and conical at the base, but afterwards remarkably slender,[Pg 137] long, and cylindrical, so as exactly to assume the shape of a wooden leg[301]. These, as in the first class, are expanded at the end into a flat plate: but this is wholly circular, is surrounded with claws, and has also in the middle a retractile nipple, as in the preceding class. In Cossus, at least in an American species (Cossus Robiniæ), described by Professor Peck[302], the anal prolegs have the claws only on their exterior half.

4. The remaining description of unguiferous prolegs, if they may not rather be deemed a kind of tentacula, are those of certain Diptera, provided with no true legs; which differ from the three preceding classes, either in their shape, or the arrangement of their claws. In one kind of those remarkable larvæ, which from their long respiratory anal tubes Reaumur denominates "rat-tailed," that of Elophilus pendulus, there are fourteen of these prolegs, affixed by pairs to the ventral segments, the twelve posterior ones of which are subconical, and truncate at the apex, which is surrounded with two circles of very minute claws, those of the inner being much more numerous and shorter than those of the exterior circle; while the anterior pair terminate in a flat expansion, and in shape almost exactly resemble those of a mole[303]. The prolegs of the larvæ of a kind of gnat called by De Geer Tipula amphibia, and of Syrphus mystaceus F., (Musca plumata De Geer,) are nearly of a similar construction, but in the last are armed with three claws only[304]. Long moveable claws also distinguish the singular[Pg 138] prolegs before described[305] of another gnat (Tanypus maculatus Meig., Tipula De Geer). The case-worms (Trichoptera K.) and some others, have two prolegs at the anus, each furnished with a single claw[306].

ii. The prolegs deprived of claws are found in the larva of the Hymenopterous tribe of saw-flies (Tenthredo L.), in those of some Lepidoptera (Hepialus F. &c.), and in some few Coleopterous and Dipterous genera. Those of the former are of the shape of a truncated cone, and resemble the second class of unguiculate prolegs, except in the defect of claws. In the latter they are a mere retractile nipple-like protuberance, in some species so small as scarcely to be perceptible. In all they aid in progressive motion; but it is by laying hold of surfaces, and so enabling the body more readily to push itself forward by annular contraction and dilatation, and not by taking steps, of which all prolegs are incapable: to assist in this purpose the protuberance sometimes secretes a gluten[307], which supplies the place of claws. Some larvæ have the power of voluntarily dilating certain portions of the underside of their body, so as to assume nearly the shape and to perform the functions of prolegs. In a Coleopterous (?) subcortical one from Brazil, before alluded to, there are four round and nearly flat areas in each ventral segment of the abdomen, but the last very little raised above the surface, and rough, somewhat like a file; and besides these, the base of the anal segment has ten of these little rough spaces, but of a different shape, being nearly linear, placed in a double series, five on each side. Doubtless these may be regarded as a kind of prolegs,[Pg 139] which enable the animal to push itself along between the bark and the wood[308].

In considering, in the next place, the number and situation of the prolegs, it will contribute to distinctness to advert to these circumstances as they occur in the different orders furnished with these organs.

To begin with the Lepidoptera.—Lepidopterous larvæ have either ten, eight, six, or two prolegs, seldom more[309], and never fewer. Of these, with a very few exceptions, two are attached to the last or anal, and the rest, when present, to one or more of the sixth, seventh, eighth, and ninth segments of the body: none are ever found on the fourth, fifth, tenth, or eleventh segments.

1. Where ten prolegs are present, as is the case in by far the greatest proportion of Lepidopterous larvæ, there is constantly an anal pair, and a pair on each of the four intermediate segments just mentioned.

2. In caterpillars, which like those of a few species of the genera Sphinx, Pyralis, and of the Bombycidæ, &c. have eight legs, they are placed in three different ways. In those which have an anal pair, the remaining six are in some fixed to the sixth, seventh, and eighth; in others, to the seventh, eighth, and ninth segments. In those which, like Cerura Vinula, and several other species of the same family, have no anal prolegs; the whole eight emerge from the sixth, seventh, eighth, and ninth segments.

3. The Hemigeometers, as Noctua Gamma, &c. have[Pg 140] only six legs: namely, an anal pair, and two ventral ones, situated on the eighth and ninth segments.

4. The larvæ of the Geometers (Geometræ F.) have but four prolegs; of which two are anal, and two spring from the ninth segment. It should be observed, however, that the larvæ of Hemigeometers, and even of some of those that have ten prolegs, where the four anterior ones are much shorter than the rest, move in the same way as the Geometers. This even prevails in a few where these organs are all of equal length.

5. Many of the larvæ of Tinea L. which live in the interior of fruits, seeds, &c., have but one pair of prolegs, which are attached to the anal segment.

6. The larvæ of Haworth's genus Apoda (Hepialus Testudo and Asellus F.), remarkable for their slug-like shape and appearance, move by the aid of two lateral longitudinal pustule-like protuberances, which leave a trace of a gummy slime in their course.

Hymenoptera.—The larvæ of the different tribes of Tenthredo L., almost the only Hymenopterous insects in which prolegs are present, have a variable number of these organs; some sixteen, as the saw-fly of the willow (T. lutea L.), and this is the most numerous tribe of them, including the modern genera, Cimbex F., Pterophorus, &c. Others have fourteen, as that of the cherry (T. cerasi L.); and many others with only nine joints to their antennæ. A third class have only twelve, as that of the rose (T. Rosæ L.), but this contains but few species. The last class contains those that have no prolegs at all, but only the six horny ones appended to the trunk. Of this tribe, the caterpillars of which have a very different aspect from the preceding, are those of the genus Lyda F. (T. crythrocephala[Pg 141] L.)[310]. Two of the prolegs are anal, and the rest intermediate, and none are furnished with claws. This circumstance, in conjunction with the greater number of prolegs, except in the case of Lyda, will always serve as a mark to distinguish these fausses chenilles, as the French call the larvæ of saw-flies, from true caterpillars. The dorsal prolegs of a species of Cynips described by Reaumur have been before noticed.

Coleoptera.—The larvæ of insects of this order are so little known or attended to, that no very accurate generalization of them in this respect is practicable. Many of them, in addition to their six horny legs, have a proleg at the anus; which in many cases appears to be the last segment of the abdomen, forming an obtuse angle with the remainder of it, so as to support that part of the body, and prevent it from trailing; and in some instances, as in Chrysomela Populi, a common beetle, secreting a slimy matter to fix itself[311]. In the larvæ of Staphylinidæ this proleg is very long and cylindrical; in that of Cicindela it is shorter, and in shape a truncated cone rather compressed; it is very short, also, in those of the Silphæ that I have seen. In the wire-worm (Elater Segetum) it is a minute retractile tubercle, placed in a nearly semicircular space, shut in by the last dorsal segment, which becomes also ventral at the anus. This space is in fact[Pg 142] the last ventral segment. This seems characteristic of the genus[312]. From the underside of the body of the common meal-worm (Tenebrio Molitor), at the junction of the two last segments, when the animal walks, there issues a fleshy part, furnished below with two rather hard, long, and moveable pediform pieces, which the animal uses in walking[313]. In the larva of another beetle, whose ravages have been before noticed, under the name of the cadelle[314] (Trogosita mauritanica), a pair of prolegs are said to be found under the anal segment; and in that of the bloody-nose beetle (Timarcha tenebricosa), that segment is bifid. That of the weevil of the common water-hemlock (Lixus paraplecticus F.) exhibits a singular anomaly: prolegs occupy the usual station of the true legs, being attached to the three segments representing the trunk[315]. This insect, however, does not appear to use them in moving. A pair in each of the twelve segments of the body are found in the grub of another weevil (Hypera Rumicis Germ.), the nine last pair being the shortest, which all assist the insect in walking[316]. But the greatest number of prolegs is to be found in the Brazil subcortical larva lately mentioned. Besides the six horny legs of the trunk, this remarkable animal has four prolegs on each of the seven intermediate abdominal segments, and five on each side of the base of the last, making the whole number of prolegs, if so they may be called, amount to forty-four: a far greater number than is to be found in any larva at present known. When I wrote to you upon the motions of insects, I informed[Pg 143] you that some larvæ moved by means of legs upon their back[317], but I was not then aware that any were furnished with them both on the back and the belly at the same time. By the kindness of Mr. Joseph Sparshall of Norwich, a very ardent and indefatigable entomologist, I am in possession of the larva of Rhagium fasciatum, a timber-feeding beetle. This animal on the ten intermediate segments of the underside of the body, which in the centre form a fleshy protuberance, has on it a double series of rasps, as it were, consisting each of two rows of oblique oblong prominences; and on the seven intermediate dorsal segments there are also in the centre seven rasps of three or four rows each, of similar prominences: so that this animal at the same time can push itself along both by dorsal and ventral prolegs. It is worthy of observation, that a pair of these rasps is between the second and third pair of true legs.

Diptera.—The larva of a little gnat, Tipula stercoraria De Geer[318] (Chironomus Meig.?), drags itself along by the assistance of a single tubercle, placed on the underside of the first segment of the body, which the animal has the power of lengthening or contracting[319]. That of another beautiful Chironomus (C. plumosus), remarkable for the feathered antennæ of the male[320], has two short prolegs, or pediform but not retractile tentacula in the same situation[321]. Others, as that of Tanypus maculatus,[Pg 144] &c. have two pairs, one attached to the anal and the other to the first segment[322]. Tipula amphibia De Geer in this state has ten prolegs, placed by pairs on the fourth, fifth, eighth, ninth, and tenth dorsal segments[323]; and Scæva Pyrastri F., one of the aphidivorous flies, has not fewer than forty-two, arranged in a sextuple series, seven in each row[324].

It may not be useless to close this long description of the legs of larvæ with a tabular view of them, founded chiefly upon these organs; which afford very obvious marks of distinction.

1. Larvæ without legs.
   1. With a corneous head of determinate shape (coleopterous and hymenopterous apods—Culicidæ, some Tipulidæ, &c. amongst the Diptera).
   2. With a membranaceous head of indeterminate shape (Muscidæ, Syrphidæ, and other Diptera).
2. Larvæ with legs.
   1. With legs only, and with or without an anal proleg (Neuroptera, and many Coleoptera).
      1. Joints short and conical (Elater, Cerambycidæ, &c.).
      2. Joints long and subfiliform (Staphylinus, Coccinella, Cicindela, &c.).
   2. Prolegs only (many Tipulidæ, and some subcutaneous Lepidopterous larvæ, &c.).
   3. Both legs and prolegs (Lepidoptera, Tenthredinidæ, and some Coleoptera).
      1. Without claws (Tenthredinidæ, &c.).
      2. With claws (Lepidoptera, &c.).

[Pg 145]

I should next say something upon the spiracles, or breathing-pores, or any other external apparatus for the purpose of respiration, in larvæ; but I think it will be best to reserve the consideration of these for a subsequent Letter. We will therefore conclude this detailed description of their parts in their first state, with some account of their other.

iii. Appendages. The generality of larvæ have no other external organs than those already described; but in several of them we observe various kinds of retractile ones and others—protuberances—horn-like processes—rays, &c.; which, though not properly coming either under any of the above parts, or under the clothing of these animals, yet require to be noticed. Upon these I shall now enlarge a little.

You must have observed upon the back of the last segment but one of the caterpillar of the silk-worm a horn-like process, rising at first nearly perpendicularly, and then bending forward. A similar horn, though confined in the genus Bombyx to the silk-worm and a few others, if we may believe Madame Merian, who, however, often makes great mistakes, is found in the beautiful caterpillar of one of the largest and finest moths that we know (Erebus Strix[325]), the glory of the Noctuidæ, and in most of those of the hawk-moths (Sphinx F.) [S. Porcellus, Vitis, and a few others excepted; in some of which, as S. Labruscæ, &c., this anal horn is replaced by a gibbosity, and in others, as S. Œnotheræ, by a callous eye-like plate[326]] in the same situation, but much longer[327], and[Pg 146] commonly curving backwards over the tail[328]. Sometimes, however, as in S. ocellata and S. Stellatarum, it is perfectly straight. These organs towards the apex are horny, and often end in a sharp point; nearer the base they are fleshy. They are without any true joint[329], yet the insect can elevate or depress them at pleasure. Under a lens, they usually appear covered with spinous eminences, arranged like scales. The use of these horns is quite unknown: Goedart fancies that they secrete a potent poison, and are intended as instruments of defence; but both suppositions are altogether unfounded. It has been remarked, that the body of those caterpillars which have these horns, is firmer, and yields less to the touch than that of those which have no such appendages[330]. The larva of a small timber-devouring beetle (Lymexylon dermestoides F.) has, like the above caterpillars, a long horn, and in the same situation: it has also a singular protuberance on the first segment[331]. Upon some other caterpillars, as in Bombyx Stigma F., a singular pair of horn-like appendages arises from the back of the second segment of the body, excluding the head. In a tawny-coloured one from Georgia, with a transverse row of short black spines on each segment, these horns are half an inch long, black, covered with spinous eminences, rather thickest at the base, and terminate in a little knob. They appear to articulate with the body at the lower extremity. I have another species, black, with narrow longitudinal yellow[Pg 147] stripes, in which these horns are of equal thickness at base and apex, but with the same terminal knob. Danais Archippus has a pair of tentacula at the head, and another pair, but shorter, at the tail; and D. Gylippus has, besides these, two in the middle of the body[332].

We are equally ignorant of the use of the upright horn found upon the back of the fourth segment in the larva of some moths (Noctua Psi, and tridens F.) which is of a construction quite different from that of those last described. It is cylindrical, slightly thinner at the apex, which is obtuse, fleshy, incapable of motion, of a black colour, and about two lines long. On the same segment, also, in the case-worms (Trichoptera K.) are three fleshy conical eminences, which the animal can inflate or depress, so that they sometimes totally disappear, and then in an instant swell out again. When retracted, they form a tunnel-shaped cavity, varying in depth[333]. Reaumur conjectured that these eminences were connected with respiration, and one circumstance seems in favour of this conjecture, that this segment has not the respiratory threads observable in the subsequent ones. Latreille mentions certain fleshy naked eminences placed upon the ninth and tenth segments of some hairy caterpillars, which, like those just mentioned, the animal can elevate more or less. They are often little cones; but when it would shorten them, the summit is drawn in, and a tunnel appears where before there was a pyramid[334].

In a former Letter I gave you a short account of the[Pg 148] remarkable Y-shaped, as it should seem, scent-organs (Osmateria) of the beautiful caterpillar of the swallow-tailed butterfly (Papilio Machaon L.), and others of the Equites[335]; I will now speak of them more fully. That found in the former is situated at the anterior margin at the back of the first segment, close to the head, from which at first view it seems to proceed. At the bottom it is simple, but divides towards the middle, like the letter Y, into two forks, of a fleshy substance[336], which it can lengthen, as a snail does its horns, to five times their ordinary extent, or retract them within the stalk, so as wholly to conceal them. Sometimes it protrudes one fork, keeping the other retracted; and often withdraws the whole apparatus for hours together under the skin, and its place is only marked by two tawny-coloured dots, so that an ordinary spectator would not suspect the existence of such an instrument[337]. Unfortunately this larva is rare in this country, so that I can scarcely flatter you with the hope of seeing this curious organ in a living specimen[338], unless you choose to import a parcel of its eggs from the south of Europe, where it is common. This you will think rather a wild proposition; but why should not Entomologists import the eggs of rare insects, as well as botanists the seeds of rare plants? But if you will be satisfied with the dissection of a dead specimen, I have several,[Pg 149] done by the ingenious Mr. Abbott of Georgia, in which this part is well exhibited[339].

Another small caterpillar, as it should seem, of a geometer, prepared by the same gentleman, exhibits a pair of similar horns on the fifth and sixth segments: in these the common base from which the fork proceeds is very short and wide, and each branch grows gradually more slender from the base to the apex, where it is involute. Whether these are retractile, or whether they correspond with those of P. Machaon in their nature and use, cannot be ascertained from a dead specimen: as they belong to a larva of a quite different tribe of Lepidoptera, the probability is, that they essentially differ. Two globose retractile vesicles issue from the ninth and tenth segments of those of Arctia chrysorrhea, &c.[340]

A great number of Lepidopterous larvæ, particularly those which are smooth and of a moderate size, have between the under-lip and fore-legs a slender transverse opening, containing a teat-like protuberance of the same construction as the furcate horn of the caterpillar of the beautiful mountain-butterfly, Parnassius Apollo; and, like that, can either be wholly retracted and concealed, or by pressure be extended to the length of one of the legs. In some larvæ this part is of a subhemispherical figure, generally single, but sometimes double. It is commonly, however, more slender and conical; and when of this shape, it is sometimes quadruple[341]. The use of this part is not very clearly known: some have supposed it to be a second spinneret, and to be of use in fabricating the cocoon; but[Pg 150] it is more probable that it secretes some other kind of fluid, and is connected with defence.

The singular organ in a similar situation, evidently for that purpose, with which the puss-moth endeavours to annoy its assailants, has been described in a former Letter, to which I refer you[342]. Bonnet, who was the first that discovered this organ, ascertained that it might be cut off without injury to either larva or imago. He also remarked in a caterpillar found in the wild succory (Cichorium Intybus) another short, black, needle-shaped organ between the conical part just described and the under-lip[343]. De Geer mentions a remarkable fleshy horn-like style, which issues from the lower side of the first segment, between the head and the legs of the case-worms (Trichoptera): he does not describe it as retractile, or it might be regarded as analogous to those of Lepidoptera similarly situated, that I have just noticed[344]. In that of the emperor-moth (Saturnia Pavonia), there are perforated tubercles, which when the animal is molested spirt forth a transparent fluid[345].

The horn-like appendage of the puss-moth (Cerura Vinula) is situated at the tail of the insect, and is composed of two distinct cylindrical diverging branches, each about four lines long, not united at the base. Each of these is hollow, and includes a smaller cylindrical piece, which can be protruded at pleasure, and withdrawn again, as a pencil within its case; or, rather, as the horns of a snail. The two outer horns are tolerably firm, moveable at their base, and beset with black spines; the interior tentacula are fleshy, moveable in every direction, and in full-grown[Pg 151] larvæ of a rose colour. The animal seldom protrudes them, unless in some way disturbed; and frequently it approximates the two outer cases so closely that they resemble a single horn. It appears to use these inner horns, when protruded, as a kind of whip to drive away the flies, especially the Ichneumons, that alight upon its body. When touched in any place, it will unsheath one of them, and sometimes both, and with them strike the place where it is incommoded[346]. A similar organ is found in some other Bombycidæ, as B. Tau and Furcula F. Reaumur mentions a caterpillar that to this kind of tail added the resemblance of two ears, or two cylindrical bodies, terminating in a point, which emerged from the first segment behind the head[347]. In another observed by the same author, the legs were replaced by a single horn, but which did not appear to send forth an internal one: from the back of its fourth segment also emerged a single conical or pyramidal fleshy eminence or cleft, terminating in two points[348]. Some of the tropical butterflies also, as may be seen in the figures of Madame Merian, have two diverging anal horns instead of anal prolegs; but it does not appear that they incase tentacula[349]. Wherever these caudal horns are found, the above prolegs are wanting[350].[Pg 152] Two conical anal horns also distinguish the caterpillar of one of the moths called Prominents, Notodonta camelina; but these are not terminal, but on the back of the last segment but one[351]. In that of another British moth, N. ziczac F., there are three dorsal prominences, one near the anus, and two more in the middle[352]. Some Geometers (G. fuliginosa, &c.) have two erect horns on the eleventh segment, and others (G. syringaria, &c.) two recurved ones on the eighth[353]. I must not here omit to mention the curious hooks emerging from two tubercles on the back of the eighth segment of the ferocious larva of that beautiful tiger-beetle, the Cicindela campestris L., not uncommon on warm sunny banks. This animal with incessant labour, as we are informed by M. Desmarets, digs a cylindrical burrow, to the enormous depth, the size of the animal considered, of eighteen inches. To effect this, it carries out small masses of earth upon its large concave head; and having often occasion to rest in ascending this height, by means of these hooks[354] it fixes itself to the sides of its burrow, and, having finally arrived at its mouth, casts off its burthen. When these insects lie in wait for their prey, their head, probably in conjunction with the first segment of the body, accurately stops the mouth of the burrow, so as to form an exact level with the surrounding soil; and thus careless insects, walking over it without perceiving the snare, are seized in a moment and devoured[355].

Another kind of appendage, which is found in some[Pg 153] larvæ, is the organ employed by them to carry the excrement; with which, instead of letting it fall to the ground, they form a kind of umbrella to shelter and probably conceal them. All the tortoise-beetles (Cassida L.) have instruments for this purpose, as well as an Indian genus (Imatidium Latr.) very nearly related to them. This instrument is a kind of fork, half as long as the body, consisting of two branches, growing gradually smaller from the base to the summit, where they terminate in a very fine point, of a substance rather horny, and attached to the body near the anal orifice. They are armed on the outside with short spines, from the base for about a third of their length. When this fork, as it usually is, is laid parallel to the back, with its points towards the head, the anal aperture points the same way. When the animal walks, the fork points the other way, and is in the same line with the body, and the anus assumes a prone position[356].

The larvæ of a genus of flies (Volucella Geoffr.) remarkable for inhabiting the nests of humble bees, are distinguished on their upper side by six long, diverging, pointed, membranous radii; placed in a semicircle round the anus[357]: what the particular use of these organs may be, has not been conjectured. Another in my collection has only four upper radii, but below the anus are two fleshy filiform tentacula. One of a Tipulidan described by Reaumur, has also four upper teeth; but instead of two subanal tentacula, has six[358]. The singular larva of another of this tribe (Chironomus plumosus) has on the[Pg 154] two last segments four long, fleshy, filiform, flexible tentacula, often interlaced with each other; which, according to the same illustrious author, are used by the animal to fix its caudal extremity, like the geometers, that the other end may be at liberty. Besides these organs round the anus, it has also four other oval ones, of uncertain use: not to mention the two prolegs, which M. Latreille thinks are air-tubes[359]. Jointed anal organs are observable in other larvæ: those in that of a saw-fly described by De Geer (Lyda F.) consist of three joints[360]; in that of Hister cadaverinus, a carnivorous beetle, of two[361]. The larva as well as the pupa and imago of Ephemera is furnished with three long diverging multiarticulate tails, which are probably useful as a kind of rudder to assist and direct their motions. That of the smaller dragon flies (Agrion F.) is furnished with three long vertical laminæ, by moving which, as fish do their tails, from side to side, the animal makes its way in the water[362]. That singular one, also, with a hooked head, figured by Reaumur, has a single swimming lamina, or fin, shaped like a fan, and placed in a vertical position under the tail[363].

The whole circumference of the body in some coleopterous larvæ,—for instance, in that of the tortoise-beetle lately mentioned,—is surrounded with appendages like rays. These are sometimes simple, rough with very short spinous points[364]; but I have a dipterous larva, in[Pg 155] which these radii themselves are beautifully pinnated by a fringe of longish spines on each side. Reaumur has described the grub of a beetle, the genus of which is uncertain, and which feeds upon the larva of Aleyrodes Proletella, whose body is margined on each side by eight triangular fleshy mammular processes, terminating each in a bristle, which give it a remarkable aspect[365]. The curious scent-organs with which the larva of Chrysomela Populi is fringed have been before fully described; and therefore I shall only mention them here[366].

In the larvæ of the lace-winged flies (Hemerobius), and ant-lions (Myrmeleon), the anus is furnished with a small fleshy retractile cylinder, from which proceeds the silken thread that forms the cocoon inclosing the pupa[367]. Providence has many different ways of performing the same operation. From the structure of the oral organs of these animals, the silk could not conveniently be furnished by the mouth; the Allwise Creator has therefore instructed and fitted them to render it by a spinneret at the other extremity of the body.

The respiratory anal appendages of many Dipterous larvæ will be fully described in a subsequent Letter: I shall therefore now only further observe upon this subject, that although there is seldom any alteration in the form of these appendages &c. in the same species, the caterpillars of two moths (Cerura Vinula and Attacus Tau), however, are exceptions. The former, when young, has two hairy projecting ear-like protuberances, which it entirely loses, as I have myself observed, before it assumes the pupa; and the latter, in like manner, after its third[Pg 156] change of skin, is deprived of its bent thorn-like points which attend it when young[368]. It is remarkable that these last larvæ, when just excluded from the egg, are also entirely destitute of these appendages; they soon, however, appear, from slight elevations which mark their situation, and rapidly acquire their usual form[369]. Changes of a similar kind, hitherto unobserved, may probably take place in other species.

iii. Figure. I am next to consider the general figure or shape of larvæ. All of them, with but few exceptions[370], agree in having a body more or less constricted at intervals into a series of rings or segments; usually in number, twelve; often nearly equal in length, but sometimes in this respect very dissimilar[371]. The general outline or shape of the body is extremely various: most frequently it approaches to cylindrical, as in most of the caterpillars of Lepidoptera, and of the Hymenopterous tribe of saw-flies (Tenthredo L.). The next most common figure is that more or less oblong or oval one, sometimes approaching to conical, found in many of the larvæ usually called grubs; such as those of the weevil (Curculio L.) and[Pg 157] of the capricorn (Cerambyx L.), and other coleopterous tribes; of bees, and all Hymenopterous insects but the saw-flies; and also of a large number of flies (Diptera). In some the figure approaches to fusiform, as in most of the moths of the Fabrician genus Lithosia. In others, as in those of the water-beetles (Dytiscus, &c.), it approaches to an obovate shape, being widest towards the head, and terminating in a point at the anus. In others, again, it is linear; an example of which is that of Staphylinus. Some are convex, and others gibbous, above, and flat underneath; as those of Silpha, Chrysomela and many other beetles. Others are flat, both above and below, and depressed like a leaf; a remarkable instance of which has been before noticed[372]. Some are very long, as those of most Lepidoptera; others very short, as that of the ant-lion (Myrmeleon). Many other peculiarities of form in individuals might be instanced; but a dry enumeration of these would be of no great use to you. They can only be advantageously learned by the study of good figures, and by watching the actual metamorphosis of the singularly-formed larvæ that you meet with.

Instead, therefore, of any further specification of individual forms, I shall now endeavour to give you, as far as my own knowledge of them and the information I can collect from other sources will enable me, a larger and more general view of the kinds of larvæ; for analytical inquiries lose half their value and importance unless we proceed to apply them synthetically, by forming, if possible, into groups the objects with which we are individually acquainted.

Partial attempts at a synthetical arrangement with regard[Pg 158] to the larvæ of Lepidoptera and the saw-flies (Tenthredo L.) have been made both by Reaumur and De Geer. M. Latreille also has recently given a Tableau méthodique et général of articulated animals furnished with jointed legs, considered in their first state[373]. The former of these is chiefly founded upon the number of the prolegs, and the latter upon the metamorphosis, prolegs, habits, head, and parts of the mouth, without any other notice of the configuration. Mr. Wm. MacLeay, who, though young in years, is old in science and critical acumen, has started a perfectly new hypothesis upon this subject. In the progress of his inquiries into the natural arrangement of animals, particularly of insects in the Linnean sense, he has been the first to observe, that the relation which organized objects bear to each other is of two kinds; one of real affinity, and the other only of analogy, or resemblance. This important distinction, upon which I shall enlarge in a future Letter, when I come to treat of Systems of Entomology, he has applied, in a way quite original, to larvæ in general, but more particularly to those of the Coleoptera order. For the basis of his system he assumes a relation of analogy between the larvæ of Insects that in the progress of their metamorphosis assume wings, and those that do not, which form his class Ametabola, so that the prototypes of the former shall be found amongst the latter[374]. But though Mr. MacLeay appears to consider the analogy between these two as primary, he extends it in a secondary sense to the Crustacea, at least in several instances[375]. Upon this occasion[Pg 159] he very judiciously remarks, that "in terming larvæ Chilognathiformes or Chilopodiformes, it is not meant that they are Scolopendræ or Iuli, or even near to them in affinity; but only that they are so constructed that certain analogical circumstances attending them strongly remind us of these Ametabola[376]." This remark you will bear in mind while I am treating of this subject. It should seem from another part of the same paragraph, that the comparison which our learned Physiologist recommends, is between the young of the Ametabola and the larvæ of the corresponding groups of Coleoptera. This must be understood to refer chiefly to the young of the Chilopoda and Chilognatha, since they approach nearer to them in that state, having then only six legs; but the rest of the Ametabola should certainly be brought to this comparison in their adult state: and even the two former orders in that state more strongly resemble numerous coleopterous larvæ, than when they are young and much shorter. I before called your attention to the remarkable circumstance that contrasts very many larvæ of Hexapod insects that become winged in their perfect state with adult Myriapoda: namely, that in one the progress to this state is by losing their prolegs and shortening their body; while in the other, the reverse of this takes place, numerous prolegs and additional segments being gained before they arrive at maturity[377]. As the multiplication of organs is a sign of imperfection, it may be affirmed of the former of these tribes, that their progress is towards greater perfection; while that of the other may be called a degradation. As larvæ may be regarded as a stepping-stone by which approach is made[Pg 160] from the apterous to the winged tribes of Insects, it seems most consistent with general analogy that each should connect with the other in that state in which the resemblance is greatest. Now the Myriapoda resemble larvæ, as we have just seen, most when in their adult state; therefore the comparison should be between larvæ and adult Myriapoda.

Mr. MacLeay divides coleopterous larvæ into five tribes thus characterized:—

1. A carnivorous hexapod larva, with an elongate linear flattened body, having a large head armed with two sharp falciform mandibles, and furnished with six granular eyes on each side. This kind he denominates Chilopodiform, as having for its type in the Ametabola, Scolopendra L. The examples he gives are Carabus and Dytiscus.

2. A herbivorous hexapod larva, with a long and almost cylindrical body, so fashioned that the posterior extremity being curved under the breast, the animal when at rest necessarily lies like an Iulus on its side. This tribe he denominates Chilognathiform, from Iulus L. His examples are, the larvæ of Petalocerous insects, as Scarabæus L., Lucanus L. &c.

3. An apod larva, having scarcely the rudiments of antennæ, but which is furnished instead of feet with fat fleshy tubercles; which, when continued along the back and belly, give the animal a facility of moving in whatever way it may be placed. These he denominates Vermiform, from certain of the Vermes intestina and Mollusca of Linné which he has associated with his Annulosa[378]. His examples are, Curculio L. and Cerambyx L.

4. A hexapod and distinctly antenniferous larva, with a[Pg 161] subovate rather conical body, of which the second segment is longer and of a different form from the others, so as to give the appearance of a thorax. His denomination for these is Anopluriform, from Pediculus L., forming Dr. Leach's Anoplura. His examples are, Coccinella and Chrysomela L.

5. A hexapod antenniferous larva of an oblong form, having like the former vestiges of a thorax, besides two or more articulated or inarticulated setaceous or corneous appendages to the last segment of the abdomen. This tribe he calls Thysanuriform, from Lepisma and Podura L., forming M. Latreille's order Thysanura. His example is Meloe with a note of interrogation[379].

The system here stated, of naming and characterizing larvæ from the resemblance and analogy, in many cases very striking, that they bear to the apterous tribes, is a very happy and original one, and does its author great credit; yet I think in some instances, as I shall soon have occasion to point out to you, the application of it is not so happy as the first idea. But this is always the case when a new law of nature is discovered; the proper application of it is gradually developed, and it does not at all detract from the merit of the first discoverer, that all the bearings of such law do not strike him as it were intuitively.

[Pg 162]

Having, however, got the vantage-ground afforded by this discovery of my friend, let us see if by standing upon it we cannot get a tolerable generalization of the larvæ of all orders of insects that undergo a metamorphosis. But first I must observe, that as in the perfect animals, so in their larvæ, the different groups are connected by certain transition species, exhibiting characters common to two or more of them; and likewise that in many cases, which you will see as we proceed, the analogy is as strong or stronger between them and the Crustacea (and in a few instances Arachnida, and even Mollusca) than the Ametabola. My denominations, therefore, will be taken from those tribes where the analogy appears to me the most striking, and not from the Ametabola alone.

I shall begin by drawing up for you a list of the Primary forms that I seem to have observed, and their characters; and then going through the orders, shall give you the examples of each, with such observations upon them as the case may require.

Primary Forms of Larvæ.

Characters.

1. Anopluriform. Carnivorous; hexapod; antenniferous: with a shortish oblong depressed body, and distinct[Pg 163] thoracic shield. Example: Psocus, Coccinella, most Hemiptera[380].

2. Thysanuriform. Polyphagous; hexapod; antenniferous: body with segments of trunk distinctly marked; anus often furnished with setæ or mucro. Ex. Meloe[381]? Thrips, Aphis.

3. Chilopodiform. Carnivorous; subhexapod; antenniferous: body depressed, elongate, linear, with falcate acute mandibles, a distinct thoracic shield, and an anal proleg. Ex. Cicindela[382]? Carabus L.

4. Chilognathiform. Herbivorous; body subcylindrical, elongate, linear; no thoracic shield; often many prolegs, sometimes a retractile one, and sometimes none.—Ex. Elater, Petalocera, most Lepidoptera, Tenthredo L.[383]

5. Vermiform. Polyphagous; apod or hexapod: with very short legs; antennæ nearly obsolete; body fleshy, plicate, with sides often plicato-papillose;[Pg 164] no distinct thoracic shield. Ex. Curculio L., Cerambyx L., Musca L., and many other Diptera[384].

6. Araneidiform. Carnivorous; hexapod: body very short; mandibles long, suctorious; animal lying in wait for its prey in a pitfall it has prepared; motion retrogressive. Ex. Myrmeleon L.[385] Cicindela?

7. Isopodiform. Saprophagous; hexapod; antenniferous, with longer antennæ: body oblong; thoracic shield distinct; anus styliferous or laminiferous. Ex. Blatta L. Silpha L.?

8. Onisciform. Herbivorous; polypod; antenniferous: body short, oblong, depressed, margined. Ex. Erycina, Lycæna, in the Lepidoptera, and some species of Tenthredo L.[386]

9. Idoteiform. Subcortical; hexapod; antennæ obsolete: body much depressed, with the last segment elongate, terminating in three or more mucros. Ex. Larva from Brazil. Perfect insect at present unknown.

I have placed this larva, which was described above[387], amongst crustaceous forms, because of the remarkable resemblance which the last segment of the body bears to that of the Idoteidæ; but I do it with considerable hesitation, since in other respects its type seems to be in the Ametabola. In its want of antennæ, very short legs, and ventral asperities, it resembles some of the Vermiform larvæ; in its small head, distinct thoracic shield, and oblong shape, it approaches the Anopluriform; and in its[Pg 165] very depressed body, but not at all in other respects, the Chilopodiform. At any rate, it appears of a primary Type.

10. Læmodipodiform. Herbivorous; hexapod; antenniferous, with long antennæ: body elongate, subcylindrical; second segment of the trunk the longest; anterior pair of legs distant from the other two. Ex. Phasma.

11. Amphipodiform. Herbivorous; hexapod; antenniferous, with long antennæ: body shortish, compressed, saltatorious. Ex. Gryllus L.[388]

12. Stomapodiform. Carnivorous or saprophagous; hexapod; antenniferous, with long antennæ: body elongate, subdepressed, with raptorious hands, and abdomen wider than the trunk; in aquatic species furnished with lateral gills. Ex. Mantis, Ephemera? Sialis?

13. Decapodiform. Carnivorous; hexapod; antenniferous: body elongate, narrow, convex, compressed, tapering towards the tail; tail with natatorious laminæ. Ex. Dytiscus L., Agrion F.[389]

14. Branchiopodiform. Carnivorous?; aquatic; apod; antenniferous: head distinct: body transparent, flexile, furnished with a respiratory tube just above the tail. Ex. Culex[390].

15. Limaciform. Herbivorous; apod, or with very short legs: body ovate or obovate, slimy. Ex. Apoda Haw., Tenthredo Cerasi L.

[Pg 166]

The above are the principal forms that appear to me Primary (though some doubt may rest upon the ninth and tenth); and probably others will hereafter be discovered, since at present our knowledge of the larvæ of most of the Orders is very limited. And now having given you this generalization of them, as far as they are known to me, I shall next, in a slight survey of those of the different orders, lay before you what I have further to observe upon this subject.

Coleoptera. The Anopluriform coleopterous larvæ, according to Mr. W. MacLeay's view of them, include both those of Coccinella L., Chrysomela L., and Cassida L.; but this appears to me to admit of further consideration. With regard to the two former—those of Coccinella are carnivorous, those of Chrysomela herbivorous; the first is also usually more flat and depressed. As to the latter, Cassida[391], it seems to me to belong to a peculiar type, distinguished not only by its radiated margin, but by the remarkable deflected anal fork on which it carries its excrement. At present I know no analogous form amongst the apterous tribes; I must therefore leave this without a denomination. Perhaps the larva of Hispa or Alurnus, when known, will throw light upon this subject. The larva of Endomychus agrees with that of Coccinella.

There are very few known larvæ that approach to a true Thysanuriform type in this order: that most celebrated is the one supposed to belong to Meloe; but the claim of this to be so considered, is, as we have seen, rather dubious. Should this point at last be satisfactorily ascertained, it[Pg 167] will probably carry with it the whole tribe of vesicatory beetles. But even this animal in its general structure is anopluriform: the only circumstance that gives it any analogy to the Thysanura being its anal setæ. Mr. William MacLeay is inclined to regard some of the larvæ of the Malacodermi Latr., but which of them he does not state, as probably belonging to the tribe in question[392]. Those of Lampyris and of Telephorus, as described and figured by De Geer[393], appear to me intermediate between the Anopluriform and Chilopodiform Types: they have no anal setiform or styliform appendages, their mandibulæ are falcate, and their habits seem carnivorous.

Examples of Chilopodiform coleopterous larvæ are more numerous. Of this description are those of Gyrinus, Cicindela, Carabus, and Staphylinus. That of the first, indeed, appears to be the most perfectly Scolopendriform of any yet known; yet the gills or respiratory laminæ, a pair of which issues from each abdominal segment, and two pair from the last[394], prove that there is no slight analogy between it, and indeed many other aquatic larvæ, and the Stomapoda amongst the Crustacea. A remarkable instance of analogy with the Decapoda of the same Class is presented by the larva of Dytiscus, &c. which Mr. MacLeay considers as Chilopodiform, but which exhibits no other resemblance to Scolopendræ than[Pg 168] in its predaceous habits and threatening aspect. Its convex, compressed, tapering body, terminating in setæ or laminæ, is certainly much more like that of a shrimp or a prawn; to which the older Entomologists thought it was akin[395], and after which they named it. As Mr. MacLeay's object was, to take all his forms from the Ametabola, perhaps these larvæ will best fall in with his Chilopodiform type; though in the general form of their body they most represent a section (Lepisma L.) of the Thysanura.

Chilognathiform forms are equally numerous in the Coleoptera with the preceding. The wire-worm, or larva of Elater Segetis, as to shape best represents the full-grown Iulus[396], and those of the Petalocera (Scarabæus L., Lucanus L.) the young one.

The most abundant of all forms in this order, is, I think, the Vermiform, upon which I have nothing further to remark.

With regard to Crustaceous forms in Coleoptera, besides the Decapodiform just noticed, I possess two specimens of larvæ of Silphidæ which seem to exhibit a considerable analogy with the Isopodous Crustacea, one rather[Pg 169] convex and the other flatter, so as to give the idea of an Armadillo and of an Oniscus.

Strepsiptera. Larva Vermiform.

Dermaptera. Larva Thysanuriform. Type Podura or Sminthurus.

Orthoptera. Mr. MacLeay considers the larvæ of this Order as primarily Thysanuriform[397], though he allows the resemblance between them and Amphipoda to be particularly striking[398]. For my own part, their prototypes appear to me to be in the Crustacea, and their analogical relations to the Thysanura much more distant. I trust this will appear to you the reverse of dubious in a progress through the Crustaceous Orders. I begin with the Isopoda. Take the larva of a Blatta, and place it between a Lepisma, or Machilis, and an Oniscus, or Porcellio; you will find that in shape and width, and the form of its anal styles, it resembles the latter much more than it does the former, with which it possesses scarcely any character in common, except its multiarticulate antennæ. It is remarkable, that amongst the Blattidæ we meet with species that represent both the Oniscidæ and Armadillo or Glomeris[399], the latter being more convex than the former. In their habits the Blattæ certainly agree with Lepisma; and Dumeril, who thought the latter and Podura subject to a metamorphosis, imagined they were related[400].

The Spectres of Stoll (Phasma F.) are so strikingly analogous to another crustaceous tribe, the Læmodipoda, particularly the genus Caprella, that Montagu gave one species the Trivial name of Phasma[401]. The jumping[Pg 170] Amphipodiform Crustacea are represented extremely well by Gryllus L., and the Stomapodiform, particularly Squilla Mantis, by Mantis. The resemblance in this last instance is so very striking, that it cannot escape the eye of the least intelligent observer. Orthopterous insects may perhaps one day be discovered analogous to the two other crustaceous orders, the Decapods and Branchiopods; but at present I know of none of that description.

Hemiptera. The larvæ of this order, which in general resemble the perfect insect, except that they have no wings, seem most commonly to belong to the Anopluriform type[402]; but the Aphides, Chermes, and Thrips may, I think, be regarded as more analogous to the genera Podura and Sminthurus in the Thysanura[403]. I have some suspicion that the Nepidæ, Naucoris, and the remipedes, Notonecta, Sigara, &c. may find their prototypes amongst the Crustacea; but my confined knowledge of the latter does not enable me to point to any individual genera or tribes that they may be presumed to represent.

Neuroptera. As the kinds of larvæ of the different tribes composing this order, as it now stands, are very various, it is to be expected that the analogical forms they represent are equally so. The Libellulina MacLeay (whose metamorphosis that gentleman has denominated subsemicomplete, a term warranted by their losing in their perfect state the mask before described[404]) in their oral organs, particularly by their galeate maxilla and distinct ligula[405], have some relation to the Orthoptera, the prototypes of whose larvæ we have found amongst the[Pg 171] Crustacea: probably, therefore, those of the tribe in question lurk in that class; a suspicion that receives strong confirmation from the larva of Agrion[406], which in its tapering body and anal natatorious laminæ represents a shrimp. The larvæ of that very peculiar and distinct tribe, the Ephemerina, appear to be intermediate between the Stomapodiform and Thysanuriform types. Their natatory respiratory abdominal laminæ seem copied from the former, and their anal diverging setæ from the latter[407]. The Myrmeleonina, as well in their general form as in their motions and habits, present a most singular analogy with the tribe of spiders, as does also in some respect that of Cicindela. With regard to Panorpa, which Mr. MacLeay remarks is related to Myrmeleon[408], and is a most ferocious insect[409], as its larva has not yet been discovered, nothing certain respecting its analogical form can be asserted; but should it, like the male fly, represent the scorpion, both orders of Arachnida will have their representatives in the class we are considering. The Corydalina, as far as the larva of Hemerobius instructs us, is Chilopodiform, but with a tendency to the Araneidiform Type. The Ametabola also furnish the prototype of the next tribe, the Termitina, which, as is evident both from Psocus and Termes, are perfectly Anopluriform. The Sialina, or Plicipennes of Latreille, excluding Trichoptera Kirby, appear to me to be intermediate between the Chilopodiform and Stomapodiform Types, and not without some relation to the Thysanuriform. Their pediform, jointed, respiratory abdominal appendages, their head and falcate mandibles, seem copied from the first tribe. The same appendages[Pg 172] considered as organs of respiration, and their taper forks, are moulded upon the plan of the Stomapodiform Crustacea, and the long seta which terminates the abdomen is upon the Thysanuriform plan[410].

Trichoptera. The larvæ of this order appear also to be constructed upon a double plan. The respiratory threads observable in both the upper and under sides of the abdomen connect it with the Stomapoda, and its cylindrical elongate body with Chilognathiform types in the Lepidoptera[411].

Lepidoptera. The great majority of larvæ in this order are Chilognathiform, but there are exceptions to this remark. Those of the Geometræ recede from this type, both in their motions and the distance and number of their legs. In both these respects they represent the Læmodipoda in the Crustacea[412]. Other caterpillars are Onisciform; and a third sort seem to leave the Annulose type, and imitate that of the Mollusca, and one is figured by Madame Merian[413] which appears to tend even to the Chilopodiform type.

Hymenoptera. In this order the larvæ of the saw-flies, Tenthredo L., are in general Chilognathiform, though some are Onisciform, others Limaciform, and those of Lyda F. (Cephaleia Jur.) and Sirex[414] have a Vermiform tendency,[Pg 173] and are a stepping-stone to those of the rest of the order, which are all Vermiform and apods.

Diptera. The majority of this order may be set down as Vermiform, though it is not improbable that some of them bear an analogy to animals that appear far removed from the Annulosa. Thus, the larva of Stratyomis Chameleon seems to exhibit no small resemblance to some of the Polypi vaginati in the Acrita subkingdom of Mr. W. MacLeay[415]. That of Culex and some others is constructed on a quite different type from the rest, and seems to possess some analogy to the Branchiopod Crustacea.

Though some of these analogies are more striking than others, yet in almost all that I have stated there is that kind of resemblance that could not be the result of what is called mere chance; and Mr. MacLeay, by first pointing out this plan of the All-wise Creator, and by laying down the doctrine of analogies in general, as distinguished from affinities in the animal kingdom, has furnished the believer with a new argument against those attacks of the infidel, that would render null those proofs of the wisdom and goodness of the Author of nature with which the animal and vegetable creation furnish us; by affirming most absurdly, and under the most stultifying blindness of mind, that the creatures were in a manner their own creators, their wants under local circumstances stimulating them to efforts that in a long course of years produced all the different forms and organizations that are now to be found in our globe. The affinities and close connexion of beings with each other, so that the ascent from low to high is usually by the most gentle gradations, is the[Pg 174] circumstance on which they build this strange and impious theory. But the fact, that certain animals of one tribe were created with a view to certain animals of another, so as to present a striking aspect of correspondence, parallel almost with that of type and antitype, without any real affinity or approximation;—this triumphantly proves a Power above and without them, who has associated them not only in a complex chain of affinities, but has caused them to represent and figure each other, even when evidently far removed, so as to give a mutual correspondence and harmony to the whole, which could be produced only by a Being infinite in power and wisdom, who made all things after a general preconceived plan and system.

iv. We are now to consider the clothing with which larvæ are furnished. Many are quite naked, and smooth or rough only with granular elevations or tubercles orderly arranged; but a very considerable number, especially of the Lepidoptera order, are clothed with hair or bristles of different kinds, in greater or less abundance, and arranged in different modes; and a proportion still smaller have their skin beset with spines or a mixture of spines and hairs. Lyonnet found that the hairs of the caterpillar of the great goat-moth (Cossus ligniperda) were hollow, though not to the apex: probably this is the case with those of other larvæ, as well as with their spines. In this instance they were set, he observes, in a corneous ring, or very short cylinder, elevated a little above the skin. The hair passes through this ring, and appears to be rooted in a soft integument, which clothes the skin within, and upon which the nerves form a reticular tissue,[Pg 175] some of which he thinks he has even seen enter the root of the hairs, which perhaps are organs of touch[416].

Of the pilose larvæ, some, like most of those of the smaller moths (Geometra, Tortrix, Pyralis, &c.), have merely a few scattered short hairs, scarcely perceptible except through a lens: others (Odenesis potatoria, Lasiocampa Rubi) are covered with down more or less thick: in others (Eriogaster lanestris, Lasiocampa Neustria) the hair is slenderer, and more like wool; the body of two species which I purchased from the collection of Mr. Francillon is covered with woolly hairs, so long as to give them the appearance of a shock-dog; and Madam Merian has figured a similar one, which she could not bring to the perfect state[417]. The hairs of many Bombycidæ, known commonly by the name of hairy caterpillars, as Arctia erminea, &c. are stiffer, resembling bristles; sometimes, as in Arctia chrysorhea, mixed with shorter ones. The hairs either spring immediately from the skin (Noctua Aceris, leporina), or, as is more general, proceed only from certain tubercular elevations, usually subhemispherical, but sometimes conical; of which a number varying from four to twelve are found on each segment of different species. They seem to issue from these tubercles, as little diverging streams from the rose of a watering-pot. In both cases, they form a coating usually so dense as to conceal the body, but sometimes more thinly set, and admitting the skin to be seen more or less between them. In a caterpillar of the beautiful Arctia ocularia, the hairs are set upon tubercles alternately nearer the anterior and posterior margin of each segment, so as to form a dense[Pg 176] band, the rest being naked; and in the lovely green and black one of Saturnia Pavonia, each tubercle bears but six hairs, diverging like a star, the central one being the longest and capitate, so that the chief part of the body appears naked. This diverging position of the hairs is most common in the thick-clothed larvæ also, but many have them placed differently: thus, in those of Callimorpha Caja and Arctia villica[418] they are all directed towards the tail, like the quills of a porcupine: in some others the anterior ones point towards the head: in that of Eriogaster Quercus half of the tuft of hairs of each tubercle is directed downwards, the other half upwards: in that of Arctia Salicis all the hairs point downwards, so that the belly is thickly covered, while the back is bare. Another variation is, that the hairs of half the tubercle are sometimes very long, while those of the other half are very short, and even of a different colour[419]. In the larva of Tussuck moths (Laria pudibunda, fascelina, &c.) the hairs are collected into tufts of a singular appearance, those on the intermediate segments of the back being quite level at the top, so as to resemble so many brushes; while those on the first and last segments are longer, and composed of feathered hairs converging to a point at their extremity, like a common camel-hair-pencil[420]. This last mode of arrangement prevails also in the larva of Noctua Aceris; but in this the pencils are shorter, exactly wedge-shaped, and distinguished by another particularity, that of springing directly from the[Pg 177] skin, and not from a tubercle. This is also the case with the large caterpillars of Odenesis potatoria, which has a double row of short bundles of black hairs on the back, intermixed with larger ones: at each end of the body is a pencil of converging hairs, and the sides are spotted with bundles of white ones, which with longer tawny ones are bent downwards, so as to cover the sides of the creature[421]. Some have the anterior aigrettes disposed like the arms of a cross, of which the body of the caterpillar is the stem[422]. But not only is there considerable variety in the general arrangement of the hairs that clothe our little larvæ, the hairs themselves differ much in their kind and structure, of which I will now, before I proceed to consider spines, give you some account. Several of them are feathered like the plumes of a bird: this is the case with those of Morpho Idomeneus, on each segment of the body of which are three blue tubercles, like so many little turquois beads, from each of which proceeds a long black plume[423]. Other hairs terminate in a club; those of the larva of Noctua Alni, a specimen of which I possess taken in England, are flat and incrassated at the apex, something like the antennæ of some Sphingidæ. Mad. Merian has figured the caterpillar of another moth which feeds upon the Papaw-tree (Carica Papaya) with similar hairs[424]. But the most remarkable larva for the shape of its hairs is that of Anthrenus Musæorum, the little pest of our cabinets,[Pg 178] which I noticed in a former letter[425]. All the hairs of its body are rough with minute points; but those of six diverging long tufts or aigrettes, laid obliquely on the anal extremity of the body, which the animal when alarmed erects as a porcupine does its quills, are of a most singular structure: every hair is composed of a series of little conical pieces, placed end to end, the point of which is directed towards the origin of each hair, which is terminated at the other extremity by a long and large conical mass, resembling somewhat the head of a pike[426].

Besides the one lately mentioned, other caterpillars are rendered striking by the brilliant colour of the tubercles from which their hairs emerge. A remarkable instance of this is the thick large caterpillar of a Bombyx, which feeds upon the Psidium pyriferum, or white Guava, figured by Madame Merian. This caterpillar, which is white, with transverse black stripes, and which has two singular long converging curved bunches of hairs near the tail, is splendidly adorned on each side with fifty red tubercles, shining like coral, from which proceed six or seven long diverging hairs. Leeuwenhoeck took these tubercles for eyes[427]. Another figured by the same lady, who mistakes it, with her usual inaccuracy, for the larva of a Lygæus F., and which seems by her description to be between the onisciform and limaciform types, has the apparently fleshy mamillæ that project from its sides and back crowned with little hairy red globes, which give the animal a most singular and unique appearance[428]. Having thus described some of the principal modes in which[Pg 179] the All-wise Creator has decked and defended these creatures with hairs, I shall next give you a short account of the spines with which he has armed others. The spinous larvæ are principally lepidopterous, and more particularly conspicuous in some tribes of the genus Papilio L., though some saw-flies and Diptera are also distinguished by them. Vanessa Io[429], Atalanta and Urtica, Argynnis Paphia, Urania Leilus, and many other Butterflies, &c. are clothed with long sharp points, which claim the denomination of spines, rather than that of hairs or bristles; being horny and hard, and so stiff at the point as readily to pierce the skin. Those of the last-mentioned species, Madame Merian says, are as stiff as iron-wire[430]. They are sometimes entirely simple, and look like spikes rather than spines, as in the caterpillar of Nymphalis Amphinome and Morpho Menelaus[431]; but ordinarily they are beset with hairs, or more commonly with shorter spines, which often give them the appearance of plumes, as in Urania Leilus just mentioned: sometimes these lateral spines are so long as to have the appearance of a branch of a tree; this is strikingly the case with a small caterpillar which Captain Hancock brought from Brazil; its body is so thickly planted with spines of this description, that it absolutely wears the appearance of a forest or thicket in miniature. A singular circumstance attends the spines of this species: in many cases a smaller and very slender hair-like spine issues from them, resembling a sting; and this accounts for an observation of Abbott's, that many American caterpillars sting like a nettle, raising little white blisters on the skin[Pg 180] when accidentally or slightly touched[432]. Lewin has described the caterpillar of a moth found in New Holland, which he names Bombyx vulnerans, that, like these Americans, has also the power of wounding, but in a different way. It darts out, he says, when alarmed by the approach of any thing, from as many knobs or protuberances in its back eight bunches of little stings, with which it inflicts a very painful and venomous wound[433]. The caterpillar of Papilio Protesilaus F., if Madame Merian's account and figure of it are correct, has its body armed with hairy spines, the extreme point of which is surmounted by a star-shaped appendage[434]. Those of a few saw-flies (Tenthredo Pruni L.), and another figured by Reaumur[435], are covered with a little forest of spines without lateral branches, but divided into a fork at the apex. Some spines are merely rough, with very short points, as those round the head, which give so terrific an appearance to the caterpillar of the Bombyx regalis, of some proceedings of which I gave you an account in one of my former letters[436].

I must now say something upon the arrangement of these spines. Though in a few instances so thickly set as entirely to conceal the body of the animal, as in the case of the Brazil one lately mentioned, yet generally speaking, even when they are most numerous, they permit the skin to be distinctly seen. Their arrangement is various, though always orderly: in the majority they[Pg 181] are planted singly, but in some caterpillars in bundles. In that of Saturnia Io, on each segment there are six bundles of longish, quill-shaped, sharp, slender, diverging spines, which also appear to sheath aculei. Madame Merian has figured this larva, or one very near it, as the grub of a Euglossa[437], with which, though she affirms she traced it to the fly, it can have no connection. With regard to number, some larvæ have only four spines on each segment; others five, others again six, and others seven, or even eight: they are planted on the sides and back only, never on the belly. They are often more numerous on the intermediate than on the anterior and posterior segments; but sometimes the reverse of this takes place; in that of Attacus Erythrinæ only the head and tail are armed with spines, the rest of the body being without any[438]; and in that of Morpho Teucer there is only a single spine on the four intermediate segments[439]. They are usually all nearly of equal length; but in some cases those of the head and tail are much longer than the rest, and remarkably so in the caterpillar of Urania Leilus, also beautifully plumose, and gracefully waved[440]. Those in the second and third segments are much longer than any of the rest in that of Bombyx regalis; which circumstance gives it the terrific appearance lately alluded to. In the family to which Argynnis Paphia belongs, the larva is adorned with two on the back of the first segment twice as long as the rest, and resembling at first sight two antennæ.

The spines, as well as the hairs of the new skin, are concealed under the old one, and not incased in its spines;[Pg 182] but Bonnet ascertained, that if cut off very closely, the larva sometimes died in consequence, whilst no such result followed a similar operation on hairy larvæ. We learn from Reaumur[441], that some spinous larvæ of saw-flies (Tenthredo L.) lose their spines at the last change of their skin; and from Madame Merian, that that of Attacus Erythrinæ before mentioned loses also at the same period the six tremendous black spikes that arm its black and yellow larvæ. The grubs of ants that are destined to pass the winter in the larva state are hairy, but are not so in summer[442]. The spines found in the grubs of some gad-flies (Œstrus L.) are of a different kind from those above described, being very minute triangular flat plates, arranged in different and contrary directions[443], and serving the insect merely to change its place and fix itself[444].

Two other kinds of clothing, if so they may be called, neither coming under the description of hairs nor spines, are found in some other larvæ, not only amongst the Lepidoptera, but also in some of the other orders. Nymphalis Populi and others of the same family have larvæ furnished on the back of each segment with cylindricoconical processes of a fleshy substance, obtuse at the apex and surrounded with capitate hairs. In that of N. Sybilla, which has on each segment two fleshy protuberances, they are bifurcate or trifurcate, and also encircled at the base with a hairy tuft[445]. Others, as those of Melitæa Artemis, Cynthia, &c. have each segment beset on the back with from seven to nine fleshy, pubescent, wedge-shaped protuberances; two larger ones projecting[Pg 183] over the head. Under this head, too, may be noticed, the glutinous secretion which clothes the grub of Cionus Scrophulariæ, a little weevil; and of Tenthredo Cerasi L. a saw-fly, and that waxy or powdery substance which transpires through the skin of the larvæ of several Aphides, Chermes, Cocci, Hylotoma ovata F., &c. The Aphis, whose extensive ravages of our apple-trees (A. lanata) were before described to you[446], is covered and quite concealed by this kind of substance, so that the crevices in the bark which they inhabit look as if they were filled, not with animals, but with cotton. The insect, also, that forms those curious galls produced upon the spruce fir, and which imitate its cones (Chermes Abietis L., Aphis De Geer) secretes a similar substance. In these and other cases of the same kind, this matter seems to be, if I may so speak, wire-drawn through numerous pores in certain oval plates in the skin, more depressed than the rest of the back, arranged regularly upon the segments, and exhibiting minute tuberosities. When young, these animals have more of this secretion than when more advanced: it then hangs from their anal extremity in locks[447].

But the insects most remarkable for a covering of this nature are those Coccidæ of which Bosc has made a genus under the name of Dorthesia. De Geer is the first author that notices them, and has given a description and figure of one species under the name of[Pg 184] Coccus floccosus[448]. It was discovered by Modeer upon some sere fir-leaves in a thick bed of moss. Panzer has figured a second found upon Geranium sanguineum, which from the figure appears distinct from De Geer's, under the name of Coccus dubius[449]. Fabricius regards this as synonymous with the Dorthesia characias of Bosc, inhabiting Euphorbia characias in South Europe[450]. Olivier found a species upon the bramble[451]. I once took one, which appears to differ in some respects from the preceding species, upon Melampyrum cristatum, and our indefatigable friend Mr. Sheppard has sent me another, on what plant found I do not remember, which does not agree with any that I have mentioned. The body of the animals of this genus is covered by a number of cottony or waxy laminæ which partly cover each other, and are arranged usually in a triple series: in De Geer's figure the series appears quadruple, the lateral ones being placed obliquely. The anterior one in my specimen covered the head, and they are all canaliculate. Above the anus are four diverging ones: the whole are of the most dazzling whiteness. When these laminæ are removed, the body appears divided into segments.

With respect to those larvæ which imitate slugs by the viscid covering that besmears them and issues from their pores, we learn from Professor Peck that this exudation takes place as soon as they are hatched; that the animal retains its humidity although exposed to the fiercest heat of the sun, and that at the last moult the skin becomes[Pg 185] quite clean, and free from all viscidity[452]. It is probable that the other limaciform larvæ are similarly circumstanced. Madame Merian has figured an onisciform one, the legs of which, she says, are covered with a viscid skin: this produced a Noctua. Those of Papilio Anchises also are slimy, and adhere to each other[453].

v. Amongst other qualities which attach to larvæ, we must not omit to say something concerning their Colour. For though those which live in darkness, in the earth, in wood, in fruits, &c. are, with few exceptions[454], of an uniform whitish colour, yet such as are exposed to the influence of the light are usually adorned with a vast variety of tints, sometimes the most vivid that can be imagined. That the white colour of the former may be attributed to the absence of light is proved by an experiment of M. Dorthes, who having forced some to live under glasses, exposed to the light, found that they gradually became brown[455]. To attempt any classification of coloured larvæ would be in vain, since they are tinged with almost every possible shade that can be conceived, of many of which it would be difficult to find examples elsewhere; and infinitely diversified as to the arrangement and figure of their multiform markings and spots. A few general remarks, therefore, are all that you will expect on this head. Many are of one uniform colour; while a variety of tints, very different, and very vivid and distinct, ornament others. Sometimes they are distributed in[Pg 186] longitudinal rays or bands, at others in transverse ones. Sometimes they are waved or spotted, regularly or irregularly; at others they are sprinkled in dots, or minute streaks, in every possible way. Various larvæ are of the colour of the plant on which they feed, whence they are with difficulty discovered by their enemies. Thus, a large proportion of Lepidoptera are green of different shades, sometimes beautifully contrasted with black bands; a circumstance which renders the caterpillars of two of our finest insects of this order as lovely as the fly: I mean that of Papilio Machaon and Saturnia Pavonia. Very frequently the larvæ of quite different species resemble each other so exactly, in colour as well as shape, as scarcely to be distinguishable: this sometimes takes place even where they belong to different genera, as in those of Bombyx versicolor a moth, and Smerinthus Populi a hawk-moth. And it sometimes happens, very fortunately for distinguishing allied species, that where the perfect insects very nearly resemble each other, the larvæ are altogether dissimilar. Thus, the female of Pieris Rapæ is so much like the same sex of Pieris Brassicæ, that it might be taken for a variety of it, did not the green caterpillar of the one, and the spotted one of the other, evince the complete distinction of these butterflies. Noctua Lactuca, N. umbratica, and several other species of the same tribe, which includes N. Absinthii, Verbasci, Chamomillæ, Abrotani, are so extremely alike, that the most practised eye can scarcely discover a shade of difference between them, though their larvæ in colour and markings are constantly distinct[456]. The markings of[Pg 187] species belonging to the same family are usually different; but in some cases the latter may be prejudged from the former. The larvæ of many of the genus Sphinx L., for example, have their sides marked by oblique streaks running from the back in a direction towards the head; and by this last circumstance they are distinguished from those of Bombyx versicolor, Attacus Tau, and others of the same tribe, which have also lateral oblique striæ, but running from the back towards the tail[457]. The colours of individual larvæ of the same species are usually alike, but in Sphinx Elpenor and some others they vary exceedingly. Many, like those of Lasiocampa Rubi, Saturnia minor, &c., are of one colour when first disclosed, and assume others quite different in riper age. Just previously to changing their skin, the tints of most larvæ become as dull and obscure, as they are fresh and vivid when the change has fully taken place; and in some instances the new skin is quite differently marked from the old one. This is remarkably the case with the last skin of some of the larvæ of the genus Tenthredo L., which is entirely different from all the preceding ones. As people when they advance far in years usually become more simple in their dress than when they were young, so the larvæ in question change an agreeably variegated skin for one of a uniform and less brilliant colour[458]. Madame Merian has observed with respect to Attacus Erythrinæ, that its caterpillar is at first yellowish, with nine black striæ on each side: when arrived at one third of its size, they become orange; the striæ are obliterated, and in their place a round black spot appears on each of the[Pg 188] eight intermediate segments[459]. Mr. Sheppard has remarked to me, that the skin of that of Sphinx Ligustri, after being under ground four days, was changed from a vivid green to a dull red. Very rarely, however, it becomes of a more brilliant hue just before entering the pupa state: thus, that of another hawk-moth (Smerinthus Tiliæ) changes to a bright violet; and the yellow hairs of that of Laria pudibunda then become of a lovely rose colour. And here I may observe, that the hairs and spines also, of larvæ, vary greatly in colour. They are to be met with brown, black, red, yellow, violet, white, &c. De Geer found, that in the larva of Cimbex nitens the two sides of the body were of a different colour, the left being of a deep green, whilst the right side and the rest of the body were paler[460]; but as he saw only a single individual, this was probably an accidental circumstance. Though the caterpillars, as I lately said, of one of the most beautiful butterflies and moths that inhabit Britain contend with the perfect insect in loveliness, yet in general no judgement can be formed of the beauty of the future fly from the colour of the larva; and the young Aurelian must not flatter himself always with the hope, because the caterpillar excites admiration by its colours and their arrangement, that the butterfly or moth it is to produce will do the same; nor ought he to despise and overlook a sombre or plain-coloured individual of the former, under the idea that it will produce one equally plain of the latter, for it often happens that the splendid caterpillar gives a plain butterfly or moth, and vice versâ. De Geer, however, gives us two instances of conformity[Pg 189] between the colours of the caterpillar and those of the future moth; the one is that of the common currant-moth (Phalæna G. grossulariata L.), the caterpillar of which is white, ornamented with several black spots varying in size. At the two extremities it is yellowish, with a longitudinal ray of the same colour on each side, the head and legs being black. These colours are all to be found in the fly, the ground of its wings being white ornamented with many black spots of different sizes. Its upper wings are traversed by a yellowish band; and towards their base is a spot of the same colour. Its body is yellowish, with black spots; but the head and legs are black[461]. The other is that of a green caterpillar, which gives a green moth, figured by Reaumur (Pyralis prasinaria Fab.)[462]. Sometimes, also, the sex of the future perfect insect may be predicted from the colour it exhibits in its first state: thus, the brown caterpillars of Noctua Pronuba produce males, and the green ones females[463]. The sexes, also, of N. exoleta and Persicariæ differ in that state.

vi. To the full account of the Food of insects given in a former letter[464], which had reference chiefly to their larva state, it is only necessary in this place to add a few particulars not there noticed. Many larvæ when first excluded, as those of Pieris Cratægi, &c. devour the shells of the eggs from which they have proceeded[465]; and[Pg 190] others (Cerura Vinula, Sphinx Euphorbiæ, Noctua Verbasci), though their usual food is of a vegetable nature, eat with great apparent satisfaction the skins which they cast from time to time, not leaving even the horny legs. This strange repast seems even a stimulating dainty, which speedily restores them to vigour, after the painful operation by which they are supplied with it. Under this head it will not be out of place to mention, that some larvæ of insects, which feed only on the juices of animals, or the nectar and ambrosia of flowers, have no anal passage, and of course no feces. This is said to be the case with the grubs of bees, wasps, the larvæ of Myrmeleon, &c.[466]

vii. You will require no stimulus to induce you to attend to the subject I am next going to enter upon,—the Moulting, namely, of Larvæ; or their changes of skin. This, indeed, is a subject so replete with interest, and which so fully displays the power, wisdom, and goodness of the Creator, affording at the same time such large occasion for nice investigation, that a pious and inquisitive mind like yours cannot but be taken with it. In the higher orders of animals, though the hairs of quadrupeds and the feathers of birds are in many cases annually renewed, the change, or scaling and increment of the skin, is gradual and imperceptible; no simultaneous rejection[Pg 191] of it, in which it is stripped off by the animal itself like a worn shirt, being observable, till you descend in the scale to the Serpent tribe[467], which at certain periods disengage themselves from their old integument, and start forth with that new and deadly beauty so finely described by the Mantuan bard:—

In these the new skin, I imagine, is formed under the old from the rete mucosum; but in insects, as I formerly stated[469], since the time of Swammerdam it has generally been believed by entomologists, that the larva includes a series of cases or envelopes, one within the other, containing in the centre the germe of the future perfect insect, whose development and final exclusion take place only when these cases have been successively cast off. This hypothesis, as was explained to you on a former occasion[470], has been controverted by a late writer, Dr. Herold; who affirms that the skins of caterpillars are also successively produced out of the rete mucosum. I have however, I hope, satisfied you that the old system is most consonant[Pg 192] to nature and probability: but as we are now to enter at large upon the Moults of insects, it will not be without use if I add a few additional reasons which seem to me still further to prove the correctness of Swammerdam's system, as far as it relates to that subject. With regard to the mere formation of the skin from the rete mucosum, were this the whole question few would hesitate to adopt the sentiments of M. Herold; but when we come to consider further—that the number of moults of individuals of the same species is always the same, and that it varies in different species, and takes place at certain periods,—we begin to suspect that something more than the mere formation of a new skin upon an old one being cast is to be accounted for; and that the law which prescribes its own definite number of skins to each species, must begin to act in the primordial formation of the larva. Again, the hairs observable in the higher animals do not take their origin from the epidermis solely, but are planted below it in the rete mucosum, or deeper[471]; so that the change of skin does not affect them; but in the larvæ of insects they are a continuation of that integument, since, when the moult takes place, they always remain on the rejected skin[472]: this is the case, also, even with spines. If you shave a caterpillar ready to change its skin, either partially or generally, you will find that the parts in the new skin that correspond with those that are denuded, are equally hairy with those that were not[473]; and if you pay attention to the new-clad animal, you will find further, that the hairs never grow after a moult. From[Pg 193] hence it follows, that the hairs have their place and take their whole growth between the new skin and the old[474]. Whether the spines, simple or compound, lately described to you, that arm some larvæ are similarly circumstanced, seems not as yet to have been ascertained; but as the spinous ones of certain Tenthredines L. and Lepidoptera at their last moult have no spines, the presumption is, that, whether incased or not, they are mere appendages of the skin on which they appear. A new set of hairs, therefore, and probably of spines in spinous larvæ, accompanying each skin, and these varying very much in size, composition, &c. though a new membrane may be admitted to be formed from an action in the rete mucosum without a pre-existent germe of it, it seems not easy to conceive how these hairs and spines can spring up and grow there, each according to a certain law, without existing previously as a kind of corculum or punctum saliens; and that the germes of the tubercles, in which the hairs are so generally planted, according to a certain arrangement and in a given number, should also pre-exist, seems most consonant to reason. These and the several skins may all co-exist in their primordial germes, and remain beyond the discovery of our highest powers of assisted vision, till a certain period when they may first enter the range of the microscope-aided eye. It does not therefore follow, because these primordia semina rerum are not discoverable, that therefore they may not exist. Our faculties and organs are too limited and of too little power to enable us to see the essences of being.

Upon the supposition that the hypothesis of Swammerdam[Pg 194] is the true one, we may imagine that the envelope that lies within all the rest is that which covers the insect in its pupa state. Above this are placed several others, which successively become external integuments. These changes or casting of the skin in larvæ, analogous, as before observed, to that of serpents, are familiar to every breeder of silk-worms, in which four such changes occur: the first at the end of about twelve days from its birth, and the three next each at the end of half that time from the moulting which preceded it. With some exceptions[475], similar changes of the skin take place in all larvæ, not however in the same number and at the same periods. Most indeed undergo this operation only three or four times; but there are some that moult oftener, from five up to eight (Arctia villica), nine (Callimorpha Dominula), or even ten times; for so often, M. Cuvier informs us, the caterpillar of the tiger-moth (Callimorpha Caja) casts its exuviæ. It has been observed that the caterpillars of the day-flying Lepidoptera (Papilio L.) usually change only three times, while those of the night-flying ones (Phalæna L.) change four[476]. The periods that intervene between each change depend upon the length of the insect's existence in the larva state. In those which live only a few weeks or months, they are from eight to twenty days; while in those that live more than a year, as the cockchafer, &c. they are probably proportionably longer: though we know very little with[Pg 195] regard to the moult of any insects besides the Lepidoptera.

A day or two previously to each change of its skin, the larva ceases eating altogether; it becomes languid and feeble, its beautiful colours fade, and it seeks for a retreat in which it can undergo this important and sometimes dangerous and even fatal operation in security. Here, either fixing itself by its legs to the surface on which it rests, or, as is the case with many caterpillars, by its prolegs, to a slight web spun for this purpose, it turns and twists its body in various directions, and alternately swells and contracts its different segments. The object of these motions and contortions seems to be, to separate the exterior skin, now become dry and rigid, from the new one just below it. After continuing these operations for some hours, resting at intervals without motion, as if exhausted by their violence, the critical moment arrives: the skin splits in the back, in consequence of the still more violent swelling of the second or third segment: the opening thus made is speedily increased by a succession of swellings and contractions of the remaining segments: even the head itself often divides into three triangular pieces, and the inclosed larva by degrees withdraws itself wholly from its old skin. All larvæ, however, do not force their way through this skin in precisely the same place. Thus, those of the hawthorn butterfly (Pieris Cratægi), according to Bonnet[477] make their way out by forcing off what may be called their skull, or the horny part of their head, without splitting the skin, which remains entire; others have been observed to make their way out at the side and the belly. Reaumur[Pg 196] noticed the larva of Zygæna Filipendulæ, previously to its last moult, actually biting off and detaching several portions of its old skin; and before this, drops of a fluid resembling water were seen to exude from it[478].

The skin when cast is often so entire, that it might be mistaken for the larva itself; comprising not only the covering of the main trunk with the hairs which clothed it, but of the very skull, eyes, antennæ, palpi, jaws, and legs; which, if examined from within, are now found to be hollow, and to have incased, like so many sheaths, similar parts in the new skin. That the feet of the newly-coated larva were actually sheathed, as fingers in a glove, in the same parts of the exuviæ, may be proved by a very simple experiment: if a leg of one just ready to cast its skin be cut off, the same limb will be found mutilated when that change has ensued. The anal horns, also, of the larvæ of the hawk-moth (Sphinx L.) and other similar protuberances, are incased in each other in like manner; but hairs are laid flat between the two skins, and contribute considerably towards their more easy separation. Thus, if you saved the skins cast by the larva of Callimorpha Caja, for instance, you would appear to have ten different specimens of caterpillars, furnished with every external necessary part, and differing only in size, and the colour perhaps of the hairs, and all representing the same individual.

But further changes than this take place. Swammerdam says, speaking of the moult of the grub of Oryctes nasicornis, a beetle common in Holland, but not satisfactorily ascertained to inhabit Britain, "Nothing in all nature is in my opinion a more wonderful sight than the[Pg 197] change of skin in these and other the like worms. This matter, therefore, deserves the greatest consideration, and is worthy to be called a specimen of nature's miracles; for it is not the external skin only that these worms cast, like serpents, but the throat and a part of the stomach, and even the inward surface of the great gut, change their skin at the same time. But this is not the whole of these wonders; for at the same time some hundreds of pulmonary pipes within the body of the worm cast also each its delicate and tender skin. These several skins are afterwards collected into eighteen thicker, and, as it were, compounded ropes, nine on each side of the body, which, when the skin is cast, slip gently and by degrees from within the body through the eighteen apertures or orifices of the pulmonary tubes before described, having their tops or ends directed upwards towards the head. Two other branches of the pulmonary pipes that are smaller, and have no points of respiration, cast a skin likewise." ... "If any one separates the cast little ropes or congeries of the pulmonary pipes with a fine needle, he will very distinctly see the branches and ramifications of these several pipes, and also their annular composition[479]."—Bonnet makes a similar observation with regard to caterpillars; but he appears to have observed it more particularly, at least the change of the intestines, previously to the metamorphosis of the insect, when he says with the excrements it casts the inner skin of the stomach and viscera[480]. Both these great men appear to have recorded the result of their own actual observations with regard to the proceedings of two very different[Pg 198] kinds of insects; the one the grub of a beetle, and the other the caterpillars of Lepidoptera. The account of the former is given quite in detail, as that of a person who is describing what he has actually seen: yet by a later and very able physiologist, Dr. Herold, it is affirmed that the inner skin of the intestinal canal is never cast, that canal constantly retaining its two skins. He further affirms, that they are only the large trunks of the Tracheæ that cast their skins, none being detached from their smaller ramifications[481]. When men so eminent for their anatomical skill and nicety, and for their depth and acumen, disagree, the question must be regarded as undecided till further observations throw sufficient weight into one scale or the other.

The larva which has undergone this painful process is at first extremely weak: all its parts are soft and tender; even the corneous ones, as the head and the legs, are then scarcely more than membranous, and are all bathed with a fluid, which, before the moult, intervenes between the two skins, and facilitates their separation[482]: and it is only after some hours, or in some cases even days, during which it lies without motion, that this humidity evaporates, all its parts become consolidated, and it recovers its strength sufficiently to betake itself to its wonted food. Its colour, too, is usually at first much paler than before, and its markings indistinct, until their tints have[Pg 199] been enlivened by exposure to the air, when they become more fresh, vivid, and beautiful to appearance than ever. When a few meals have invigorated its languid powers, the renovated animal makes up for its long abstinence by eating with double voracity. . A similar preparatory fast, and succeeding state of debility, accompany every change of the larva's skin. Each time except the last, the old skin is succeeded by a new one, with few exceptions, similar to the one it has discarded. Previously to the final change, which discloses the pupa, it quits the plant or tree on which it had lived, and appears to be quite unsettled, wandering about and crossing the paths and roads, as if in quest of some new dwelling. It now abstains from food for a longer time than before a common moult, empties itself copiously, and as I have just said, if Swammerdam and Bonnet are to be depended upon, casts the skin that lines the stomach and intestines, as well as that of the Tracheæ.

I have observed above, that all larvæ, with few exceptions, change their skins in the manner that I have described. These exceptions are principally found in the order Diptera, of which those of the Linnean genera Musca, Œstrus, and probably all that, like the maggot of the common flesh-fly, have membranous contractile heads, never change their skin at all, not even preparatory to their becoming pupæ. The skin of the pupa, though often differing greatly in shape from that of the larva, is the same which has covered this last from its birth, only modified in figure by the internal changes that have taken place, and to which its membranous texture readily accommodates itself. The larvæ of the Dipterous genera Tipula, Culex, and those which have corneous[Pg 200] heads, like other larvæ change their skins several times previously to becoming pupæ[483]. The grubs, also, of bees, wasps, ants? and probably many other Hymenoptera, do not change their skin till they assume the pupa, nor the larva of the female Coccus[484].

If you feel disposed to investigate the reasons of that law of the Creator which has ordained that the skins of the higher animals shall be daily, and imperceptibly, and as it were piece by piece renewed, while those of insects are cast periodically and simultaneously,—the proximate cause must be sought for in the nature of the two kinds of skin, the one being more pliable and admitting a greater degree of tension than the other, and being so constructed as to scale off more readily. If, ascending higher, you wish to know why the skins of insects are so differently circumstanced from our own, the most apparent reason is, to accommodate the skin to the very rapid growth of these animals, which a gradual and slower change would have impeded too much, or the skin have suffered constant dilapidation and injury; therefore their Beneficent Creator has furnished them with one which will stretch to a certain point, and during a certain period, and then yield to the efforts of the inclosed animal, and be thrown aside as a garment that no longer fits the wearer.

viii. And this leads me to a subject to which I am desirous[Pg 201] now to bespeak your attention,—the Growth, I mean, and size of Insects in this state. As to size, larvæ differ as much as insects in their perfect state: these last, however, never grow after their exclusion from the pupa, while larvæ increase in bulk in a proportion, and often with a rapidity, almost without a parallel in the other tribes of animals. Thus Lyonnet found, that the caterpillar of the great goat-moth (Cossus ligniperda F.) after having attained its full growth is at least 72,000 times heavier than when it was first excluded from the egg[485]; and of course had increased in size in the same proportion. Connected with the size of larvæ, is the mode in which their accretion takes place. This, with respect to the more solid parts, as the head, legs, &c., is not, as in other animals, by gradual and imperceptible degrees, but suddenly and at stated intervals. Between the assumption of a new skin and the deposition of an old one, no increase of size takes place in these parts, while the rest of the body grows and extends itself, till, becoming too big for these solid parts, nature restores the equilibrium between them by a fresh moult[486], in which the augmentation of bulk, especially in these parts, is so great, that we can scarcely credit the possibility of its being cased in so small an envelope. Malpighi declares, that the head of a silk-worm that has recently cast its skin is four times larger than before the change[487]. It is very probable, also, that when the outer skin becomes rigid, it confines the body of the larva within a smaller compass than it would expand to if unconfined, so that, when this compression is removed, the soft and elastic new integument[Pg 202] immediately swells out, and the animal appears all at once much larger than it was before the moult. In fact, the proximate cause of the rupture and rejection of the old skin is the expansion of the included body, which at length becomes so distended as to split its envelope, aided, indeed, as before described, by the contortions of the creature itself.

The larvæ most notorious for the rapidity of their growth are those of Musca carnaria and other flesh-flies: some of which Redi found to become from 140 to more than 200 times heavier in twenty-four hours[488]: an increase of weight and size in so short a time truly prodigious, but essential for the end of their creation—the rapid removal of dead and putrescent animal matter. As the skins of these larvæ are never changed, we may conclude, if the cause of the change of skin in other larvæ above surmised be accurate, that their skins are more contractile and capable of a greater degree of tension than those of larvæ that are subject to moulting. And two peculiarities observable in them confirm this idea: in the first place, their head is not hard and corneous, as that of the others, but capable of being shortened or lengthened; and in the next, their breathing-pores are not in the sides, but at the extremities of the body, while in the moulting larvæ there are two in almost every segment, which must form so many callous points that impede the stretching of the skin to the utmost. The hairs, spines, and tubercles, that are so often found on caterpillars, must also form so many points of resistance that prevent that full extension of the integument which it might otherwise admit.

[Pg 203]

There is not always that proportion between the size of larvæ and of the insects that proceed from them that might have been supposed, some small larvæ often producing perfect insects larger than some of those proceeding from such as are of greater size.

ix. As insects often live longest in the state we are treating of, I shall say something next upon the age of larvæ, or the period intervening between their exclusion from the egg and their becoming pupæ. This is exceedingly various, but in every case nicely adapted to their several functions and modes of life. The grubs of the flesh-fly have attained their full growth, and are ready to become pupæ, in six or seven days; the caterpillar of Argynnis Paphia, a butterfly, in fourteen days; the larvæ of bees in twenty days; while those of the great goat-moth (Cossus ligniperda) and of the cockchafer (Melolontha vulgaris) live three years, or at least survive three winters, before the same change. That of another lamellicorn beetle (Oryctes nasicornis F.) is said to be extended to four or five; that of the wire-worm (Elater segetum) to five. That of the stag-beetle (Lucanus Cervus) is affirmed by Rösel to be extended to six years; but the most remarkable instance of insect longevity is recorded by Mr. Marsham in the Linnean Transactions[489]. A specimen of Buprestis splendida, a beautiful beetle never before found in this country, made its way out of a deal desk in an office in London in the beginning of the year 1810, which had been fixed there in the year 1788 or 1789; so that according to every appearance it had existed in this desk[Pg 204] more than twenty years. Ample allowance being made for its life as a pupa, we may conclude that it had existed as a larva at least half the above period. The grubs of the species of the genus Cynips L. attain their full size in a short time; but they afterwards remain five or six months in the gall before they become pupæ[490].

With few exceptions it may be laid down, that those larvæ which live on dead animals, in fungi, in dung, and in similar substances, are of the shortest duration in this state; and that those which live under the earth, on the roots of grass, &c. and in wood, the longest: the former becoming pupæ in a few days or weeks, the latter requiring several months, or even years, to bring them to maturity. The larvæ which live on the leaves of plants seem to attain a middle term between the one and the other,—seldom shorter than a few weeks, and rarely longer than seven or eight months. Aquatic larvæ appear to be subject to no general rule: some, as the larvæ of Gnats, becoming pupæ in two or three weeks; and others, as those of the Ephemeræ, which are thus compensated for their short life as flies, in as many years[491]. The cause of all these differences is obviously dependent on the nature of the food, and the purposes in the economy of creation to which the larvæ are destined.

x. The last part of the history of larvæ relates to their Preparations for assuming the pupa state. When they have acquired their full size, after having ceased to take[Pg 205] food, by a copious evacuation they empty the intestinal canal, even rejecting the membrane that lines it and the stomach[492]; their colours either change totally, or fade; and they make themselves ready for entering upon a new stage of their existence. Some merely rest in a state of inactivity in the midst of the substances in which they feed, as if conscious of their inability to select any safer abode. Of this description are most Coleopterous, Hymenopterous, and Dipterous larvæ, that feed under ground, or in the interior of trees, fruits, and seeds.

But a still larger tribe, those which feed on leaves, animals, &c. act as if more sensible of the insecurity of this to them important epoch. They are about to exchange their state of vigour and activity for a long period of deathlike sleep. The vigilant caution which was wont to guard them from the attack of their enemies will be henceforward of no avail. Destitute of all the means of active defence, their only chance of safety during their often protracted night of torpor must arise from the privacy of their place of repose. About this, therefore, they exhibit the greatest anxiety. Many, after wandering about as if[Pg 206] bewildered, retire to any small hole on the surface of the earth, covering themselves with dead leaves, moss, or the like, or to the chinks of trees, or niches in walls and other buildings, or similar hiding-places. Many penetrate to the depth of several inches under ground, and there form an appropriate cavern by pushing away the surrounding earth; to which they often give consistence by wetting it with a viscid fluid poured from the mouth. The larvæ of other insects undertake long and arduous journeys in search of appropriate places of shelter. Those of flesh-flies, now satiated with the mass of putridity in which they have wallowed, leave it, and conceal themselves in any adjoining heap of dust. The grubs of the gad-fly (Œstrus) creep some of them out of the backs of cattle, in tumours of which they have resided, and suffer themselves to fall to the earth; while others, which have fed in the stomach of horses, quit their hold, and by a still more extraordinary and perilous route are carried through the intestines the whole length of their numerous circumvolutions, and are discharged at the anus. And without enumerating other instances, various aquatic larvæ, as that of a common fly (Elophilus pendulus), &c. leave the water, now no longer their proper element, and betake themselves to the shore, there to undergo their metamorphosis.

Most of these, having reached their selected retreat, require no other precaution; but another large tribe of larvæ have recourse to further manœuvres for their defence before they assume the pupa. Those of the aphidivorous flies (Syrphus F. &c.), of the various lady-birds (Coccinella L.), and tortoise-beetles (Cassida L.), &c. fix themselves by the anus with a gummy substance to the[Pg 207] leaves or twigs under which they propose to conceal themselves during their existence in that state. Others previously suspend themselves by a silken thread fixed to the tail, or passing round the body; by which also, when become pupæ, they are afterwards pendent in a similar position; and lastly, a very great number of larvæ wholly inclose themselves in cases or cocoons, composed of silk and various other materials, by which during their state of repose they are protected both from their enemies and the action of the atmosphere. As these two last-mentioned processes are extremely curious and interesting, I shall not fear tiring you by entering into some further detail respecting them: explaining first the mode by which larvæ suspend themselves, both before and after they are become pupæ, by silken threads; and next, the various cases or cocoons in which others inclose themselves, and their manner of operating in the formation of them.

1. The larvæ which suspend themselves and their pupæ, with the exception of the tribe of Alucitæ, and some Geometræ of the family of G. pendularia, punctaria, &c. are almost all butterflies[493]. No others follow this mode. They may be divided into two great classes—those which suspend themselves perpendicularly by the tail, and those which suspend themselves horizontally by means of a[Pg 208] thread girthed round their middle. In both cases it should be observed, that the suspension of the pupa is the object in view; but as the process is the work of the larva, this seems the proper place for explaining it. To begin with the first case.

You are aware that all lepidopterous larvæ have the faculty of spinning silk threads from their mouths, and it will readily occur to you that it is by means of these threads that they suspend themselves. But how? How is a caterpillar to hang itself by the tail to threads spun from the mouth? Even suppose this difficulty overcome, others still greater remain. Suppose the caterpillar to be suspended by its tail,—this is but a preparatory operation,—what is required is, that the pupa shall hang in the same position: now when you take into consideration that it is incased within the skin of the larva, and without feet or other external organs; that it has to extricate itself from this skin; to hang itself in its place, and to detach the skin from the threads which hold it—this will appear no trifling task. Indeed at first view it seems impossible. Country-fellows for a prize sometimes amuse the assembled inhabitants of a village by running races in sacks: take one of the most active and adroit of these, bind him hand and foot, suspend him by the bottom of his sack with his head downwards, to the branch of a lofty tree; make an opening in one side of the sack, and set him to extricate himself from it, to detach it from its hold, and suspend himself by his feet in its place. Though endowed with the suppleness of an Indian juggler, and promised his sack full of gold for a reward, you would set him an absolute impossibility: yet this is what[Pg 209] our caterpillars, instructed by a beneficent Creator, easily perform. Their manœuvres I shall now endeavour to explain.

When the caterpillar has selected the under-side of the leaf or other object to which it purposes suspending itself, its first process is to spin upon it a little hillock of silk consisting of numerous loosely interwoven threads; it then bends its body so as to insinuate the anal pair of prolegs amongst these threads, in which, by a slight exertion, the little crochets which surround them[494] become so strongly entangled as to support its weight with ease. It now suffers the anterior part of the body to fall down, and it hangs perpendicularly from its silken support with its head downwards. In this position it remains often for twenty-four hours, at intervals alternately contracting and dilating itself. At length the skin is seen to split on the back near the head, and a portion of the pupa appears, which by repeated swellings acts like a wedge, and rapidly extends the slit towards the tail. By the continuance of these alternate contractions and dilatations of the conical pupa, the skin of the caterpillar is at last collected in folds near the tail, like a stocking which we roll upon the ancle before withdrawing it from the foot. But now comes the important operation. The pupa, being much shorter than the caterpillar, is as yet at some distance from the silken hillock on which it is to be fastened; it is supported merely by the unsplit terminal portion of the latter's skin. How shall it disengage itself from this remnant of its case, and be suspended in the air while it climbs up to take its place? Without arms or legs to[Pg 210] support itself, the anxious spectator expects to see it fall to the earth. His fears, however, are vain; the supple segments of the pupa's abdomen serve in the place of arms. Between two of these, as with a pair of pincers, it seizes on a portion of the skin; and bending its body once more, entirely extricates its tail from it. It is now wholly out of the skin, against one side of which it is supported, but yet at some distance from the leaf. The next step it must take is to climb up to the required height. For this purpose it repeats the same ingenious manœuvre, making its cast-off skin serve as a sort of ladder, it successively with different segments seizes a higher and a higher portion, until in the end it reaches the summit, where with its tail it feels for the silken threads that are to support it. But how can the tail be fastened to them? you ask. This difficulty has been provided against by Creative Wisdom. The tail of the pupa is furnished with numerous little hooks pointing in different directions[495], as well adapted to the end in view as the crochets of the larva's prolegs, and some of these hooks are sure to fasten themselves upon the silk the moment the tail is thrust amongst it. Our pupa has now nearly completed its labours; it has withdrawn its tail from the slough, climbed up it, and suspended itself to the silken hillock—manœuvres so delicate and perilous, that we cannot but admire that an insect which executes them but once in its life, should execute them so well: nor could it, as Reaumur has well and piously observed, had it not been instructed by a Great Master. One more exertion remains: it seems to have as great an antipathy to its cast-off skin,[Pg 211] as one of us should, when newly clothed after a long imprisonment, to the filthy prison garments we had put off. It will not suffer this memento of its former state to remain near it, and is no sooner suspended in security than it endeavours to make it fall. For this end—it seizes, as it were with its tail, the threads to which the skin is fastened, and then very rapidly whirls itself round, often not fewer than twenty times. By this manœuvre it generally succeeds in breaking them, and the skin falls down. Sometimes, however, the first attempt fails: in that case, after a moment's rest, it makes a second, twirling itself in an opposite direction; and this is rarely unsuccessful. Yet now and then it is forced to repeat its whirling, not less than four or five times: and Reaumur has seen instances where the feet of the skin were so firmly hooked, that after many fruitless efforts the pupa, as if in despair, gave up the task and suffered it to remain[496]. After these exertions, it hangs the remainder of its existence in this state until the butterfly is disclosed.

We are now to consider the second mode of suspension, in which larvæ by means of a silken girth round their middle, fix themselves horizontally under leaves, &c. These follow the same process with that of those last described, in spinning a small hillock of silk to which they fasten their hind legs; and if the operation concerned the larva state alone, this would be sufficient, as by means of this support, and of their prolegs, they could easily retain themselves in a horizontal position. But these larvæ[Pg 212] act as if they foresaw the assumption of a state in which they will be deprived of legs. It is the suspension of the forthcoming pupa that is the object in view; and though this can be hung by the tail in the same way with those of the first class, yet it is plain that it cannot be retained in a horizontal position, which for some unknown reason is essential to it, without some support to its anterior extremity. It is necessary for the larva, therefore, not only to fix its posterior legs amongst a collection of silken fibres, but to spin a girth of the same material round its body. This girth, though apparently of a single thread, will be found on examination to be composed of several, often as many as fifty or sixty; and is fastened on each side of the body of the larva about the middle, to the surface under which it is placed. Three different modes of fixing these girths are adopted by the caterpillars of different butterflies. Some, as those of the common cabbage-butterfly (Pieris Brassicæ), which have remarkably pliable bodies, bend them almost double on one side, then fix the thread and carry it over to the other in the same position, repeating this operation as often as is necessary. Others, as that of Lycæna Argus and many more of the Papiliones Rurales and Urbicolæ L., which have a short and more rigid body, after having bent the head on one side so as to fix one end of the thread, bring themselves into a straight position, and, by a manœuvre not easily described, contrive to introduce the head under the thread, which they then bend themselves to fasten on the other side, pushing it to its proper situation by the successive tension and contraction of their segments. But the most curious mode, though indeed that which seems most natural, is adopted[Pg 213] by the caterpillar of the beautiful swallow-tail butterfly (Papilio Machaon) and others of the same family. This first forms the loop which is to serve for its girth, and then creeps under it. But the difficulty it has to surmount is, to keep itself from being entangled in the fifty or sixty fine distinct threads of which the girth is composed, and to preserve them all extended so as to be able to introduce its body beneath them. For this purpose it makes use of the two first pair of its fore-legs, employing them as a woman does her hands in winding a skein of cotton, to collect and keep all the threads of its card unentangled and properly stretched; and it is often with great difficulty, towards the end of the process, that it prevents them from slipping off. When a sufficient number of threads is completed, the animal bends its head between its legs, and insinuates it under the collected loop, which by its annular contraction it easily pushes to the middle of the body.

In about thirty hours after the larvæ which girth themselves have finished their operations, the skin splits, and the pupa disengages itself from it by those contractions and dilatations of its segments which have been before described, pushing the exuviæ in folds to the tail, by different motions of which it generally succeeds in detaching them. One would have thought there would be considerable difficulty in slipping the skin past the girth; but this, according to Reaumur, seems to be easily effected[497].

If you are desirous of witnessing for yourself the manœuvres by which these curious modes of suspension are[Pg 214] effected, you may be readily gratified. It is only necessary to collect and feed until their metamorphosis the black spinous caterpillars of the common peacock-butterfly (Vanessa Io), which in most places may be found upon nettles, or those of the Pieris Brassicæ, which swarm in cabbages or brocoli in every garden. The former will exhibit to you a specimen of vertical, the latter of horizontal suspension. It should be observed, however, that to hit the precise moment when these processes are going on, it is necessary to feed a considerable number of the larvæ of each kind; some one of which, if you watch them narrowly when they have attained their full growth, you will scarcely fail to surprise in the act.

I must observe here, that although the vertical and horizontal are the two principal positions in which caterpillars suspend themselves, yet that others are inclined at various angles; and some are attached with less art, appearing only to be fastened by some part of their abdomen to the body upon which they are fixed[498].

2. The larvæ whose procedures I am in the next place to describe, are those which, previously to assuming the pupa state, inclose themselves in cases or cocoons of different materials. For the sake of method, I shall divide these into two great classes: First, those which form their cocoons entirely or principally of silk; and secondly, those which form them chiefly of other substances.

To begin with the first. The larvæ which inclose themselves in silken cocoons are chiefly of the Lepidopterous tribes of Bombycidæ and Noctuidæ; but a few[Pg 215] Geometræ (G. papilioniaria, lactearia, &c.); most of the Hymenoptera; some Coleoptera, as certain of the weevil tribe (Hypera Arator, Rumicis Germ.), and those brilliant beetles frequenting aquatic plants constituting the genus Donacia F.; the Neuropterous genera Hemerobius and Myrmeleon; Mycetophila and a few others in the Diptera; and Pulex in the Aphaniptera fabricate coverings of the same material. In all, with the exception of Myrmeleon and Hemerobius (and perhaps Hypera Rumicis, &c.?) which have their spinning apparatus at the extremity of the abdomen, the silken thread employed in forming these coverings proceeds from the middle part of the under-lip, as before explained; and is in fact composed of two threads gummed together as they issue from the two adjoining orifices of the spinner.

Of the larvæ which inclose themselves in silk, the most familiarly known is the silk-worm: the cocoon of this consists exteriorly of a thin, transparent, gauze-like coating, through the interstices of which can be seen an inner, smaller, oval ball of a more close and compact texture. The whole is in fact composed of one single thread, but arranged in two distinct modes. To form the exterior envelope, which is merely the scaffolding by means of which the inner and more solid covering is constructed, the caterpillar, after fixing upon a space between two leaves or twigs or angles suitable for its purpose, begins by glueing one end of its thread to one of the adjoining surfaces. This thread it next conducts to another part and then fastens, repeating this process and interlacing it in various directions, until it has surrounded itself with a slight and loosely spun netting. In the centre of this, when contracted into a space sufficiently small,[Pg 216] it lays the foundation of the interior cocoon. Fixing itself by its prolegs to some of the surrounding threads, it bends its body, and by successive motions of its head from side to side spins a layer of silk on the side opposite to it: when this is of the requisite thickness, the larva shifts its position, and repeats the same process in another quarter, covering each layer in turn with a new one until the interior cavity is reduced to the size desired. Thus, the silken thread which forms this new cocoon is not, as might have been supposed, wound circularly as we wind the thread of a ball of cotton; but backwards and forwards in a series of zigzags, so as to compose a number of distinct layers. Malpighi could distinguish six of these layers[499], and Reaumur suspects there is often a greater number[500]. The former found the length of the thread of silk composing them when wound off, without including the exterior case, to be not less than 930 feet[501]; but others have computed it at more than a thousand[502]: consequently the threads of five cocoons united would be a mile in length. Estimating by the weight,—the thread of a pound of cocoons, each of which weighs about two grains and a half, would extend more than 600 miles[503], and such is its tenuity, that the threads of five or six cocoons require to be joined to form one of the thickness requisite in the silk manufacture. It is the continuous thread of the inner cocoon which is most valuable; the outer loose coating from its irregularity cannot be[Pg 217] wound off, and is known in commerce by the name of floss silk.

Manœuvres in their general principle similar to those of the silk-worm are followed by most of those larvæ which inclose themselves in silken cocoons. Many species, however, adopt variations in the mode of procedure all of which it would be tedious to particularize, but some of them are worth mentioning. The larvæ of Tortrix prasinana, and other species of moths which form cocoons resembling a reversed boat, arrange their threads in layers, so as to construct two parallel walls gradually inclining towards the top and ends, where they finally force them to approach each other by means of an apparatus of silken cables[504]. And the larva of Saturnia Pavonia, though it forms the base of its flask-shaped cocoon by spinning like the silk-worm a number of interwoven zigzags, places the threads which compose the interior funnel-like opening of the apex nearly straight, parallel to each other, and converging towards the same point in the centre[505].

These last, as well as almost all larvæ, constantly remain in the inside of the cocoon during its construction. But De Geer has given us the history of a minute caterpillar of a species of moth (Tinea L.) which feeds on the under side of the leaves of the Rhamnus Frangula, or Black Alder, that actually weaves half of its cocoon on the outside. This cocoon, which is very small, is beautifully fluted, consisting of several longitudinal cords, with the intervals filled by fine net-work, and shaped like a reversed boat[506]. The animal begins by laying the foundations[Pg 218] of one of the ends of her cocoon, she adds new threads to this small beginning, and so proceeds. As the work advances she retreats backwards, and her body is situated nearly in the same line with the cocoon she has begun, and quite out of it; she only touches with her head and legs its anterior margin. When half the cocoon, or rather of its exterior layer, is finished, she suspends her operations for some moments. She then for the first time introduces her head into this demi-cocoon, and turns herself in it by doubling her supple body, and passing one part over the other, so that at last she manages to bring her tail into the pointed end of the cocoon, the head and the anterior half of her body remaining without. Thus situated, she commences her operations afresh. At a distance from the margin of the demi-cocoon, equal to its length, she begins to spin the pointed end of the other moiety, the length of her body serving her as a measure that enables her to begin at the proper distance from it. This new portion she spins in the same manner as the other; but as she is prevented by the demi-cocoon in which the posterior part of her body is lodged from retreating backwards, she contracts her body more, which answers the same purpose. When the new work is so advanced that she can no longer contract her body, she bends the anterior part of it considerably, and reverses her head. When the distance between the margin of the two halves of the cocoon is very small, so as no longer to admit the head between them, in order to unite them she is obliged to have recourse to another manœuvre. Withdrawing her head, she extends silken longitudinal threads between the two margins, and thus unites them. This part is more clumsy, and not so regular as[Pg 219] the rest of the cocoon, so that the point of union is always discoverable. These caterpillars do not always divide the cocoon into two equal portions, for often they will finish three quarters of the cocoon before they enter it, and begin at the other end[507].

The general rule is,—that each larva spins for itself a separate cocoon; but amongst those of Arctia chrysorhea and others which live in society, two or three sometimes begin their operations so close together that they are under the necessity of forming one common cocoon, which serves for a covering to the whole number. The same thing happens to silk-worms, the double or treble cocoons of which are called Dupions by the breeders. The larvæ of some Ichneumons, besides forming each its separate cocoon, spin a joint cottony covering for the whole[508], which is effected thus:—After they leave the caterpillar they have devoured, they fix themselves side by side at a little distance from it, and begin to spin each a cocoon; and in order to defend its end and side that is not covered by others, they spin further an envelope of loose silk, and thus this exterior covering is formed.

The size, figure, colour, substance, and texture of silken cocoons are extremely various. Their size indeed is usually proportioned to that of the included larva or pupa; yet it is by no means always so. Some large caterpillars spin cocoons so small, that the observer can hardly conceive how they can be contained in so narrow a compass: Eriogaster Catax is a moth of this description[509]. And others smaller in size lodge themselves in[Pg 220] apartments apparently much more spacious than necessary. The transparent hammock-like cocoons of Hepialus Humuli and Arctia villica, two other moths, would contain several of their pupæ. I possess one in which the pupa is suspended in the centre, that is ten times its size, and not very short in dimensions of that of Attacus Paphia, a giant silk-moth. The largest cocoon I ever read or heard of, is that thus described by Mr. Hobhouse in his Travels: "Depending," says he, "from the boughs of the pines, near the Attic mountain Parnes, and stretching across from tree to tree so as to obstruct our passage, were the pods, thrice as big as a turkey's egg! and the thick webs of a chrysalis, whose moth must be far larger than any of those in our country."[510] If this statement is correct, and I am not aware that there is any reason for doubting it, the cocoon must be vastly larger than the pupa, or the moth it produced would far exceed in size any yet known. Perhaps, however, as this gentleman is probably no entomologist, what he took for a cocoon might be a nidus, in which many larvæ were associated, of the nature of those formerly described[511].

With regard to figure, the majority are like those of the silk-worm, of a shape more or less oval or elliptic: some, however, vary from this. That of Lasiocampa Rubi is oblong. I have one from New Holland somewhat resembling an acorn, fixed to the twigs of some tree or shrub, of a very close silk, and covered by a circular operculum, which the animal pushes off when it assumes the imago; this is ovate or conico-ovate; others again are globose[512]; others are conical[513], as that of Gastropacha[Pg 221] quercifolia; others almost fusiform[514] (Odenesis potatoria). Reaumur received one from Arabia which was nearly cylindrical[515]. Those of T. prasinana before noticed, and many other Tortrices, are shaped like a reversed boat[516]; that of Saturnia Pavonia and others of the same tribe, like a Florence flask with a wide and short neck. The cocoon of Lygæna Filipendulæ resembles a grain of barley. Another cocoon in my cabinet, of very slight network, is shaped something like an air-balloon. But the most remarkable one for its form and characters, is one that I received from the rich cabinet above quoted. This, which is of an unusually close texture, is suspended by a thread more than two inches long from the point of a leaf; it then swells into a perfect cone, at the base about four-fifths of an inch in diameter and half an inch in length, and covered with scattered setiform appendages: from the centre of the base projects a large hemispherical protuberance, which terminates in a long stalk, much thicker than the thread that suspends the cocoon. There is commonly no difference between the shape of cocoons spun by larvæ which are to give birth to different sexes of the same species. The silk-worm cocoons, however, which will produce male moths, have more silk at the ends, and consequently are more round than those which are to produce females: but the difference is not striking.

The most usual colour of silken cocoons is white, yellow, or brown, or the intermediate shades. The whites are very pure in the general envelope of some species of Ichneumonidæ, and yellows often very brilliant. But[Pg 222] besides these more general colours, some cocoons are black[517], some few blue or green, and others red[518]. Sometimes the same cocoon is of two different colours. Those of certain parasites of the tribe of Ichneumones minuti L. the motions of one of which I noticed on a former occasion[519], are alternately banded with black or brown and white, or have only a pale or white belt in the middle, which gives them a singular appearance. In both cases the difference in colour depends upon the different tints with which the silky gum is imbued in the reservoirs: the first portion of it is white, and with this the larva first sketches the outline of its cocoon, and then thickens the layers of silk considerably in those parts where the white bands appear: when these are finished, its stock of white silk is exhausted, and the remainder of the interior of the cocoon is composed of brown silk[520]. The circular operculum above mentioned as covering an acorn-shaped cocoon, is paler than the latter, and also ornamented by a zone within the margin of deep brown. The pale cocoon also of Attacus Paphia is veined with silk of a deep red.

I have very little to say on the substance of the silk of cocoons. Though that of the silk-worm is composed of such a slender thread, that of many others is still finer, scarcely yielding in tenuity to the spider's web. On the other hand, the silk of the cocoons of Saturnia Pavonia and of several foreign species is as thick as a hair.

With regard to the texture of their cocoons—in some, as in that of the silk-worm, the threads are so slightly[Pg 223] glued to each other, as to separate with facility; but in that of the emperor-moth just mentioned they are intimately connected by a gummy matter, furnished, as Reaumur conjectures, from the anus[521], with which the whole interior of the cocoon is often plastered. Some, as that of the silk-worm, are composed of an exterior loose envelope, and an inner compact ball; others have no exterior covering, the whole cocoon being of an uniform and thick texture. The larva of Cossus Robiniæ Peck, in spinning its cocoon, makes the end next the opening to the air, by which the imago is to emerge, of a slighter texture than the rest of it[522]. The exterior case is sometimes, as in Laria pudibunda, very closely woven, so as to resemble a real cocoon[523]: its form is usually adapted to that of the inner one; but in some which fix them under flat surfaces (Laria fascelina, Callimorpha Caja,) it resembles a hammock[524]. Cocoons of a close texture have generally no orifice in any part; but that of Eriogaster lanestris is spun with openings, as if bored from without, the use of which, however, does not seem to have been ascertained[525].

Many silken cocoons are of so close a fabric, as, when finished, entirely to conceal the included insect; but a very considerable number are of a more open texture, composed of a much smaller quantity of silk, and that woven so loosely, that the larva or pupa may always be discovered through it. Of this description are the cocoons of Hypogymna dispar, Arctia Salicis, &c., which consist only of a few slight meshes. Those of some others[Pg 224] resemble gauze or lace[526]. Of the first description is one in my cabinet before alluded to, shaped somewhat like an air-balloon; the meshes are large and perfectly square. The pupa hangs in the centre, fixed by some few slight threads which diverge from it to all parts of the cocoon—so that it looks as if it was suspended in the air, like Mahomet's coffin, without support. Of the second description is a black one with very fine and nearly circular meshes: the threads that form these are thick, and seem to be agglutinated. In our own country, the cocoons of some beetles, as of Hypera Arator, Galeruca Tanaceti, and of some little Tineæ, also resemble gauze. Many of the larvæ, however, which spin these cocoons, whose thinness is probably attributable to the smallness of their stock of silk, seem anxious for a more complete concealment; and therefore commonly either hide them between leaves tied together, in some with a certain regularity, in others without art[527]; or thicken their texture, and render it opaque, by the addition of grains of earth[528], or of other materials with which their bodies supply them. These are principally of two kinds. The larvæ of Lasiocampa Neustria, Arctia Salicis, &c. after spinning their cocoons, cast from their anus three or four masses of a soft and paste-like matter, which they apply with their head all round the inside of the cavity; and which, drying in a short time, becomes a powder that effectually renders it opake. This is not, as might be conjectured, an excrement, but a true secretion, evidently[Pg 225] intended for this very purpose: and, according to Reaumur, a similar powder, but white, derived from the varicose intestines, is used by the caterpillars of Gastropacha quercifolia, &c.[529] The other material, which is still more frequently employed, and which is occasionally mixed with the former, is the hair which everyone has observed to cover so thickly the bodies of some caterpillars. This, after spinning a sufficient envelope, they tear, or in some instances cut off with their mandibles, and distribute all round them, pushing it with their head amongst the interstices of the silk, so as to make the whole of a regular thick texture. After this process, which leaves the body completely denuded, and often seems to give them great pain, they conclude by spinning another tissue of slight silk, in order to protect the forthcoming pupa from the surrounding prickly points. It should be observed, however, that though many hairy larvæ, as those of Noctua Aceris, Arctia Caja, and others, employ their hairs in the composition of their cocoons, the rule is not general, several never making any such use of them. Nor do all that do so employ them distribute them in the same manner as those above described, which rarely attempt to arrange them in any regular position. Reaumur has noticed a small hairy caterpillar that feeds on lichens, which is more methodical: this actually places its hairs upright, side by side, as regularly as the pales in a palisade, in an oval ring around its body, connecting them by a slight tissue of silk, which forces them to bend into a sort of roof at the top; and under this curiously-formed cocoon assumes its state of pupa[530]. Some larvæ make so much[Pg 226] hair and so little silk enter into the composition of their cocoons, that on the first inspection they would be pronounced wholly composed of it[531]; others, thickening the interior of their cocoon with hair, line the whole with a viscid matter like varnish[532].

The larvæ of some saw-flies (Tenthredo L.) are remarkable for inclosing themselves in a double cocoon, in which the inner is not, as in the silk-worm &c., connected with the outer, but perfectly distinct from it. Some species, as T. Rosæ (Cryptus Jur.), which have but a small stock of silk, compose the outer cocoon of thick silken cords crossing at right angles, and forming an oval net; which at the same time that it protects them effectually from the ants, which are always ready to attack them, demands much less silk than a covering of a closer texture. But the tender nymph itself requires to be inclosed in a case of a softer and more delicate substance; and accordingly the inner cocoon is composed of fine silk, woven so closely that the threads are scarcely perceptible under a microscope[533]. Reaumur mentions a hymenopterous larva belonging to Latreille's Fossores (Sphex L.) which thickened its cocoon with the legs, wings, and other relics of the flies which it had devoured[534]: trophies—like the drinking-cups of some savages, made of the skulls of their enemies, or the skull pyramid near Ispahan—of its powers of devastation.

It is a general rule, that those larvæ which spin cocoons, never in ordinary circumstances become pupæ without having thus inclosed themselves. An exception, however, is met with in the larva of a species of ant noticed[Pg 227] by De Geer (Formica fusca L.), some of the individuals of which inclose themselves in cocoons; while others neglect this precaution, and undergo their metamorphosis uncovered[535]. Rösel also made nearly the same observation on the larva of the flea[536].

I must say something with regard to the situation, often very remote from their place of feeding, in which larvæ fabricate their cocoons. A very considerable number, probably the majority, form them either partially (Arctia lubricipeda) or wholly under ground; others beneath dead leaves, moss, or in the chinks of the trees; others within the wood in substances on which they have fed; the larva of Cossus leaves in these a communication with the open air by which the imago emerges; and a large number attach them to the leaves and branches of trees and plants; the cocoon of Donacia fasciata(?) is fastened by one side to the roots or surculi of Typha latifolia. There is usually nothing very remarkable in the mode of fixing them, the exterior threads being merely gummed irregularly to different portions of the objects which support them. But some effect this with greater art. I have one from New Holland, very long, which is suspended from a twig by a long riband, as it were, which entirely girths the twig. The larva of the magnificent silk-moth, Attacus Paphia, actually forms a solid silken stalk to its cocoon, an inch and half in length[Pg 228] and a line in diameter, fastened by the other extremity to a twig, which it closely surrounds as if with a ring, at first sight resembling a fruit of a very singular appearance[537]. I have specimens of this cocoon with both stalk and ring. A bell-shaped cocoon fastened by a foot-stalk, but of softer consistence, to a blade of grass, found by Mr. Sheppard, I can also show you; and my friend Mr. Wilkin had a similar one out of the late Mr. Hudson's collection. Most larvæ spin their cocoons in solitude: some of those, however, which live in society do it close together under their common tent.

There are other cocoons that should be noticed here, such as those formed by the larva of Zygæna Filipendulæ, and some Bombyces, saw-flies (Tenthredo L.), and beetles (Curculio, Donacia F.), &c. These are formed of a substance which seems more analogous to gum than silk, yet furnished from the silk reservoirs, and usually present the appearance externally of parchment or membrane. That of the insect first mentioned is coated, however, with a slight interior silken lining; as indeed are almost all cocoons, of whatever substance.

The second class, into which I have divided larvæ that inclose themselves in cocoons, includes those which form their coverings not solely or principally of silk, but in which other materials are mixed more or less. The cocoons of some of these larvæ are merely composed of a few leaves slightly tied together, either irregularly, or arranged, particularly when they are of a linear figure, with considerable symmetry. The grubs of many beetles, as of[Pg 229] the rose-beetle, Cetonia aurata, &c., prepare themselves a cocoon, composed of earth, pieces of rotten wood, and any substances within their reach: which they fasten together with a glutinous secretion. The same material is employed by others in forming a cocoon wholly of earth; which is sometimes, as that of the stag-beetle, Lucanus Cervus, exceedingly hard; at others, as that of some moths, Noctua ambigua, &c., so slight as to fall to pieces as soon as touched[538]. Other cocoons are formed of grains of earth. Reaumur has given a very interesting account of the procedures of a larva in repairing one of these cocoons, from which he had broken off the top when just completed. Without quitting the interior of the walls that remained, it put out its head from the breach, and for more than an hour employed itself in selecting one by one grains of earth, which it conveyed with its mandibles and deposited within its case: it next spun all round the opening threads of silk, to which it attached grains of earth taken from the previously-stored heap, uniting them compactly by means of other silken threads. After employing three hours in this laborious process, the industrious little mason had reduced the diameter of the breach to a few lines. Reaumur was very curious to know how it would fill up this orifice, which would no longer admit the protrusion of its head outside the walls, as in its previous operations. He concluded, that while the rest of the cocoon was exteriorly formed of earth, this opening would be merely closed with silk. He was mistaken, however: the artist knew how to vary its[Pg 230] manœuvres, and make its vault of one uniform texture. It spun across the opening a little net of silk, between the meshes of which it thrust grains of earth so dexterously that they projected as far as the outer surface, retained there probably by silken lines previously attached and fastened within. It then finished its habitation by fortifying the inside of the orifice with another layer of earth[539]. The ant-lion (Myrmeleon) spins a globular cocoon with its anus, which it covers with grains of sand[540]. One that I took in the forest of Fontainebleau, in the quarry that produces the crystallized sandstone called the Fontainebleau fossil, was covered with large and shining grains. Instead of the grains of earth or sand employed by these larvæ, those of another tribe substitute grains of stone detached from the softer walls, upon whose lichens they previously feed, which they unite into solid oval cocoons[541]. Those of a fourth form their cocoons of patches of short moss arranged with the roots downwards, and forming a vault, as it were, of verdant turf, admirably adapted for concealment[542]. The larvæ of some moths form their cocoons of irregular pieces of bark tied together with silk, and resembling when completed a knotty protuberance of the twig on which they are fixed. That of Pyralis tuberculana constructs a pannier-shaped one of the parenchyma of the leaves of plants[543].

All these cocoons, however, must yield in point of singularity of construction, materials, and ingenuity, to one formed by a small caterpillar, described by the illustrious naturalist lately quoted, which feeds upon the oak. This cocoon is wholly composed of small rectangular[Pg 231] strap-shaped pieces of the fine upper skin, or epidermis of the twig upon which it rests, regularly fastened to each other in a longitudinal direction with very slender silken cords. But the mode of its construction is even more remarkable than the substance of which it is fabricated. The caterpillar's first process is to form its slips of bark into two flat triangular wing-like pieces, projecting opposite to each other from each side of the twig, somewhat like the feathers of an arrow. It does not, perhaps, require any great degree of intelligence in a larva to give its cocoon the usual oval form, when it begins to arrange its materials in that shape from the very first, and round so good a mould as its own bent body; but we surely must admit that it is a task to which no stupid artist would be competent, to form first a multitude of strap-shaped laminæ into two triangular plates, and then to bend these plates into a case resembling the longitudinal section of a cone, with an elliptical and protuberant base,—the figure which the cocoon of this insect assumes. All the minutiæ of the manœuvres which it employs in this nice operation could not be comprehended without a more diffuse explanation than I have here room to give: suffice it to say, that the caterpillar fastens silken lines to each exterior opposite and longer side of the laminæ, and by applying all the weight of its body forces them to bend and approach each other, in which position it secures them by other shorter lines. It next repeats the same process with the upper and shorter sides of the plates; which when joined form the base of the cocoon. Both these tasks are accomplished in less than an hour, and the seams are so nicely joined as to be imperceptible. A fine inner tapestry of silk, covering all the asperities of the exterior[Pg 232] walls, concludes its labours[544]. It is to be lamented that Reaumur was unacquainted with the moth that proceeds from the pupæ inclosed in these ingenious cocoons; which being small, and precisely of the same colour as the bark of the twig that supports them, are not to be discovered but by a very narrow inspection. It would seem, however, to be Noctua Strigula of Berkhausen, Pyralis strigulalis of Hubner[545]. The larva, he informs us, is found in May: its body is flatter than common, of a yellowish flesh-colour, clothed with tufts of red hair on each segment, and furnished with fourteen feet. Should this description enable you to detect it upon your oaks, a view of its ingenious procedures would amply repay you for the trouble of seeking for it. The larvæ of Cerura vinula, Stauropus Fagi, and several other moths, form their cocoons of grains of wood gnawed from the trees on which they feed. These grains they masticate, mixed with a glutinous fluid secreted from the mouth, into a paste, which forms a covering of an uniform smooth texture, and so hard as not readily to yield to a knife. Of a substance apparently nearly similar is composed the cocoon of a weevil related to Liparus Pini; which with its inhabitant was given me by the ingenious Mr. Bullock. A little moth, whose ravages have been before noticed[546], lines the interior of the grain of barley, of which it has devoured the contents, with silk; divides it into two apartments, into one of which it pushes the excrement it had voided, and in the other assumes the pupa[547].

These, and the other larvæ mentioned above, commonly[Pg 233] form their cocoons of the substances I have indicated; but when by any cause they are prevented from access to them, they often substitute such other materials as are at hand. Reaumur fed a larva that formed its cocoon of minute fragments of paper, which with its mandibles it had cut from the piece that covered the glass vessel that contained it[548]: and the same circumstance happened to Bonnet.

Upon a former occasion I described to you the cases of various kinds formed and inhabited by the insects of the Trichoptera Order (Phryganea L.) commonly called case-worms[549]. As these serve for the pupa as well as the larva, they may be regarded as a kind of cocoon. I shall not repeat here what I then said; but having purchased from the collection of the late Mr. Francillon some that seem to belong to this or some cognate tribe, that are of a curious construction, I shall give you some account of two or three of them in this place. The first is not quite three inches long, of a sublanceolate shape, but rather widest towards one end. It consists of an internal tough and thick bag or cocoon, of a silk resembling fine wool of a dirty white colour, which is closely covered transversely by pieces of the stalk of a plant, about three-fourths of an inch in length, and crossing each other at an obtuse angle. The next is thicker and shorter: the internal bag is just covered with small fragments of wood like sawdust; over these are fastened irregularly, short stout pieces of a pithy stick or stalk, and the whole is clothed with a very close-woven ash-coloured web. It seems difficult to conceive how the inclosed animal could contrive to cover her habitation with[Pg 234] this web without going wholly out of it. The third is the most curious and remarkable of all. It is nearly six inches long, and about four-fifths of an inch in diameter. It consists of a bag of thick cinereous silk web, to which are fastened, in a sextuple series, pieces of stick about an inch long, the end of one mostly resting upon the base of another: between each series a space of about three-tenths of an inch intervenes, but at the apex they all converge. This probably imitates the branch or stem of some tree or plant, in which the leaves are linear, and diverge but little from the stem. A label upon it states its country to be New Holland. I suspect the inhabitants of the two last cocoons to be terrestrial animals: the first is probably a true aquatic case-worm.

The same purpose for which the cocoons above described serve, is answered in the case of numerous Dipterous insects, by a humble and less artificial contrivance—the skin, namely, of the larva; which, as was before observed[550], is never cast, but, when the insect is about to enter into the pupa state, assumes a different form and colour; becomes of a thicker and more rigid texture; and defends the included pupa, which is separate from it, till its exclusion. In this case the mouth of the larva is constantly different from that of the perfect insect, or at least has not with it those relations as to number and kind of organs, which have been observed in the mouth of other larvæ compared with the insects that they produce. The animal, immediately after it is clothed with this skin, if it is opened, exhibits only a soft gelatinous[Pg 235] pulp, in the surface of which the exterior organs of the adult insect cannot yet be detected. Nature requires more time for their elaboration, or at least for the appearance of their outline, and to consolidate them. This pulp first takes an oblong form (Boule allongée Reaum.), and afterwards that of the insect it is destined to give birth to[551]. The skin of the larva also serves for a cocoon to the pupæ of male Cocci[552]. The grub of the genus Anthrenus, so destructive to our cabinets of natural objects[553], when it assumes the pupa does not quit its skin, but only splits it open longitudinally on the back, and when it becomes an imago makes its exit through the orifice[554]. Some Lepidopterous larvæ even (Alucita pentadactyla, Callimorpha rosea, &c.) assume the pupa state within their last skin[555].

When a larva has finished its cocoon,—which with[Pg 236] some species, that proceed so earnestly as though they had not a moment to lose, is the work of a few hours, of others about two or three days,—after a certain interval it casts its last skin, which is usually suffered to remain in the cocoon (but which one moth, Geometra lacertinaria, ejects through an opening purposely left in its bottom), and the pupa makes its appearance[556]. This interval is exceedingly various. Most larvæ assume the pupa state within a few days after they have formed their cocoons; but some not for several weeks, or even months. The caterpillar of Bombyx cæruleocephala, according to Rösel, lies three weeks in the cocoon before this change is effected; those of many Pupivora and Diplolepariæ Latr., according to Reaumur, six months[557]; that of Phalæna urticata nine months[558]; and that of Cimbex lutea, according to De Geer, sometimes eighteen months[559]. Brahm observes, that such larvæ of the double-brooded moth, Hepialus Testudo, as form their cocoons in autumn, do not become pupæ until the following spring; while those which form them in summer undergo this change in a few days[560]. From this fact it might be conjectured, that the degree of heat prevailing at the time the insect incloses itself determines the period of the pupa's appearance; but this supposition seems contradicted by what Reaumur observed of a brood of the larvæ of Phalæna urticata, just mentioned, which, though they formed themselves cocoons in September, did not become pupæ till the June following[561]. I am unable, therefore, to assign any plausible cause for these extraordinary variations.[Pg 237] The difficulty of comprehending how animals before so voracious can live so long without food may be partly surmounted, by adverting to the circumstance of its having attained its full growth, and laid up a store of nutriment for the development of the perfect insect. It is consequently no more wonderful that it should not have need of any further supply without casting off its upper integument, than that it should not eat after having done so and become a pupa.

[Pg 238]

LETTER XXXI.

STATES OF INSECTS.

PUPA STATE.

We have now traced our little animals through their egg and larva states, and have arrived at the third stage of their existence, the Pupa State. This, to include all, can only be defined,—that state intervening between the larva and imago, in which the parts and organs of the perfect insect, particularly those of sex, though in few cases fully developed, are prepared and fitted for their final and complete development in the last-mentioned state; and in which the majority of these animals are incapable of locomotion, or of taking food.

Pupæ, like larvæ, may be separated into two great divisions:—

I. Those which, in general form, more or less resemble the larvæ from which they have proceeded.

II. Those which are wholly unlike the larvæ from which they have proceeded.

I. To the first division belong, with some exceptions[562],[Pg 239] the Dermaptera, Orthoptera, Hemiptera, and most Aptera, with the neuropterous tribes of Libellulina, Ephemerina, and the genus Termes, in the class Insecta; and the majority of the Arachnida. This, like the first division of larvæ, may be subdivided into two corresponding smaller sections; the first including those pupæ which resemble the larvæ, except in the relative proportion and number of some of their parts; and the second those that resemble them, except in having the rudiments of wings, or of wings and elytra.

i. The first subdivision will include the pupæ, if they may be so called[563], of insects of the Aptera order, and of the class Arachnida: as, lice, Poduræ, Lepismidæ, centipedes, millipedes, mites, harvest-men, spiders, scorpions, &c. These mostly differ from their larvæ only in that the relative length or number of their legs, the number of the segments of the body in some, or the development of their palpi, more nearly approach the characters of the perfect insect; and in that while in their larva state they have two or more skins to cast, previously to their assumption of the imago, in their pupa state they have but one. In fact, this last circumstance is the only one which, strictly speaking, characterizes the pupæ of this subdivision; as the changes which take place in the number and proportion of the organs are partly produced with each change of the larva's skin. And hence, as it is not easy to ascertain what number of skins a spider, for example, has yet to cast, and as both the larva and pupa differ so little from the perfect insect, it is very difficult to determine in what state insects of this division are. From[Pg 240] this difficulty has probably arisen the too great multiplication of species in some of these tribes, particularly the Arachnida, the larva and pupa having been mistaken for perfect insects. The pupæ of this subdivision were named by Linné complete, from the near resemblance which they bear to the imago.

ii. The second subdivision will include the pupæ of the Dermaptera, Orthoptera and Hemiptera orders, with few exceptions; as likewise the Libellulina, Ephemerina, and Termitina? amongst the Neuroptera: including the well-known tribes of earwigs, cockroaches, crickets, grasshoppers, locusts, lanthorn-flies, froghoppers (Cicada L.), bugs, plant-lice, dragon-flies, day-flies, white ants, &c. Of these, as in the former subdivision, the pupæ are equally capable of eating and moving with the larvæ, which they resemble, except in having the rudiments of wings, or of wings and elytra. The pupæ of the three orders first enumerated differ from those of the Neuroptera in resembling the perfect insect in most instances, both as to shape and the organs for taking their food; and in all other respects, except in not having their wings and elytra fully developed[564]. The resemblance of the pupæ of the Libellulina and Ephemerina to the perfect insects is more distant, and the above organs in the two states are very dissimilar; for the pupæ of the former are furnished with a prehensory mask similar to that of the larvæ before described[565], which the perfect insect has[Pg 241] not; and those of the latter with the usual oral organs of masticating insects, of which the imago has scarcely the rudiments.

I have applied the term rudiments to the wings and elytra in this state, not in a strict sense, but merely to denote their appearance; for in fact the wings, &c. are complete, but only folded up longitudinally and transversely, and inclosed in membranous cases, which when the last change takes place remain attached to the puparium or pupa-case. The tegmina or hemelytra in this state usually cover the wings, and the upper wings the under; but in the Libellulina both are usually visible. Though commonly very small compared with the instruments of flight in the perfect insect, some of these rudiments, contrasted with the majority, are of considerable magnitude. This is the case with those of some species of Chermes, as we learn from De Geer[566].

II. The second grand division comprises by far the largest number of pupæ: those of all coleopterous, strepsipterous, lepidopterous, hymenopterous, dipterous, and aphanipterous, and by far the majority of neuropterous insects, as well as the hemipterous genus Aleyrodes, and one sex of Coccus of the same order. These pupæ, however, though agreeing in the circumstance of being unlike the larvæ from which they proceed, differ from each other in several respects, and require to be divided into three great sections, as under:—

i. Those pupæ in which the parts of the future insect, being folded up under a membranous skin closely applying to each, are distinctly visible. To this head belong[Pg 242] generally, the pupæ of coleopterous[567] and hymenopterous insects; those of the neuropterous genera Myrmeleon and Hemerobius, &c.; the Trichoptera; amongst the Diptera, Culex, Tipula L., Tabanus, Bombylius, &c.; and that of the flea (Pulex). These were the incomplete pupæ of Linné.

ii. Those pupæ in which the parts of the future insect, being folded up under a harder skin, are less distinctly discoverable. To this subdivision belong the pupæ of all Lepidoptera, and of them alone. These are what Linné termed obtected pupæ.

iii. Those pupæ which are inclosed in the thick and opaque skin of the larva, through which no trace of the perfect insect can be discovered. These, which Linné termed coarctate pupæ, include a large proportion of the dipterous genera; as Œstrus L., Musca L., Empis L., Conops L., &c. &c.[568]

[Pg 243]

I shall next advert, chiefly to the pupæ of the grand division last described, under the distinct heads of substance, figure, and parts; colour, age, sex, motions, and extrication of the perfect insect.

i. As to their substance—at first interiorly all pupæ consist of a milky fluid, in which the unformed members of the future perfect insect may be said to float, and in[Pg 244] which they may be discerned, and separated with the point of a pin[569]. In proportion as these acquire consistency, and are more and more developed by the absorption of the surrounding fluid, they occupy its place, and fill up the cavity of the puparium. The rest of this fluid passes off by transpiration[570]. Reaumur is of opinion that it is from the epiploon, or corps graisseux, that this matter is prepared, which he regards as analogous to the white of an egg[571]. In coarctate pupæ the included animal, or the pulp that contains its germes (in which the limbs and body at first are not discernible), fills at this period the whole skin-cocoon; but in proportion as the above evaporation takes place, and the consolidation of the body and parts proceeds, it shrinks at each end, so that when near assuming the imago, a considerable cavity appears both at the head and tail of the cocoon[572]. At this period of its existence, from the quantity of fluid included in the puparium, the animal weighs usually considerably more than it does when become a perfect insect[573].

The exterior integument or skin of pupæ, which is usually lined with a very thin white pellicle, is of different consistence in different orders. In the Coleoptera and Hymenoptera it is, with a few exceptions, of a soft and membranous texture; in the Lepidoptera (especially those that are not defended by cocoons), and Diptera, it is more rigid and harder, being either coriaceous or corneous. Lepidopterous pupæ, however, are not excluded from[Pg 245] the last skin of the larvæ with this hard covering. At the moment of this change the envelope is nearly as soft and membranous as in the order first mentioned. But they are besides covered with a viscous fluid, which appears to ooze out, chiefly from under the wings, and which very soon drying, forms the exterior hard shell[574]. At first the antennæ, wings, and legs, like those of Coleoptera and Hymenoptera, can be each separated from the body; and it is only after these parts have been glued together by the fluid just mentioned, which takes place in less than twenty-four hours[575], that they are immoveably attached to the body of the pupa, as we usually see them. In fact, the essential difference between incomplete and obtected pupæ seems to be, that in the former the limbs and body are only covered each with a single membranous integument, whereas in the latter they are besides glued together by a substance which forms an additional and harder envelope. It is not easy to explain the alteration that takes place in the texture of the skin of such dipterous pupæ as retain the skin of the larva. In the latter this is generally a transparent and very fine membrane: yet the very same integument becomes to the pupa an opaque and rigid case.

The surface of the skin of the greater number of pupæ is smooth, but in those of many Papilionidæ it is rugose and warty: this you may see, particularly in that of Papilio Machaon. In many of the hawkmoths (Sphinx L.) it is covered with impressed puncta. In Attacus Io the upper side of the channels that separate the intermediate segments of the abdomen are curiously striated with transverse[Pg 246] striæ, formed of very minute granula, the lower side being transversely sulcated. In some few instances, as in Arctia Salicis, Laria pudibunda and fascelina, the skin of the pupa is clothed with hair[576]: as is also that of Hesperia Bixæ, according to Madame Merian[577]. De Geer has described a little beetle under the name of Tenebrio lardarius (Latridius Latr., Corticaria Marsh.), the pupa of which is beset with very fine hairs, terminating in a spherical or oval button[578].

ii. I shall include under the same head both the figure or shape, and parts of pupæ, as the latter in most kinds are either the same or nearly the same as those of the larva, or merely incasing those of the imago, so as not to require that detailed notice that I judged necessary when treating of the parts of larvæ.

With regard to incomplete pupæ, nothing further can be said of their extremely various figure, than that it has a general resemblance to that of the perfect insect. The head, trunk, abdomen, and their respective external organs, are alike visible in both; but in the pupæ, the latter, instead of occupying their natural situation, are all closely folded under the breast and abdomen: or, as in the case of the long ovipositors of some Ichneumons, laid along the back. In a specimen of some coleopterous insect now before me, the following is the order of the arrangement of the parts:—The head is inflexed; the mandibulæ are open; between them are seen the labium and labial palpi; these appear to cover and conceal the maxillæ, and the maxillary palpi extend on each side beyond them; the[Pg 247] antennæ pass above the thighs of the two anterior pair of legs, and then turning down over the breast between them and the posterior legs, repose upon the base of the wings; which also are turned down between the intermediate and posterior pair of legs, and rest upon the latter; the tibiæ are bent in and folded upon the thigh, and the tarsi turn outwards[579]. In another coleopterous species, the wings and elytra are placed under the hind-legs. In Hymenopterous pupæ the antennæ appear usually to lie between the legs[580]. In many Tipulæ the long legs are bent into three folds in the pupæ; but the tarsi are extended, and lie close to each other, the anterior pair being the shortest[581]. In a specimen belonging to this tribe in my cabinet, which I think contained Ctenocera pectinicornis, the six leg-cases are of the same length, exactly parallel and adjacent, and being annulated wear the appearance of tracheæ[582]. These parts have each their separate case, so that a pin may be introduced between them and the body: which cases, as well as the general envelope, are usually formed of a fine soft transparent membrane; but sometimes, as in the lady-bird (Coccinella), the tortoise-beetle (Cassida), the crane-fly (Tipula), &c. it is harder and more opaque, so that though it is usually easy for a practised Entomologist from an examination of the pupa, particularly in the Hymenoptera, to predict to what genus the insect to be disclosed[Pg 248] from them will belong, yet in these cases the organs being not so conspicuous, a less experienced examiner might be perplexed, and unable to come to a conclusion.

Although hymenopterous pupæ have usually no parts but what are afterwards seen in the perfect insect, this is not the case with several coleopterous and dipterous ones, which are furnished with various temporary appendages, indispensable to them to bring about their final change, or for other purposes. Thus, the pupa of the male of Lucanus Cervus has two short, jointed anal processes[583]. That of Hydrophilus caraboides has a pedunculated lunulate one; and moreover, the sides of the abdominal segments, and the top of the thorax, are beset with hairs, which are not seen in the perfect insect[584]. The abdomen of many, also, is armed with spines. That, the arrangement of whose organs I lately described, has a quadruple series in the back of this part; viz. on each of the first five segments, 3, 2, 2, 3. The five first ventral segments also have on each side three spines; the inner are incurved, the intermediate nearly upright, and the outer one recurved. These spines, except those of the innermost ventral series, terminate in a bristle. In another coleopterous species the back part of the head is armed with a pair of lateral spines, and that of the thorax with three processes, the external ones armed with a single spine, and the intermediate one with a pair. De Geer has figured the pupa of an Asilus, the head of which is armed with eight spines—two robust ones in front, and three smaller ones, connected at the base on each side. The abdominal segments, also, are fringed with spines[585]. The abdomen of the pupa of[Pg 249] Ctenocera pectinicornis is armed with several strong conical spines, pointing mostly towards the tail, which is likewise the case with that of Tipula lunata[586]. As the above pupæ are usually subterranean or subcortical, the spines assist in pushing them out of the ground, &c. The respiratory horns that proceed from the thorax of the pupæ of many of the aquatic gnats will be noticed in another place. Those of Corethra culiciformis and of some other aquatic gnat-like Diptera, have their anus furnished with a pair of oars, or natatory laminæ, by which they rise to the surface[587].

The figure of obtected pupæ, or chrysalises, is more uniform. They are commonly obtuse at the anterior extremity, and gradually contracted to a point at the posterior, or tail. The outline usually inclines to a long oval or an ellipse; but in some, as Attacus Io and Luna, the pupa is shorter and more spherical. In Geometra sambucaria it represents an elongated cone, and in Hepialus it is nearly cylindrical. In the butterfly tribe (Papilio L.) the outline is frequently rendered angular by various protuberances.

In all these pupæ may be distinguished the following parts:—first, the Head-case (Cephalo-theca), or anterior extremity; secondly, the Trunk-case (Cyto-theca), or intermediate part; and thirdly, the Abdomen-case (Gastro-theca).

1. The Head-case covers and protects the head of the inclosed imago. From its sides behind proceed the[Pg 250] antennæ-cases (Cera-theca); and before from the middle, the tongue-case (Glosso-theca). Just below the base of the antennæ-case you may discern the eye-cases (Ophthalmo-theca), surrounded on their inner side by a crescent-shaped lævigated piece, which may perhaps transmit some light to the inclosed prisoner.

2. The Trunk-case, divided into the thorax, or upper surface, extending from the head to the dorsal segments of the abdomen, and consisting of three pieces, answering to the prothorax, mesothorax, and metathorax of the perfect insect: the first answering to the prothorax small, the second covering the mesothorax very large, and the two next representing the metathorax, at first appearing to belong to the abdomen, but having no spiracle; and the breast (pectus) or under-surface reaching from the head to the ventral abdominal segments, from which proceed the wing-cases (Ptero-theca) and leg-cases (Podo-theca), which organs, with the antenna-cases and tongue-case, entirely cover, or rather form, the breast. The arrangement of the whole is as follows:—The wing-cases, which are more or less triangular, and exhibit the larger nervures of the wings, are a lateral continuation of the mesothorax, which turn downwards from the sides of the breast, and cover, or replace, the three first ventral segments of the abdomen. The antenna-cases, united to the anterior portion of the head just behind the eye-cases, repose immediately next to those of the wings running parallel with their inner margin. Then follow the legs, the tibiæ forming an angle with the thigh, and the case of the anterior pair being innermost, and representing the breast-bone in the pupa. The tongue lies over the forelegs,[Pg 251] except in the case of some sphinxes, which I shall notice afterwards: so that the glosso-theca covers both them and it.

3. The abdomen-case consists of nine segments when viewed on the back, and of only six when viewed below; so that it might be said to have ten dorsal and six ventral segments: but the fact is, that the place of the three anterior ventral segments, or rather ventral portions of the segments, (for they form complete rings without any lateral suture,) are replaced by the wings and other organs: in consequence of this, the fourth segment, which is less covered than the three first, at its posterior margin forms an annulus or ring. In counting the abdominal segments of a pupa, you must be careful not to include the piece that represents the metathorax, which looks as if it belonged to the abdomen[588]. In the pupæ of butterflies you will discover evident traces of ten dorsal segments; but in many moths, and some hawk-moths, you will perceive at first only eight, or even seven, but a closer examination will enable you to discover the line that marks out the others; and if you divide the puparium longitudinally, and inspect its internal surface, you will see very visible sutures between them. The intermediate segments are sometimes separated from each other and the preceding and subsequent ones by deep channels. In the pupa of Papilio Machaon there is one such channel between the third and fourth segments. In Bombyx[Pg 252] regalis the channel is between the sixth and seventh, and in B. imperatoria there are three, namely, a channel between the third and fourth, and fourth and fifth, and fifth and sixth segments. The way in which insects with an exserted sting fold it in the pupa seems not to have been noticed; but from an observation of De Geer upon one species of Ichneumon, it appears to be turned up over the back of the abdomen[589].

These little animals, thus swathed and banded, exhibit no unapt representation of an Egyptian mummy; though Lamarck applies the term Mumia to incomplete pupæ[590], to which it seems less happily applicable.

Chrysalises, as to the modifications of their general figure, may be conveniently divided into two great classes: first, those that have no angular projections, the anal mucro of some excepted, on different parts of their body; and secondly, those which have such projections. Each of these classes affords variations in its peculiar characters which require to be noticed.

1. The first of these are called angular pupæ[591], and are confined to the Butterfly or diurnal tribes. In some the head projects into one short conical protuberance: this you may see in the chrysalis of the common cabbage butterfly (Pieris Brassicæ), and others of the same genus[592]; in the brimstone-butterfly (Colias Rhamni[593]), and in the beautiful purple emperor or high-flier (Apatura Iris F.[594]): though in this last it is not conspicuous. But[Pg 253] the most remarkable instance of a single eminence from the head is exhibited by the pupa of a tropical butterfly (Morpho Idomeneus Latr.), figured by Madame Merian. In this the head projects into a long incurved obtuse horn[595]. In others the head is armed with two mucros, or conical eminences. This is the case with the common butterfly of the nettle (Vanessa Urticæ F.[596]), and with that of the beautiful Papilio Machaon[597]. In these the prominences are trigonal. These processes, which in some, as in the peacock-butterfly (Vanessa Io), stand upright[598], and in others diverge (Papilio Machaon), form the eye-cases of the included imago; and in their outer base is planted the crescent-shaped piece I lately mentioned, which seems intended to convey light into it. In many the prothorax, besides a lateral angular projection, has in the middle another triangular or trigonal one, somewhat resembling a Roman nose; on each side of which is a smaller elevated black point: so that it requires no great stretch of imagination to find out in it a sort of resemblance to the human face, which, though not quite so striking as honest Goedart figures it[599], is however very considerable. In the pupa of Morpho Menelaus, figured by Madame Merian[600], this nasiform prominence of the prothorax is extended into a long arched horn, reaching to the middle of the abdomen. The pupa of the silver-washed fritillary (Argynnis Paphia F.), and others of the same genus, exhibit beneath this nasiform prominence[Pg 254] a very deep depression, itself beset with one or more series of smaller angular elevations. The back of the abdomen is often furnished with two rows of protuberances, in some species larger, in others smaller[601]; sometimes sharp and conical, and sometimes flat, and in some instances resembling the fins of fishes[602]. These bosses usually decrease in size towards the tail.

2. The second kind of chrysalises are denominated conical[603]. These, which include the crepuscular and nocturnal Lepidoptera, and the butterflies with onisciform larvæ, have no protuberances, and are less variable in their form—their anterior extremity being almost constantly oval and rounded, and their posterior conical and acute. An exception to this form is met with in the pupa of a moth long celebrated (Lasiocampa Pithyocampa)[604], which has the head acute and the tail obtuse, and armed with two points[605]. Another occurs in that of the Cossus, which has two points on the head, by which it makes an opening in its cocoon: when it assumes the imago, one of these is placed below the other[606]. And some few have the anterior end nearly flat instead of rounded. The pupa of the orange-tip butterfly (Pieris Cardamines) seems intermediate between the angular and conical kinds: it is somewhat boat-shaped, and distinguished by a fusiform process from the head and tail[607]. Other modifications of the usual figure are met with, but are for the most part so slight as not to require notice. One[Pg 255] or two, however, should not be passed over. The pupæ of many hawk-moths (Sphinx L.) have the anterior piece of the head-case elongated into a sort of cylindrical proboscis, which is incurved beneath the breast: you will find this formation in S. Convolvuli and Ligustri[608]. In some, as in a species figured by Madame Merian, that feeds upon the Annona squamosa, it is rolled up like a serpent in many folds[609]. In Noctua Linariæ the tongue-case turns upwards, and is prominent laterally beyond the body[610]. This singular appendage is one of those beautiful instances of compensating contrivances, as Dr. Paley calls them, which perpetually occur in the insect tribes. The tongue of these hawk-moths is of very great length, often three inches, while the pupa itself is scarcely two; it could not possibly, therefore, have been extended at length, as it is in common cases, but is coiled up within the above protuberance. When the tongue is but a little longer than the breast, the ordinary plan is adhered to, but the apex of the breast projects a little over the abdomen into a sort of nose, in which the end of the tongue is contained. This conformation may be seen in the pupa of Noctua Gamma, Verbasci, and many other species. Sometimes, as in N. Linariæ F., this projection is recurved into a short horn.

I have before adverted to the adminicula or short spines looking towards the anus, with which the dorsal segments of the abdomen of some pupæ are armed; and by which, when the time for their exclusion is arrived, they are enabled to push themselves upwards or outwards from[Pg 256] their several places of confinement[611]: you will find these in the pupa of the great goat-moth (Cossus ligniperda); and in the cylindrical pupa of the moth called the ghost (Hepialus Humuli F.) there are two rows of sharp triangular spines on the back of each segment. These are not laid flat, but, as they do also in the Cossus, form an acute angle with the body; which gives them greater power of resistance. Those that constitute the row nearest the base of the segment are longer than the anterior row, the middle spines than the lateral ones. The first and last segment are without them, and the last segment but one has a sharp ventral transverse ridge, armed with many sharp teeth[612]. The abdominal spines lately mentioned, of semicomplete pupæ, are also adminicula.

The tail of this description of pupæ is in many instances armed with a mucro, or sharp point, emerging from its upper side. You will see this in most hawk-moths. In the pupa of Hesperia Proteus the mucro is truncate at the apex; in that of Bombyx imperatoria it is long, and terminates in two diverging points. In the majority of chrysalises of both descriptions the tail is acute, and usually furnished with hooks of different kinds. These are so various in shape and number, &c. that they would probably afford good characters for discriminating many allied species. In some there are but two or three, in others five or six, in others they are more numerous[613]. Sometimes they are quite straight[614], but most commonly recurved, so as to form a hook. The hawk-moths, and a[Pg 257] few others, as Bombyx Pini, Cerura Vinula, &c., have no anal hooks whatever. Under this head I shall observe, that in many conical pupæ below the anal angle or mucro, is the appearance of a vertical foramen or passage: this is particularly conspicuous in Hepialus, in which it is surmounted by a bifid ridge, and has under it a pair of minute black tubercles.

A pretty accurate judgement of the division to which the perfect insect when disclosed will belong, may usually be formed from the figure of its chrysalis. All the angular ones, with scarcely any exception, inclose butterflies. The converse, however, does not hold; for some that are not angular, as those of Parnassius Apollo and Mnemosyne, and most of the Linnean Plebeii urbicolæ, also inclose flies of that description. With these exceptions, all conical chrysalises give birth to moths or hawkmoths. An idea even of the family or genus under which the perfect insect will arrange, may be generally formed from the figure of the chrysalis; less distinctly, however, in the conical or rounded, than in the angular kinds, in which the prominences of the head and trunk, as before explained, usually vary in different families. Even the sex of some moths may be judged from the pupæ: those of females being thicker; and those also of the females that have no wings, or only the rudiments of them, will of course vary somewhat from the ordinary form: but there is a still more striking difference in that of Callimorpha? vestita F., and others of the singular tribe before noticed[615], called by the Germans Sacktrager (sack-bearers), from the sack-like cases in which the larva resides. The[Pg 258] females of these having not only no wings, but no antennæ, and legs not longer than those of the larva, their pupa more resembles that of a dipterous than of a lepidopterous insect, it being not easy to determine which is the head and which the tail[616].

In these too we can often learn from the outline of the wing-cases, whether the inhabitant of the chrysalis has these organs indented or intire. If the former, the margins of these cases are sinuate, as in that of Vanessa C. album; if the latter, they are intire, as in Pieris Brassicæ. Even in conical pupæ,—the size, the shape of the antennæ, which may be distinguished through the skin that covers them, and slight modifications of the ordinary form,—give indications of the genus of the included insect sufficiently conclusive to a practised eye.

The true figure of coarctate pupæ when they are mature, the parts of the future fly being very visible, and each being included in a separate case[617], is that of those that belong to the incomplete division; but as this is a character not cognizable without dissection, it is customary, in speaking of pupæ of this description, to refer solely to the shape of the exterior covering, which is in fact a cocoon formed of the dried skin of the larva moulded into a different form. In this sense the figure of coarctate pupæ is extremely various. The majority of them are more or less oval or elliptical, without any distinct parts, were it not that they usually retain traces of the segments which composed the larva's body[618]. Of this figure are the pupæ of the common cheese-maggot[619], and many other flies. Others[Pg 259] (Sepedon Latr.) have the pupa shaped like a boat. That of Scæva Pyrastri F. assumes the figure of a flask; or, according to Reaumur's more accurate comparison, of a tear[620]. The tail of many of these pupæ, particularly of aquatic species, is elongated into a sort of beak, either simple or forked, or is beset with spines variously arranged. The pupa of Stratyomis Chamæleon, and other allied species, differs from all the rest of this subdivision in retaining the exact form of the larva[621]; and hence constitutes an exception to the general character of our second great Division.

iii. There is much less variety in the colour of pupæ than in that of larvæ. The majority of coleopterous and hymenopterous pupæ are white, or whitish; of lepidopterous and dipterous, brown of various shades, often verging on black in the former and on red in the latter. The angular lepidopterous ones, however, are more gaily decorated. Some, Pieris Brassicæ, are of a greenish yellow, marked with spots of black; others are of a uniform green, Apatura Iris, Pieris Cardamines; others, reddish, Vanessa C. album; others again red with black spots, Urania Leilus[622]. A still greater number shine as though gilded with burnished gold—either applied in partial streaks, Vanessa Cardui; or covering the entire surface, Vanessa Urticæ. It was from this gilded appearance in some obtected pupæ that the terms Chrysalis and[Pg 260] Aurelia were applied to the whole. The alchemists mistook this for real gold; and referred to the case as an argument in favour of the transmutation of metals. But Reaumur has satisfactorily shown, that in this instance the old proverb is strictly applicable—"All is not gold that glitters." He found that this appearance is owing to the shining white membrane immediately below the outer skin, which being of a transparent yellow gives a golden tinge to the former; in the same way that tinfoil, when covered with a yellow varnish, assumes the metallic appearance which we see in gilt leather. He mentions, too, that for the production of this effect—it is essential that the inner membrane be moist: whence may be explained the disappearance of the gilding as soon as the butterfly is ready to escape from the pupa. The shade of colour in these gilded chrysalises is various: some are of a rich yellow, like pure gold; others much paler; and some nearly as white as silver. That of Hipparchia Cassiæ F. is red with silver spots[623].

Though by far the greater number of the chrysalises of moths are of an uniform chestnut, brown, or black,—a few are of other colours; as that of Geometra alniaria, which is of a glaucous blue; of Noctua sponsa, lilac; and of Noctua pacta, of a lovely blue, caused by a kind of bloom, like that of a plum, spread upon a brown ground. A similar bloom is found on that of Parnassius Apollo, and on the anterior part of that of Platypterix cultaria and sicula; in which last, Kliemann observed it to the[Pg 261] be renewed when rubbed off[624] Many pupæ have the sheaths of the wings of a different colour from that of the rest of the body; a few are variegated with paler streaks or bands, as Clostera Anastomosis, which has two red longitudinal stripes down its dark-brown back; and that of the common gooseberry and currant moth, which may be found in every garden, has alternate rings of black and yellow[625].

A few pupæ vary in their colour, as the painted lady-butterfly (Vanessa Cardui), some of which are light-brown with gray streaks and golden dots, others wholly of a golden yellow or brown, others of a light green[626].

Almost all at their first assumption of the pupa state have a different colour from that which they take a few days afterwards. This last they retain until the disclosure of the perfect insect; except some that have transparent skins, which a few days previously to this period exhibit the colours of the included animal.

iv. There is as great variety in the length of the age of Insects in their pupa as in their larva state. Some species continue in it only two or three days (Aleyrodes Chelidonii Latr., Tinea proletella L.); others, as many weeks, or months, or even years. Each, however, has in general a stated period, which in ordinary circumstances it neither much exceeds nor falls short of. The only general rule that can be laid down is—that small pupæ continue in that state a shorter time than those of larger bulk. Thus, amongst coleopterous genera, the more minute species of Curculio L.; amongst the Hymenoptera,[Pg 262] the Ichneumones minuti L.; amongst the Lepidoptera, the subcutaneous tribes; and the majority of the Diptera,—remain as pupæ only a few days or weeks: while the larger species in all these orders commonly exist in the same state several months—many even upwards of two years. There are, however, numerous exceptions to this rule; for some large pupæ are disclosed in a much shorter time than some others not a twentieth part of their bulk.

The reasons both of the rule and of the exceptions to it are sufficiently obvious. And first, as to the rule:—If you open a pupa soon after its assumption of that state, you will find its interior filled with a milky fluid, in the midst of which the rudiments of its future limbs and organs, themselves almost as fluid, swim. Now the end to be accomplished during the pupa's existence is, the gradual evaporation of the watery parts of this fluid, and the development of the organs of the inclosed animal by the absorption and assimilation of the residuum. Reaumur, by inclosing a pupa in a stopped glass tube, collected a quantity of clear and apparently of pure water, equal to eight or ten large drops, which had evaporated from it, and was condensed against the sides of the tube, and it was found to have lost an eighteenth part of its weight[627]. It is plain, therefore, that this necessary transpiration, other circumstances being alike, must take place sooner in a small than in a large pupa. Next, as to the exceptions:—Since the more speedy or more tardy evaporation of fluids depends upon their exposure to a greater or less degree of heat, we might à priori conclude, that pupæ[Pg 263] exposed to a high temperature would sooner attain maturity, even though larger in bulk, than others exposed to a low one:—and this is the fact. The pupa of a large moth, which has assumed that state in the early part of summer, will often disclose the perfect insect in twelve or fourteen days; while that of an Ichneumon, not one hundredth part of its size, that did not enter this state till late in autumn, will not appear as a fly for seven or eight months. But this is not the whole. The very same insect, according as it has become a pupa at an earlier or later period of the year, will at one time live but a few weeks, at another several months, in that state. Thus, if the caterpillar of Papilio Machaon, one of those which has annually a double brood, becomes a pupa in July, the butterfly will appear in thirteen days: if not until September, it will not make its appearance until the June following; that is, not in less than nine or ten months: and the case is the same with the pupæ of Noctua Psi, and of a vast number of other insects. To put beyond all doubt the dependence of these remarkable variations on temperature merely, it was only necessary that they should be effected, as Lister long ago advised[628], by artificial means. This Reaumur accomplished. In the month of January he placed the chrysalises of several moths and butterflies, which would not naturally have been disclosed until the following May, in a hothouse: the result was, that the perfect insects made their appearance in less than a fortnight, in the very depth of winter; and by other numerous and varied experiments he ascertained, that in this heated atmosphere five or six days[Pg 264] hastened their maturity more than as many weeks would have done in the open air. The disclosed insects were in every respect perfect, and the females, after pairing, laid their eggs, and then died, just as if they had not been thus prematurely forced into existence. The converse of this experiment equally succeeded:—by keeping pupæ the whole summer in an icehouse, Reaumur caused them to produce the fly one full year later than their ordinary period[629].

This extraordinary fact leads us to a very singular and unexpected conclusion—that we have the power of lengthening or shortening the life of many insects at pleasure; that we can cause one individual to live more than twice as long as another of the same species, and vice versâ. Had Paracelsus made this discovery, it would have led him to pursue his researches after the elixir of immortality with redoubled confidence, and would have supplied him with an argument for the possibility of prolonging the life of man beyond its usual term, which his sceptical opponents would have found some difficulty in rebutting. Even the logical Reaumur seems inclined to infer from it, that this object of the alchemists was not so chimerical as we are wont to conclude[630]. He confesses, however, if it were to be attained only by the same process as effects the extension of an insect's life—by prolonging its state of torpor and insensibility,—that few would choose to enjoy it on such conditions. The man of pleasure, blunted by excess of use to all modern stimuli, might perhaps not object to a sleep of a hundred years, in the hope of finding something new under the[Pg 265] sun when he waked; and an ardent astronomer would probably commit himself with scientific joy to a repose as long and as sound as that of the seven sleepers, for the chance of viewing his predicted return of a comet, on stepping out of his cave: but ordinary mortals would consign themselves to the perils of so long a night with reluctance, apprehending a fate no better than what befel the magician, who ordered himself to be cut in small pieces and put in pickle, with the expectation of becoming young again[631].

The duration, then, of an insect's existence in the pupa state, depends upon its bulk, upon the temperature to which it is exposed, and upon a combination of these two circumstances. This experiment appears very simple. We seem to ourselves to have accomplished what is so often undertaken in vain—to have found an entrance into the cabinet of Nature, and to have made ourselves masters of the contents of one of the pages of her sealed and secret book. We deceive, ourselves, however: this book, when it seems most legible, is often interlined with sympathetic inks, if I may so speak, which require tests unknown to us for their detection. If you lay up a considerable number of the pupæ of a moth now called Eriogaster lanestris, the larva of which is not uncommon in June on the black-thorn, selected precisely of the same size, and exposed to exactly the same temperature, the greater number of them will disclose the perfect insect in the February following; some not till the February of the year ensuing, and the remainder not before the same[Pg 266] month in the third year[632]. Mr. Jones of Chelsea, a most acute lepidopterist, in one of his excursions captured a female of Arctia mendica, another moth, which laid a number of eggs, thirty-six of which produced caterpillars: all these fed, spun their cocoons, and went into the pupa state in the usual manner, but at the proper season only twelve produced the fly. As this was no uncommon circumstance, he concluded that the rest were dead: to his great astonishment, however, in the next season twelve more made their appearance; and the following year the remainder burst into life, equally perfect with the foregoing[633]. In this extraordinary result, which also occasionally has been observed to take place in the emperor-moth (Saturnia pavonia), the privet-hawkmoth (Sphinx Ligustri), and that of the spurge (S. Euphorbiæ)[634], and other species,—it is clear that something besides mere size and temperature is concerned: for, these circumstances being precisely alike, one pupa arrives at maturity in six months, and another of the same brood requires between two and three years. We can guess, that the end which the All-wise Creator has in view, in causing this remarkable difference, is the prevention of all possibility of the destruction of the species. Eriogaster lanestris and Arctia mendica, &c., for instance, are doomed, for some reason[Pg 267] unknown to us[635], to be disclosed from the pupa in the cold and stormy months of February and March, almost every day of which in certain years is so ungenial that few insects could then survive exposure, much less deposit their eggs and ensure the succession of a progeny. Now, were all these to make their appearance in the perfect state in the same year, it might happen that the whole race in a particular district would be destroyed. But this possibility is effectually guarded against by the beautiful provision under consideration, it being very improbable that three successive seasons should be throughout unfavourable; and without such occurrence, it is clear that some of the race of this moth will be preserved. In the case of other moths, whose pupæ though disclosed in the summer are governed by the same rule, the prevention of the extinction of the species, by any extraordinary increase in a particular year of their natural enemies, seems the object in view[636]. But though the intention be thus obvious, the means by which it is effected are impenetrably concealed. What physiologist would not be puzzled with the eggs of a bird, of which one-third should require for their hatching to be sat upon only a fortnight, another third a month, and the remainder six weeks? Yet this would be an anomaly exactly analogous to that observed by Mr. Jones with respect to the pupæ of A. mendica. Reaumur found that when the skin of pupæ was varnished, so as to prevent absorption, the appearance of[Pg 268] the fly happened nearly two months later than in ordinary circumstances. Are we to conjecture that those of the moth just mentioned, or of E. lanestris, that are latest matured, from a greater degree of viscidity in the fluid that forms them[637], have thicker and more impervious skins than those disclosed at an earlier period? Or are we to refer the difference to some unknown peculiarity of organization? On any supposition, the fact remains equally wonderful; and I know of none the illustration of which is more worthy of the patient investigation of the physiologist.

As the period of maturity of the perfect insect is thus in some cases not fixed even to years, and as in many it seems dependent upon such variable causes; nothing appears more improbable than that it should ever be so strictly determined, that even the week in which the fly will leave its pupa-case can be pretty accurately predicted. Such, however, is the fact with regard to the Ephemera so interestingly described by Reaumur, the myriads of which that issue from the banks of the Seine all appear in two or three days, somewhere between the 10th and 18th of the month of August[638] in every year; at which time the fishermen regularly expect them. A like regularity attends the appearance of those described by Swammerdam, which every year, for three days about the feast of St. John, issue in clouds from the Rhine[639]—Not only is the week fixed, but in several instances even[Pg 269] the hour. The Ephemeræ observed by Reaumur appear at no other time than between eight and ten o'clock in the evening; and so unalterably is their exclusion fixed, that neither cold nor rain can retard it. Between these hours, in the evenings on which they appear, you may see them fill the air, but an hour before or after, you will in vain look for one[640]. So also the silkworm-moth and the hawkmoth of the evening primrose (Sphinx Œnotheræ) constantly break forth from the pupa at sunrise: and the hawkmoth of the lime (Smerinthus Tiliæ) as certainly at noon[641]. Schroeter states, that of sixteen specimens of the death's-head-hawkmoth (S. Atropos) which he bred, every one was disclosed between four and seven o'clock in the afternoon[642].

Before I conclude this head, I must observe, that after a caterpillar or gnat has spun its cocoon, it sometimes remains for a considerable period before it incloses itself in the pupa-case, and casts off the form of a larva. Thus the little parasite (Ichneumon glomeratus L.) that destroys the caterpillar of the common cabbage-butterfly, remains a larva in its cocoon for many months, but it becomes a perfect insect a few days after it has put on its puparium[643]; and the caterpillars of the great goat-moth (Cossus ligniperda), if they spin their cocoon in the autumn, remain in it through the winter in the larva state; whereas, if they inclose themselves in the month of June, they assume the pupa, so as to appear as flies in three or four weeks[644]. It is not therefore easy to state precisely[Pg 270] the age of those pupæ which are produced from larvæ that spin cocoons.

v. I have not much to say with regard to the sex of pupæ. The male is probably to be distinguished from the female by being smaller; but in the first great division of pupæ, those which resemble the larvæ, and are locomotive, the female in numerous cases may be known by the Ovipositor, or instrument for depositing her eggs in their proper station: and the male also has his anal instruments. Sometimes in this state the animal is so matured, as to be capable of continuing its kind. I have found the pupæ both of a Gryllus L. and of a Cimex L. in coitu.

vi. Though the pupæ of the second great division are usually not locomotive, yet I must not omit some notice of their motions. As the legs of insects in this state are folded within a common or partial integument, of course none of the pupæ now under consideration, with the exception of those of the Trichoptera order, can walk: coarctate ones are even incapable of the slightest motion, and exhibit no symptom whatever of animation. Some of those that are termed incomplete, however, and most chrysalises, have the power of communicating to their bodies a slight movement, extending more or less in different species, which is effected by the abdominal segments solely. The latter, during the first twelve hours of being pupæ, when their skin is soft, frequently turn[Pg 271] themselves, that the side on which they lie may not be flattened; afterwards by far the majority merely wriggle or twist their abdomen when touched, or in any way incommoded or disturbed. We learn from De Geer, that the pupa of the ghost-moth (Hepialus Humuli), the cocoon of which is more than twice the length of the chrysalis, moves in it from one end to the other[645]. Bonnet observed one of a moth (perhaps Lasiocampa Quercus), which alternately fixed itself at the top and bottom of its spacious and obliquely-fixed cocoon; descending slowly, but ascending as quickly, and almost in the same manner, as a chimney-sweeper in a chimney[646]. The pupa of the weevil of the water-hemlock (Lixus paraplecticus) will move from one end of the interior of a branch to another by means of its adminicula, aided by the motion of its abdominal segments[647]. But the most locomotive of pupæ of the second division are those of gnats, and many Tipulidans, which pass this state in the water. These will move from the bottom to the surface, and back again, with great facility and velocity. I have before mentioned several other motions of pupæ[648], which I shall not repeat here, by which they extricate themselves from their several places of intermediate repose, before they leave the puparium: if the imago were to be disclosed in the interior of a tree, or in the earth, its wings would be materially injured in forcing its way out. The object of several of the above motions may be to alarm insects that might attack these defenceless beings. The twirling motion in particular, formerly noticed[649], in some species, by[Pg 272] causing a rustling against the sides of the cocoon, makes a considerable noise—so singular in that of a red underwing-moth (Noctua pacta), that Rösel tells us, (who by the by was more timid than becomes a philosopher,) that the first time he heard it, he had nearly thrown away the box that contained it, in his fright[650].

vii. We are next to consider The extrication of the perfect insect from the puparium, or pupa-case, and from the cocoon. The period when the pupa has attained maturity, and the inclosed insect is ready to burst the walls of its prison, may be often ascertained. Just at this time the colour frequently undergoes an alteration, the golden or silver tint of the gilded chrysalises vanishes; and those which are transparent, usually permit the form and colours of the insect within and the motions of their limbs to be distinctly seen through them. In the Libellulina the eyes become more brilliant[651]. The mature pupæ of the moth lately mentioned (Eriogaster lanestris) have a particular swell of the abdominal segments, not apparent in those that are to continue till another season, or longer[652]. Those of the case-worms (Trichoptera) push off the grates from the cases which they have hitherto inhabited, and swim about[653]. Other signs and motions doubtless predict the approach of this great change in other species, which have not been recorded.

The mode in which insects make their way out of the puparium differs in different orders. In obtected pupæ, the struggles of the included butterfly or moth first effect a longitudinal slit down the middle of the thorax, where[Pg 273] there is usually a suture for the purpose. The slit rapidly extends along the head, and down the parts which compose the breast, and the insect gradually withdraws itself from its case. It is not, however, from the outer skin merely that it has to disengage itself, but also from a series of inner membranous cases, which separately inclose the antennæ, proboscis, feet, &c., as a glove does the fingers; and similar cases inclose the parts of the perfect insect in pupæ of all the other orders. This is sometimes a work of difficulty, but ordinarily it is effected with ease.

Incomplete and semicomplete pupæ undergo nearly the same process, save that in them the body is not swathed up in a common case; and therefore they have only to liberate themselves from the partial cases that envelop the several parts of their body.

In coarctate pupæ, as those of Muscidæ, Syrphidæ, Œstridæ, &c., the process is different. Their outer-case is ordinarily more rigid and destitute of the sutures, which in the former tribes so easily yield to a slight effort. Yet in these, at the anterior end under which the head of the fly lies, and from which it always issues, there is commonly a sort of lid, joined by a very indistinct suture to the rest, which can be pushed off, leaving a sufficient opening for the egress of the insect. In the pupæ of many of this tribe this lid is composed of two semicircular pieces, which can be separately removed. Many species seem to be able to force off the lid of their puparium, by merely pushing against it with their heads: but the common flesh-fly and many other Muscidæ, which are perhaps too feeble to effect this, or whose puparia are stronger than ordinary, are furnished with a very remarkable[Pg 274] apparatus for this express and apparently sole purpose. They are gifted with the power of introducing air under the middle part of the head, to which the antennæ are fixed, and of inflating that part into a sort of membranous vesicle as big as the head itself; by the action of which against the end of the pupa-case, the lid is soon forced off. So powerful is this singular lever, that it is even sufficient to rupture the fibrous galls in which the pupæ of the gay-winged Tephritis Cardui[654] are inclosed. That it is designed by Creative Wisdom to answer this sole purpose seems proved, from its disappearing soon after the disclosure of the fly, whose head shortly becomes all alike hard. Reaumur suspects that it may also be intended to promote the circulation of the insect's fluids; but to me his reasons appear not conclusive[655]. In one instance a mode still more unexpected obtains. The illustrious naturalist just named found that the fly which proceeded from one of the rat-tailed grubs (Elophilus Latr.) had actually the power of completely reversing its situation in its narrow case; and that it then employed its tail in pushing off the lid, which other species remove by means of their heads[656].

The extrication of insects whose pupæ are above ground, like those of butterflies, many beetles, flies, &c., is comparatively a simple operation. But what, you will ask, becomes of those species whose pupæ are concealed deep in the earth, or in the heart of the trees on which their larvæ have fed? Of this you shall be informed.—Coleopterous insects disclosed from pupæ thus circumstanced,[Pg 275] wait until their organs have acquired strength, and their elytra are sufficiently hardened to protect their filmy wings from damage in forcing their way through the earth or wood which covers them. Thus Oryctes nasicornis, a rhinoceros beetle common on the Continent, is a full month before it reaches the surface of the earth, after quitting its puparium. But it is evident that no delay would enable lepidopterous or dipterous insects, which are without elytra, to make their way out of such situations, without irreparable injury to their delicate wings. Many of these, therefore, while still within the hard case of the pupa, have the precaution, a few days previously to their exclusion, to force themselves up to the surface of the earth, or, when they reside in the interior of trees, to the entrance of their hole. This is effected by a successive wriggling of the abdominal segments, which in several species, of the Coleoptera, Lepidoptera, and Diptera orders, for this purpose, as has been more than once observed[657], are furnished with sharp points (adminicula), admitting a progressive, but not a retrograde motion. The puparia of the great goat-moth (Cossus ligniperda) may be often seen projecting from orifices in willow-trees; and those of the common crane-fly (Tipula oleracea) from the surface of the earth, to which they have thus made their way from a depth of several inches.

In all the preceding instances the exclusion of the perfect insect is complete, as soon as it has withdrawn itself from the puparium. But to a very large number, even after this is effected, the arduous task still remains of[Pg 276] piercing the cocoons of leaves, of thick silk, of tough gum, or even of wood, in which the pupæ are incased. We can readily conceive how the strong jaws of coleopterous and hymenopterous species may be employed to release them from their confinement. But what instruments can be used for this purpose by moths in a state of great debility, whose mouth has nothing like jaws—merely a soft membranous proboscis? How shall the silkworm-moth (B. Mori) force its way through the close texture of a silken ball, through which the finger could not be easily pushed? Or the puss-moth (Cerura Vinula) pierce the walls of its house of glue and wood, which scarcely yield to the knife? You will not doubt that these difficulties have been foreseen by Infinite Wisdom, and provided against by Infinite Power. The egress of moths from their cocoons is secured in two ways;—either by some peculiarity in the first construction of the cocoon by the caterpillar, or by some process which the pupa or perfect insect is instructed to perform. As examples of each, several curious instances may be cited.

The larva of the moth which about 1760 made such havoc in the province of Angoumois in France, becomes a pupa in the interior of the grain of wheat which it has excavated; but the opening by which it first entered is not bigger than a pin's point, and is quite insufficient for the egress of the moth. How, then, is the latter to force its way through the tough skin which surrounds it? The larva, previously to assuming the pupa state, gnaws out a little circular piece at that end of the grain where the head of the future moth would lie, taking care not to detach it entirely. At this little door, which is sufficient to protect it from intruders, the moth has but to push, when it[Pg 277] falls down, and leaves a free passage for its exit. A contrivance almost similar is adopted by a caterpillar which feeds in the interior of the heads of a species of teazel (Dipsacus L.), for a minute and interesting history of which we are indebted to Bonnet. This caterpillar previously to its metamorphosis actually cuts a circular opening in the head, sufficiently large for the egress of the future moth; but to secure this sally-port during its long sleep, it artfully closes it with fibres of the teazel, closely but not strongly glued together[658]. Another small caterpillar described by the same author, resides in the leaf of an ash curiously rolled up into a cone, and then assumes the pupa, which is inclosed in a silken cocoon, ingeniously suspended by two threads like a hammock in the middle of its habitation, and of so slight a texture that it presents no obstacle to the extrication of the moth. It is the closely-joined sides of its leafy dwelling that form a barrier, which, were it not for the precaution of the larva, would be impenetrable to so small and weak an animal. The little provident creature, before its change to a pupa, gnaws in the leaf a round opening, taking care not to cut through the exterior epidermis. This door is to serve the moth for its exit, like that formed by the wheat-caterpillar. But in proportion to its bulk its verdant apartment is of considerable size. How then shall the moth know the exact place where its outlet has been traced? How, without a clue, shall it discover in its dark abode the precise circle which requires only a push to throw it down? Even this is foreseen and provided against. Out of twenty positions in which its hammock[Pg 278] might have been slung, the caterpillar has been directed so to place it, that the silken cord that suspends the head is fastened close to the side of the door which it has previously constructed; and the moth, guided by this filum ariadneum, at once makes its way out of an apartment which, but for this contrivance, might have been to it a labyrinth as inextricable as that of Minos[659].

The mode in which other caterpillars provide for their extrication, when become moths, from their silken cocoons, is not less ingenious. Those of Eriogaster lanestris (of which I have lately said so much,) and others, form oblong cocoons, which, viewed externally, you would at the first glance assert were of one solid piece: but on examining them more narrowly, you perceive one end of them to be a distinct lid, of a size large enough to permit the moth to issue out; and that it is kept in its place by a few slight threads, easily broken by pressure from within[660]. A few pages back[661] I mentioned a cocoon formed by the larva of Tortrix prasinana, of the shape of a boat reversed, composed of two inclined walls fastened together at the top and ends. In constructing this cocoon, it firmly glues to each other the top and one end, so as to form an impermeable suture; but the other end, at which the moth is to issue, though externally it seems as strong as the rest, is merely drawn close by a slender thread or two fastened on the inside, and easily broken from within. And, what is particularly singular in the construction of this ingenious habitation, the sides forming the end last mentioned, though originally requiring force to draw[Pg 279] them into their required position, become so elastic as to close again when the moth has passed between them and made her escape; the cocoon preserving its usual shape, even when deprived of its inhabitant[662]. A similar cocoon is constructed by another leaf-rolling caterpillar, that of Tortrix chlorana[663]. Many similar proofs of contrivance in the construction of silken cocoons might be adduced, but I shall confine myself to one more only—I mean that furnished by the flask-shaped brown one of Saturnia Pavonia, and some other moths. If you examine one of these cocoons, which are common enough in some places on the pear-tree or the willow, you will perceive that it is generally of a solid tissue of layers of silk almost of the texture of parchment; but at the narrow end, or that which may be compared to the neck of the flask, that it is composed of a series of loosely-attached longitudinal threads, converging, like so many bristles, to a blunt point, in the middle of which is a circular opening[664]. It is through this opening that the moth escapes. The silk of its cocoon is of so strong a texture and so closely gummed, that had both ends been similarly closed, its egress would have been impracticable; it finds, however, no difficulty in forcing its way through the aperture of a sort of reversed funnel, formed of converging threads that readily yield to pressure from within. But an objection will here probably strike you. You will ask, Is not this facility of egress purchased at too dear a rate? Must not a chrysalis in an open cocoon be exposed to the attacks of those ichneumons of which you have said so much, and of numerous other enemies, which will find[Pg 280] admittance through this vaunted door? Our caterpillar would seem to have foreseen your dilemma; at least, under heavenly guidance, she has guarded against the danger as effectually as if she had. If you cut open the cocoon longitudinally, you will see that within the exterior funnel-shaped end, at some distance she has framed a second funnel, composed of a similar circular series of stiff threads, which, proceeding from the sides of the cocoon, converge also to a point, and form a sort of cone exactly like the closed peristome of a moss; or, to use a more humble though not less apt illustration, like the wires of certain mousetraps[665]. In this dome not the slightest opening is left, and from its arched structure it is impenetrable to the most violent efforts of any marauders from without; whilst it yields to the slightest pressure from within, and allows the egress of the moth with the utmost facility. When she has passed through it, the elastic threads resume their former position, and the empty cocoon presents just the same appearance as one still inhabited. Rösel relates with amusing naïvété how this circumstance puzzled him the first time he witnessed it: he could scarcely help thinking that there was something supernatural in the appearance of one of these fine moths in a box in which he had put a cocoon of this kind, but in which he could not discover the slightest appearance of any insect having escaped from it, until he slit it longitudinally[666]. But from an observation of Meinecken, it appears that these converging threads serve[Pg 281] a double purpose; being necessary to compress the abdomen of the moth as it emerges from the cocoon, which forces the fluids to enter the nervures of the wings, and give them their proper expansion. For he found, that when the pupa is taken out of the cocoon, the moth is disclosed at the proper time, but remains always crippled in its wings; which never expand properly, unless the abdomen be compressed with the finger and thumb, so as to imitate the natural operation[667].

I am next to give you some account of the second mode in which the release of the perfect insect from its cocoon is effected—that, namely, wherein its own exertions chiefly accomplish the work. I shall from a large number select only a few instances. The texture of the cocoon of the silkworm-moth is uniform in every part, and the layers of silk are equally thick at both ends. The moth makes its way out by cutting or breaking these threads at the end opposite to its head: an operation which, as it destroys the continuity of the silk, those who breed these insects are particularly careful to guard against, by exposing the cocoon to heat sufficient to destroy the included pupa. The question is—What instruments does the moth employ to effect this? And this we are not able to answer satisfactorily. Malpighi asserts that the animal first wets the silk with a liquid calculated to dissolve the gum that connects the threads, and then employs its lengthened head to push them aside and make an opening[668]. But, as Reaumur has observed, besides that so obtuse a part as the head of a moth is but ill fitted to act as a wedge, we find[Pg 282] the threads not merely pushed to each side, but actually cut asunder. He therefore infers that the eyes, which are the only hard organs of the head, are the instruments by which the threads are divided—their numerous minute facets serving the purpose of a fine file[669]. It should be observed, however, that Mr. Swayne confirms Malpighi's assertion, that the silkworm does not cut, but merely pushes aside, the threads of its cocoon; and he informs us that he has proved the fact, by unwinding a pierced cocoon, the thread of which was entire[670]. Yet Reaumur's correctness cannot be suspected: and he affirms, that from observation there can scarcely be a doubt that most of the threads are broken[671]; which is further confirmed in an account of the breeding of silk-worms published in the American Philosophical Transactions: in which it is expressly stated, that cocoons out of which the fly has escaped, cannot be wound[672]. Analogy, it must be confessed, is against Reaumur's opinion; since other kinds of silkworms make their escape by means of a fluid. Thus we are informed by Dr. Roxburgh, that Attacus Paphia, when prepared to assume the imago, discharges from its mouth a large quantity of liquid, with which the upper end of the case is so perfectly softened, as to enable the moth to work its way out in a very short space of time,—an operation which, he says, is always performed in the night[673]. Perhaps the two opinions may be reconciled, by supposing the silkworm first to moisten and then break the threads of its cocoon. In those that are of a slighter texture, a mere push against the[Pg 283] moistened end is probably sufficient: and hence we find in so many newly disclosed moths the hair in that part wet, and closely pressed down[674]. If it be apparently difficult for the silkworm-moth to effect an opening in its cocoon, how much harder must seem the task of the puss-moth (Cerura Vinula) to pierce the solid walls of its wood-thickened case? Here the eyes are clearly incompetent; nor could any ordinary fluid assist their operation, for the gum which unites the ligneous particles is indissoluble in aqueous menstrua. You begin to tremble for the fate of the moth incarcerated in such an impervious dungeon—but without cause: what an aqueous solvent cannot effect, an acid is competent to: and with a bag of such acid our moth is furnished. The contents of this she pours out as soon as she has forced her head through the skin of the chrysalis, and upon the opposite end of the cocoon. The acid instantly acts upon the gum, loosens the cohesion of the grains of wood, and a very gentle effort suffices to push down what was a minute ago so strong a barrier. How admirable and effectual a provision! But there is yet another marvel connected with it. Ask a chemist, of what materials a vessel ought to be to contain so potent an acid: he will reply,—of glass. Yet our moth has no glass recipient: her bottle is a membranous bag; but of so wonderful a fabric as not to be acted upon by a menstruum which a gum, apparently of a resinous nature, is unable to resist! This fact can only be explained by the analogous insensibility of the stomach to the gastric juice, which in some animals can dissolve bone,—and it is equally worthy of[Pg 284] admiration. In both cases, the vitality of the membranous or fleshy receptacle secures it from the action of the included fluid; but how—who shall explain?

Ordinarily it is the moth that breaks the cocoon; but in the goat-moth and many Tortrices it is the pupa itself that performs the work, either wholly or partially. The pupa of the former is for this purpose furnished with sharp points upon the head, capable of effecting this object[675]. The locust-moth, another species of Cossus (C. Robiniæ Peck), whose history has been admirably detailed by Professor Peck, has a different process. "In the silk-moth," says he, "and all others which I have had opportunity to observe, the chrysalis bursts in the cocoon, and the fluid which surrounded the new insect in it escaping at the same time, so weakens or dissolves the fibre and texture of the silk, that the moth is able to extricate itself, leaving the chrysalis behind it; but this is not the manner in the locust-moth. After remaining till all its parts are fully grown and it is ready to quit its prison, a certain quantity of exercise is necessary, to break the ligaments which attach the moth to the shell of the chrysalis, and to loosen the folds of the abdomen. In taking this exercise, it can only move the abdomen in various directions: as one side of the rings is moved forward, the hooks in the serrated lines above mentioned (the adminicula) take hold of the silk, and prevent their sliding back; the next flexure brings forward the opposite side of the rings, which are prevented by the points on that side from slipping back in the same manner, and the chrysalis is forced out of the slightly woven extremity[Pg 285] of the cocoon, and through the silk-lined cavity, till it is protruded for about one-third of its length out of the opening in the bark, and into the air[676]."

An exception to the general rule—that the rupturing of the cocoon is the business of the inclosed insect itself—is met with amongst ants; the workers of which not only feed the young, but actually make an aperture in their cocoons, cutting the threads with their mandibles with admirable dexterity and patience, one by one, at the time they are ready to emerge, the precise period for which these indefatigable nurses are well aware of, that they may meet with no obstacle. Without this aid, the young ant would be unable to force its way through the strong and dense coating of silk that infolds it[677]. And a proceeding somewhat akin to this was observed by the Hon. Captain Percy, R.N., who himself related it to me. Being fond of the study of insects, he was in the habit of attending to their motions; and in the beginning of September 1821 noticed those of a number of female Tipulæ, probably T. oleracea L., busily engaged in depositing their eggs amongst the roots of grass. While observing these proceedings, he at the same time saw one quitting its pupa-case, which had already by its own efforts got its head, thorax, and anterior legs out of it. It was then joined by two male flies; which, with their anal forceps and posterior legs taking hold of the pupa-case, appeared with their mouths and anterior legs to push the little prisoner upwards, moving her backwards and forwards; and as they kept raising her, shifting their hold of the[Pg 286] skin till she was entirely extricated, when they left her to recover her strength by herself. Probably the extreme length of the two pair of hind-legs of these animals may render such assistance necessary for their extrication.

There remains yet to be explained under this head the manner in which the perfect insect is excluded from certain aquatic pupæ; such as those of Phryganeæ, gnats, and one of those Tipulidæ that resemble gnats. These pupæ (perhaps that they may be safe from the attack of birds) are destined to remain during the greater part of their existence in this state at the bottom of the water. But it is obvious that if the perfect insects were there to be disclosed, their wings would be wetted, and they would be drowned. It is the provision by which this result is obviated that now calls for your attention.

You have already been told that the larvæ of Phryganeæ inclose themselves in cases of different materials, open at each end[678]. You have also learned, that in becoming pupæ, they secure each end of their cases with a grating of silk[679]. When that change has occurred, they remain motionless at the bottom of the water. Now how are these pupæ, encased in tubes of a greater specific gravity than the surrounding fluid, to make their way to the surface when the time has arrived for their becoming denizens of the air? This they accomplish in the following manner:—The pupa is furnished with two strong exterior moveable mandibuliform processes, and has the power of moving its four anterior legs and antennæ while in the pupa-case. With these temporary jaws it makes an opening in one of the silken doors of its case, forces its[Pg 287] way out at that end, and then by moving its legs, the cases of which in some species are ciliated for this very purpose, swims to the surface, where its skin splits, and discloses the included insect. That these jaws are given for the express and exclusive purpose of being thus applied, seems undeniable. The pupa eats nothing—they are therefore in every other point of view superfluous. They are given to it alone of all other similar pupæ, because unnecessary to all others; and they are cast off along with the rest of the puparium, the perfect insect having no vestige of jaws[680].

The gnat has to undergo its change on the surface of the water—How is it to accomplish this without being wetted? In the pupa state they usually remain suspended with the posterior end of the body turned downwards: but when the period for its change is arrived, it stretches it out upon the surface, above which its thorax is elevated. Scarcely has it been a moment in this position, than, swelling out the interior and anterior parts of the thorax, it causes it to split between the two respiratory horns. Through this opening the anterior part of the gnat then emerges. As soon as the head and trunk are disengaged, it proceeds with its labour, and gets out more and more; elevating itself so as to appear in the puparium like a mast in a boat. As it proceeds, the mast is more and more elevated and lengthened, till it becomes nearly perpendicular—just as the mast of a boat is gradually raised from a nearly horizontal to a vertical position: at this period a very small portion of the abdomen remains in the puparium. Neither its legs nor wings are of any use[Pg 288] in maintaining it in this position. The latter are too soft, and, as it were, folded; and the former are stretched out along the abdomen—the segments of this last part are the only agents. The observer who sees how the little boat gradually sinks, and how its margin approaches the water, forgets the mischievous insect it contains, which at another time he would crush without remorse, and becomes interested for its fate; especially should wind agitate the water. A very little is sufficient to drive about rapidly the little voyager, since it catches the wind in some degree as a sail. If it should be upset, it would be all over with it;—and numbers do thus perish. The gnat, after having fixed itself thus perpendicularly, draws first its two anterior legs out of their case, and moves them forward, and next the two intermediate ones; then inclining itself towards the water, it rests its legs upon it, for water is to them a soil sufficiently firm and solid to support them, although surcharged with the weight of the insect's body. As soon as it is thus upon the water, it is in safety; its wings unfold themselves and are dried, and it flies away. All this is the work of an instant[681].

The pupæ of Chironomus plumosus proceed from those red worm-like larvæ so common throughout the summer in tubs of rain-water, &c., described by Reaumur[682]. They are not inclosed in cases, but are of a greater specific gravity than the water at the bottom of which they reside, until within a few hours of the exclusion of the fly. They have the power of swimming, however; and by moving the tail alternately backwards and forwards, can slowly raise themselves to the top of the water. But[Pg 289] here occurs a difficulty. For the extrication of the imago it is necessary that they should remain quietly suspended at the surface; and moreover that the thorax, in which the opening for its exit is to be made, should be at least level with it: and this is precisely what takes place. If you watch one of these pupæ when it ascends from the bottom, you will see that as soon as it has reached the top it remains suspended there motionless; and that its thorax is the highest part of the body, and level with the surface. Now the question is, in what way this is accomplished? How can a pupa of greater specific gravity than water, remain suspended without motion at its surface? and how can its thorax, which is at its heaviest end, be kept uppermost?—By a most singular and beautiful contrivance, which I shall explain; the more particularly because it has escaped Reaumur, and, as far as I know, all other entomological observers. The middle of the back of the thorax has the property of repelling water—apparently from being covered with some oily secretion. Hence, as soon as the pupa has once forced this part of its body above the surface, the water is seen to retreat from it on all sides, leaving an oval space in the disk, which is quite dry. Now though the specific gravity of the pupa is greater than that of water, it is but so very slightly greater, that the mere attraction of the air to the dry part of the thorax, when once exposed to it, is sufficient to retain it at the surface; just as a small dry needle swims under similar circumstances. That this is a true solution of the phænomenon, I am convinced by the result of several experiments. If, when the pupa is suspended at the surface, a drop of water be let fall upon the dry portion of the thorax, it instantly sinks to the[Pg 290] bottom,—the thorax, which belongs to the heaviest half, being the lowest; and if the pupa be again brought to the surface, so that the fluid is repelled from its disk, it remains suspended there without effort, as before. Just previously to the exclusion of the fly, the dry part of the thorax is seen to split in the middle. The air enters, and forms a brilliant stratum resembling quicksilver, between the body of the insect and its puparium; and the former pushing forth its head and forelegs, like the gnat, rests the latter upon the water, and in a few seconds extricates itself wholly from its envelope.

Before I close this letter, I must state a fact connected with the subject of it that deserves to be recorded. It is a general rule, that one pupa-case incloses only one insect; but Kleesius, a German entomologist, asserts that he had once two specimens of Gastropacha quercifolia produced from one pupa; which was large, being full two inches long, and one thick.

[Pg 291]

LETTER XXXII.

STATES OF INSECTS.

IMAGO STATE.

When the insect has quitted the exuviæ of the pupa, it has attained the last stage of its existence. It is now termed an Imago, or perfect insect; and is capable of propagation.

Just after its exclusion, it is weak, soft, and languid: all its parts are covered with moisture; and, if a winged insect, its wings have so little the appearance, either in shape, size, or colour, which they are about to assume, that it might be taken for a mutilated abortion, rather than an animal in the most vigorous stage of life. If it be a beetle, its elytra, instead of covering the back of the abdomen, are folded over the breast: their substance is soft and leathery, and their white colour exhibits no traces of the several tints which are to adorn them. If the insect be a butterfly or a moth, the wings, instead of being of their subsequent amplitude, and variegated and painted with a variety of hues and markings, are in large species scarcely bigger than the little finger nail, falling over the sides of the trunk, and of a dull muddy colour, in which no distinct characters can be traced.[Pg 292] If the excluded insect be a bee or a fly, its whole skin is white and looks fleshy, and quite unlike the coloured hairy crust which it will turn to in an hour or two; and the wings, instead of being a thin, transparent, expanded film, are contracted into a thick, opaque, wrinkled mass.

These symptoms of debility and imperfection, however, in most cases speedily vanish. The insect, fixing itself on the spoils of the pupa, or some other convenient neighbouring support, first stretches out one organ, and then another: the moisture of its skin evaporates, the texture becomes firm, the colours come forth in all their beauty; the hairs and scales assume their natural position; and the wings expanding, extend often to five or six times their former size—exhibiting, as if by magic, either the thin transparent membranes of the bee or fly, or the painted and scaly films of the butterfly or moth, or the coloured shells of the beetle. The proceedings here described I witnessed very recently with regard to a very interesting and beautiful butterfly, the only one of its description that Britain has yet been ascertained to produce—I mean Papilio Machaon. The pupa of this being brought to me by a friend early in May this year (1822), on the sixteenth of that month I had the pleasure to see it leave its puparium. With great care I placed it upon my arm, where it kept pacing about for the space of more than an hour; when all its parts appearing consolidated and developed, and the animal perfect in beauty, I secured it, though not without great reluctance, for my cabinet—it being the only living specimen of this fine fly I had ever seen. To observe how gradual, and yet how rapid, was the development of the parts and organs, and[Pg 293] particularly of the wings, and the perfect coming forth of the colours and spots, as the sun gave vigour to it, was a most interesting spectacle. At first it was unable to elevate or even move its wings; but in proportion as the aërial or other fluid was forced by the motions of its trunk into their nervures, their numerous corrugations and folds gradually yielded to the action, till they had gained their greatest extent, and the film between all the nervures became tense. The ocelli, and spots and bars, which appeared at first as but germes or rudiments of what they were to be, grew with the growing wing, and shone forth upon its complete expansion in full magnitude and beauty.

To understand more clearly the cause of this rapid expansion and development of the wings, I have before explained to you that these organs, though often exceedingly thin, are always composed of two membranes, having most commonly a number of hollow vessels, miscalled nerves, running between them[683]. These tubes, which, after the French Entomologists, I would name nervures, contribute as well to the development of the wings, as to their subsequent tension. In the pupa, and commonly afterwards, the two membranes composing the organs in question do not touch each other's inner surface, as they afterwards do: there is consequently a space between them; and being moist, and corrugated into a vast number of folds like those of a fan, but transverse as well as longitudinal, and so minute as to be imperceptible to the naked eye, the wings appear much thicker than in the end. Now as soon as the insect is disclosed, a fluid enters[Pg 294] the tubes, and being impelled into their minutest ramifications, necessarily expands their folds; for the nervures themselves are folded, and as they gradually extend in length with them, the moist membranes attached to them are also unfolded and extended. In proportion as this takes place, the expanding membranes approach each other, and at last, being dried by the action of the atmosphere, become one. To promote this motion of the fluid, seems the object of the agitations which the animal from time to time gives to its unexpanded wings. That a kind of circulation, or rather an injection of an aqueous fluid into these organs, actually takes place, may be ascertained by a very simple experiment. If you clip the wings of a butterfly during the process of expansion, you will see that the nervures are not only hollow, but that, however dry and empty they may subsequently be found, they at that time actually contain such a fluid[684]. Swammerdam, who appears to have been the first physiologist that paid attention to this subject, was of opinion that an aëriform as well as an aquiform fluid contributes to produce the effect we are considering. He had observed that, if a small portion be cut off from the wing of a bee, a fluid of the latter kind exuded from its vessels in the form of pellucid globules, becoming insensibly drops—which he concluded proved the action of the latter; and he noticed, also, that the wings were furnished with tracheæ, which were at that time distended by the injected air; whence he justly surmised, that the action of the air was also of great importance to produce the expansion of the wing[685]. And Jurine found that every nervure contains[Pg 295] a trachea, which, proceeding from the interior of the trunk in a serpentine direction, follows all the ramification of the nervure, though it does not fill it[686]. Though Reaumur attributes the expansion of the wings chiefly to an aqueous fluid, yet he suspects that the air on some occasions contributed to it[687].

The wings of the other tribes of insects probably differ from the Lepidoptera in the manner in which they are folded. It should seem from Reaumur's description, that those of some flies, instead of the straight transverse folds of the former, have angular or zigzag folds[688]; which equally shorten the wing. Many Hymenoptera have wings without any nervures except the marginal. We may conjecture that these are more simply folded, so as to render their expansion more easy; but even in these wings there are often tracheæ, which appear as spurious nervures, and help to effect the purpose we are considering.

The operation of expanding their wings, in by far the larger number of insects, takes place gradually as described above; and, according to their size, is ended in five, ten, or fifteen minutes; in some butterflies half an[Pg 296] hour, in some even an hour. A few species, such as Sphinx Œnotheræ F., require several hours, or even a day, for this operation; and, from the distance to which they creep before it has taken place, a considerable degree of motion seems requisite for causing the necessary impulse of the expanding fluids[689]. In a few genera, however, as the gnat, the gnat-like Tipulidæ, and the Ephemeræ, this process is so rapid and instantaneous, that the wings are scarcely disengaged from the wing-cases before they are fully expanded and fit for flying. These genera quit the pupa at the surface of the water, from which, after resting upon it for a few moments, they take flight: but this would evidently be impracticable, and immersion in the fluid, and consequent death, would result, were not the general rule in their case deviated from.

Some species of the last of these genera, Ephemera, are distinguished by another peculiarity, unparalleled, as far as is known, in the rest of the insect world. After being released from the puparium, and making use of their expanded wings for flight, often to a considerable distance, they have yet to undergo another metamorphosis. They fix themselves by their claws in a vertical position upon some object, and withdraw every part of the body, even the legs and wings, from a thin pellicle which has inclosed them, as a glove does the fingers; and so exactly do the exuviæ, which remain attached to the spot where the Ephemera disrobed itself, retain their former figure, that I have more than once at first sight mistaken them for the perfect insect. You can conceive without difficulty how the body, and even legs, can be withdrawn[Pg 297] from their cases; but you must be puzzled to conjecture how the wings, which seem as thin, as much expanded, and as rigid as those of a fly, can admit of having any sheath stripped from them; much less how they can be withdrawn, as they are, through a small opening at the base of the sheath. The fact seems to be, that though the outer covering is rigid, the wing inclosed in it, notwithstanding it is sometimes more than twenty-four hours before the change ensues, is kept moist and pliable. In proportion, therefore, as the insect disengages itself from the anterior part of the skin, the interior or real wings become contracted by a number of plaits into a form nearly cylindrical, which readily admits of their being pulled through the opening lately mentioned; and as soon as the insect is released from its envelope, the plaits unfold, and the wing returns to its former shape and dimensions. Thus our little animal, having bid adieu to its shirt and drawers, becomes, but in a very harmless sense, a genuine descamisado and sansculotte. It does not seem improbable, that the pellicle we have been speaking of is analogous to that which, in addition to the outer skin, incloses the limbs of Lepidoptera, &c. in the pupa state, but which they cast at the same time with the puparium, and leave adhering to it[690].

The body of newly-disclosed insects commonly appears at first of its full size; but the aphidivorous flies (Syrphus F. &c.), and some others, in about a quarter of an hour after leaving the pupa become at least twice as large as they were at their first appearance: this apparent sudden growth, which is also noticed by Goedart,[Pg 298] Reaumur found to depend upon the expansion of the previously compressed segments of the animal by means of the included air[691]. Both in this instance and in that of insects whose wings only require expansion, the size of the imago often so greatly exceeds that of the pupa, that we can scarcely believe our eyes that it should have been included in so contracted a space. The pupa of one of the beautiful lace-winged flies (Hemerobius Perla) is not so big as a small pea, yet the body of the fly is nearly half an inch long, and covers, when its wings and antennæ are expanded, a surface of an inch square[692].

When the development of the perfect insect is complete, and all its parts and organs have attained the requisite firmness and solidity[693], it immediately begins to exercise them in their intended functions; it walks, runs, or flies in search of food; or of the other sex of its own species, if it be a male, that it may fulfill the great end of its existence in this state—the propagation of its kind. Previously to thus launching into the wide world, or at least immediately afterwards, almost all insects discharge from their intestines some drops of an excrementitious fluid, often transparent, and sometimes red. I have before related to you the alarm that this last circumstance has now and then produced on the minds of the ignorant and superstitious[694]. Whether this excrement[Pg 299] is produced indifferently both by males and females I cannot positively assert; but a circumstance related by Jurine affords some ground for a suspicion that it is peculiar to the latter. A specimen of a female of Lasiocampa Rubi, when killed emitted some of this fluid, which dropped upon the floor: this appeared to attract the males to the apartment in which it happened, and to the very spot—from whence it may be conjectured, that the scent of the fluid brought them there, and that the use of it is to bring the sexes together soon after exclusion from the pupa[695].

The colour, sculpture, and other peculiarities which distinguish insects in this state I shall consider at large in another letter, when I treat of their external parts and organs. Under the present head I shall confine myself to pointing out the characters by which the sexes of many species are distinguished from each other; as likewise the duration of their life in their perfect state; together with the circumstances on which this duration depends.

I. Sexual Distinctions. The first general rule that may be laid down under this section is,—That among insects, contrary to what mostly occurs in vertebrate animals, the size of the female is almost constantly larger than that of the male. Even in the larva and pupa states, a practised eye can judge, from their greater size, which individuals will become females. There are, however, some exceptions to this rule. Thus amongst the Coleoptera, the male Dynastidæ, remarkable for their horns,[Pg 300] as you may see in D. Alocus, Antæus, Actæon, &c., as likewise those of Lucanus, are larger than the unarmed females[696]. In the Neuroptera the female Libellulidæ are sometimes sensibly smaller, and never larger, than their males[697]. In the Hymenoptera the male of the hive-bee, but more particularly that of Anthidium manicatum and other bees of that genus, is much more robust than the other sex[698]. In the Diptera, the same difference is observable in Syrphus Ribesii, and some other aphidivorous flies, and also in Scatophaga stercoraria[699]. And amongst the apterous tribes, we are informed by De Geer that the male of Argyroneta aquatica, which builds an aërial palace in the bosom of the waters[700], usually exceeds the female in bulk[701]. The reason of this rule seems in some degree connected with the office of the female as a mother, that sufficient space may be allowed for the vast number of eggs she is destined to produce; and it is when impregnation has taken place, and the eggs are ready for extrusion, that the difference is most sensible. In the majority of cases this sexual disproportion is not very considerable, but in some few it is enormous. Reaumur mentions a beetle, of which he intended to give the history, the male of which is so small compared with the female, that a bull not bigger than a sheep, or even a hare, set by the side of the largest cow, would aptly contrast with them. This little beetle, he says, has wings[Pg 301] and elytra, while the giant female has no vestige of either, having the upper surface of its body naked and membranous[702]. The species to which this illustrious Naturalist here alludes, does not appear to have been ascertained. The female of many gall-insects (Cocci) is so large in comparison with the male, that the latter traverses her back as an ample area for a walk[703]. But this is nothing compared with the prodigious difference between the sexes of Termes fatale, and other species of white ants, whose males are often many thousand times less than the females, when the latter are distended with eggs[704]. Accidental differences in the size of the sexes sometimes arise: as when the female larva has, from any cause, been deprived of its proper supply of food, it will occasionally be less than the male. De Geer has stated a circumstance with respect to the Aphides that produce galls, that should be mentioned under this head—the first, or mother female, is larger than any of her progeny ever become[705].

The second observation that may be generally applied to the sexes of insects is, that, size excepted, there is a close resemblance between them in other respects. But to this rule the exceptions are very numerous, and so important that it is necessary to specify examples of each under distinct heads.

i. In some species the sexes are either partly or wholly of a different colour. Thus, in the order Coleoptera, the elytra of the male of Rhagium meridianum F. are testaceous, and those of the female black. Leptura rubra of[Pg 302] Linné, with red elytra, is the female of his L. testacea, in which they are testaceous. Cantharis dermestoides of the same author is the other sex of his Meloe Marci; one of which is chiefly testaceous, and the other black: which seems to have so misled Linné, that he placed them in different genera. One more instance in this order, the female of Cicindela campestris, as was first observed to me by our friend Sheppard, has a black dot on each elytrum, not far from its base near the suture, which the male has not.

Amongst the Orthoptera, the male Locustæ F., as Professor Lichtenstein has informed us[706], have a fenestrated ocellus, which is not to be found in the other sex. I was once attending to the proceedings of a Hemipterous species, Pentatoma oleracea Latr., which I found in union: the paired insects had white spots, but another individual was standing by them, in which the spots were of a sanguine hue. I mention this by the way only—the spots in the prolific sexes being of the same colour: but might not the red spotted one be a neuter?

The sexes of many Lepidoptera likewise differ in their colour. I must single out a few from a great number of instances. The males of Lycæna Argus F. have the upper surface of their anterior wings of a dark blue, while in the female it is wholly brown. The wings of the former sex of Hypogymna dispar are gray, clouded with brown; but those of the latter are white, with black spots. In the brimstone butterfly (Colias Rhamni), which is one of the first that appear in the spring, the wings of the male are yellow—of the female whitish. In the common[Pg 303] orange-tip (Pieris Cardamines F.), one sex has not the orange tip to the upper wings: and, to name no more, the male of Lycæna dispar, one of our rarest and most beautiful butterflies, has only a single black spot in the disk of its fulgid wings; while in the other sex, the primary pair have nine, and the secondary are black, with a transverse orange fascia near the posterior margin. But the most remarkable difference in this respect observable in the insects of the order in question, takes place in a tribe, of which only one species is certainly known to inhabit Britain—I mean the Papiliones Equites of Linné: what he has called his Trojani and Achivi in some instances have proved only different sexes of the same species. Mr. MacLeay's rich cabinet affords a singular instance confirming this assertion;—a specimen of a Papilio is divided longitudinally, the right hand side being male, and the left hand female. The former belongs to P. Polycaon, a Grecian, the latter to P. Laodocus, a Trojan. An instance of two Grecians thus united is recorded in the Encyclopédie Méthodique, as exhibited in a specimen preserved in the Museum of Natural History at Paris; which on the right hand side is P. Ulysses, on the left P. Diomedes[707].

In the Neuroptera, the Libellulidæ are remarkable for the differences of colour in the sexes. In the common Libellula depressa, which you may see hawking over every pool, the abdomen of the male is usually slate-colour, while that of his partner is yellow, but with darker side-spots. Reaumur, however, noticed some males that were of the same colour with the females[708]. Schelver[Pg 304] observed, when he put the skins of Libellula depressa into water, that the colours common to both sexes were in the substance of the skin, and remained fixed; while those that were peculiar to one could be taken off with a hair-pencil, and coloured the water: which therefore were superficial, and, as it were, laid on[709]. The yellow males, therefore, that Reaumur observed, were probably such as had the superficial blue colour which distinguishes them washed off. In Calepteryx Virgo Leach, the former are of a lovely silky blue, and the latter green. In Agrions F. nature sports infinitely in the colours of the sexes.

In the order Hymenoptera there are often differences equally great; the sexes of many of the Ichneumons and Saw-flies are of quite different colours. The former tribe Linné has divided into sections, from the white annulus observable in the antennæ of some, and from the colour of their scutellum: but these are often merely sexual characters[710]. The male of Anthophora retusa Latr., a kind of wild bee, is wholly black, the female wholly gray, and of so very different an aspect that they were long regarded as distinct species; a mistake which has likewise occurred with regard to the sexes of Osmia cærulescens, another bee, of which the male has a bronzed and the female a violet abdomen[711]. The nose of male Andrenæ Latr. is often yellow, or white, as in A. hæmorrhoidalis—when that of the female is black[712]. The labrum also is often of a different colour in the sexes, as in Ceratina Latr.

[Pg 305]

In the Diptera, Aptera, Arachnida, &c., I am not aware of any striking difference in the colours of the sexes.

ii. The sexes of insects vary (but more rarely than in colour) in their sculpture also, and pubescence. Thus the elytra of the females of many of the larger water-beetles (Dytiscus) are deeply furrowed, while those of the males are quite smooth and level[713]. The thorax of the female in several species of Colymbetes of the same tribe, as C. Hybneri and transversalis, on each side has several tortuous impressed lines or scratches, like net-work, which are not to be discovered in the male. Hyphydrus gibbus Latr., which differs solely from H. ovalis (Dytiscus ovalis Illig.) in being thickly covered with minute impressed puncta, is, from the observation of the Rev. R. Sheppard, the other sex of this last, with which he has taken it coupled; and it is by no means improbable that Hydroporus picipes (Dytiscus punctatus Marsh.) and H. lineatus,—between which, as Gyllenhal has justly observed, the same difference only exists,—are in like manner sexual varieties. With respect to pubescence, I have not much to say. Another aquatic beetle, Acilius sulcatus Leach, has not only its elytra sulcated, but the furrows of these, and a transverse one of the thorax, are thickly set with hair; while the male is smooth, and quite naked. Particular care seems to have been taken by the Creator, that when all the above inhabitants of the water are paired, the male should be able to fix himself so firmly, by means[Pg 306] of his remarkable anterior tarsi, (which I shall afterwards describe,) and these asperities, &c. in the upper surface of his mate, as not to be displaced by the fluctuations of that element, the reluctance of the coy female, or any other slighter cause.

In a moth called the ghost (Hepialus Humuli), the posterior tibia of the male is densely bearded, but not of the female[714].—Some Hymenoptera, as Ammophila Kirb. and Stigmus Jurine, have the upper lip of the male clothed with silver pile, while that of the female is not so ornamented. The legs of some bees are distinguished in the sexes by a difference in their clothing. That observable in those of the hive-bee has been before noticed[715]. In Andrena of Latreille[716] the posterior tibia of the female is covered externally with a dense brush of hairs, for collecting the pollen; and the posterior legs at their base have a curled lock of hair—which are not to be found in the male[717]. In Dasypoda, Melecta, Anthophora, Centris, Epicharis, &c. of the same author, the first joint of the tarsus of the female, and in Xylocopa almost the whole tarsus, is also similarly signalized from that of the other sex. In Bombus, as in the hive-bee, the posterior tibiæ of the females and neuters are furnished with a basket of hairs for carrying their pollen paste, which you will in vain look for in the male[718]. The latter, however, in some species of this tribe are distinguished from the former by the longer hairs of their legs, but not in the posterior ones. Thus, in Anthophora retusa the first joints of the[Pg 307] intermediate tarsus are bearded internally with a thin fringe of long hairs, and the first externally with a triangular one of short ones at the apex: but what is most remarkable, the last or unguicular joint, which in almost every other bee is naked, is on both sides fringed with long hairs[719]. In that remarkable genus Acanthopus Illig., of which the male only is known, the first and last joint of the intermediate tarsus have a dense external brush of stiff hairs, which probably is also a sexual character[720]. Another sexual kind of clothing is exhibited by the females of those bees that have their labrum or upper-lip inflexed (Megachile Latr.)[721]. Their abdomen is covered underneath with a brush of stiff hairs, involved in which they carry the pollen they collect. In the males of some of this tribe, as of M. Willughbiella, the first four joints of the anterior tarsus on their inner side have a long dense fringe of incurved hairs[722]: a circumstance also to be found in the same sex of Xylocopa latipes, in which the claw-joint also is bearded[723]. In Andrena Latr. the last dorsal segment of the abdomen of the same sex is fringed, while that of the male is naked[724]. In the humble-bees (Bombus), the mandibles of the male are bearded with curled hairs, while those of the females and neuters are without them. Some bees, as Andrena and Halictus Latr., have the anus of the female bearded, and that of the male naked: in some Bombyces the reverse takes place.

[Pg 308]

iii. With regard to the general shape of their body, the male and female usually resemble each other: but there are some exceptions to this rule. The male of the hive-bee is much thicker and more clumsy than either the female or the worker; but in Halictus Latr. the males are nearly cylindrical in shape, and very narrow; while the other sex are oblong or ovate, especially their abdomen: and in Andrena Latr. the former are much slenderer than the females, and of a more lanceolate shape. But a still more striking difference in this respect between the sexes is exhibited by some species of the genus Ptinus F., in which the male is long and slender, and the female short and thick. This, in more than one instance, has occasioned them to be mistaken for distinct insects: thus, P. Lichenum and P. similis, P. ovatus and P. testaceus, of Mr. Marsham, are mere sexual varieties. But the most entire abalienation of shape at present known, is that which distinguishes the male from the female Coccus; these are so completely dissimilar as scarcely to have any part in common. In Bombyx vestita F., and others of the same family, while the males are of the ordinary conformation of the order, the females are without even the slightest rudiments of wings; they have no antennæ, the legs are extremely short, not longer than those of the caterpillar; and the body is entirely destitute of scales, so that they altogether assume the exact appearance of hexapod larvæ[725]. A conformation nearly similar takes place in the female of Tinea Lichenella; but in this the feet are longer, and the anus is furnished with a long retractile ovipositor[726].

[Pg 309]

iv. In many cases, the structure of particular parts and organs of the body differs in the sexes. As the facts connected with this part of our present subject are extremely numerous and various, it will be convenient to subdivide it, and consider the sexual characters that distinguish—the Head, Trunk, and Abdomen of insects, and their several appendages.

1. The Head. This part in some females is considerably larger than it is in the male. This is the case with the ants, and several other Hymenoptera; while in some Andrenæ, as A. hæmorrhoidalis, and Staphylinidæ, as St. olens, that of the male is the largest. But in none is the difference more conspicuous than in the stag-beetle (Lucanus); in which genus the male not only exceeds the female in the length of his mandibles, but also greatly in the size and dimensions of his head. In the Apion genus, the rostrum of the female is generally longer and slenderer than that of her mate; and in Brentus, the rostrum of one sex (probably the male) is long and filiform, while in the other it is thick and short. This is particularly visible in B. dispar and maxillosus[727], &c.

One of the most striking distinctions of the males in this part of their body, are those threatening horns, usually hollow, with which the heads of many of the male lamellicorn insects and some others are armed, and which give them some resemblance to many of the larger quadrupeds. Many are unicorns, and have their head armed with only a single horn; which in some, as in Oryctes Illig., Dynastes Endymion[728], &c. is very short; in others,[Pg 310] very long, as in Dynastes Enema, Pan, Elephas[729]. In one, again, it is thick and robust; as in the clumsy Dynastes Actæon[730]: in another very slender, as in Onthophagus spinifer[731]. With respect to its direction in Elephastomus proboscideus MacLeay, it is horizontal[732] and straight; in Phaleria cornuta horizontal and broken, or the apex turning outwards and forming an angle with the base[733]; in Dynastes Hercules horizontal, and recurved at the apex[734]; in D. Actæon, Elephas, and Typhon, recurving from the base. In Geotrupes dispar it is recurved, so that its point exactly coincides with that of the porrected thoracic horn, with which it forms a kind of forceps[735]. In Copris lunaris F. and Diaperis horrida, the horn is nearly upright[736]. In Onthophagus Xiphias it is dilated at the base, and reclining upon the thorax; and at the apex attenuated, and bending forwards, or nodding. In Passalus cornutus it rises a little, and then bends wholly forwards. In Dynastes Milon, a most remarkable beetle, it slopes backwards in a waving line[737]; and in Onthophagus spinifer it is recurved and reclining.—In speaking of the direction of the horn, you must recollect that it will vary in proportion as the head varies from a horizontal position: so that an upright horn will become inclined or reclined, as the head bends forwards or backwards; but I speak of it as it appears when the head is horizontal.[Pg 311] Again, it varies in its teeth or branches. In Dynastes Hercules it is armed with several teeth. In D. Elephas and Actæon it has only one large one at its upper base[738]. In D. Milon it is serrated above. In D. Alcides, Tityus, Ægeon, Copris lunaris, &c. the horn is unarmed and simple at the apex. In D. Oromedon, Gedeon, Enema, Actæon and congeners, it is bifid. In some the horn is at first a broad lamina or ridge, which terminates in two branches, as in Onthophagus Vacca. In this the branches are straight; but in another undescribed species in my cabinet (O. Aries Kirby, MS.) they are first bent inwards, and then at the apex a little recurved: and in D. dichotomus it is divided into two short branches, each of which is bifid[739]. Other males emulate the bull, the he-goat, or the stag, in having a pair of horns on their head. In Onthophagus Taurus, these arms in their curvature exactly resemble those of the first of these animals[740]. In Goliathus pulverulentus, the straight, robust, diverging, sharp horns are not unlike those of some of the goat or gazel tribe. I have a beautiful little specimen in my cabinet, (I believe collected by Mr. Abbott of Georgia,) in which the horns have a lateral tooth, or short branch, like those of a stag; and which I have therefore named O. cervicornis. In O. Vacca, Camelus, &c. the horns are very short, and nearly perpendicular. In the male of[Pg 312] Copris Midas, the two longer perpendicular horns have a deep cavity between them, which, together with its black colour, give it a most demoniac aspect; so that you would think it more aptly representative of a Beelzebub or Beelzebul than a Midas[741], or than Phanæus Beelzebul MacL. A similar cavity is between the occipital horns of Diaperis hæmorrhoidalis Payk. Some species of Rynchænus, as R. Taurus, have a pair of long horns upon the rostrum of the male, the rudiments only of which are to be traced in the female[742]. Other species go beyond any known quadrupeds in the number of horns that arm their heads. Thus Ditomus calydonius Bonelli, belonging to Carabus L., has three equal horns[743]. The same number distinguishes Onthophagus Bonasus; but the intermediate one is very short. In Goliathus Polyphemus the middle horn, on the contrary, is much longer and thicker than the lateral ones, and forked at the apex; so that it looks as if it had four of these weapons[744]. A little Diaperis (D. viridipennis F.), a native of Carolina, has four horns upon the head of the male; namely, two long ones on the occiput, and two short dentiform ones on the nose. In a species nearly related to this, sent me by Professor Peck from New England, there is a cavity between the two occipital horns. The same number distinguishes Onthophagus quadricornis (Copris F.). The situation also of the horns varies: In some it is in the middle of the head, as Oryctes nasicornis, Copris lunaris, &c.: in others, as in Onthophagus nuchicornis, Xiphias, &c. it is a process[Pg 313] of the occiput or hind-head; and in O. Oryx F. the two horns proceed from the anterior part of the head. In the other sex, in insects the head of whose males is armed with horns, they are usually replaced by mere tubercles, or very short elevations, as you may see in the female of Copris lunaris; or by transverse ridges, as in the Onthophagi: or else the head is without arms, and quite smooth, as in Diaperis, Phaleria, &c. What may be the use of these extraordinary appendages, as well as those on the thorax, and in some cases on the abdomen, (which I shall mention afterwards), to the males, has not yet been ascertained. Whether the individuals of this sex are more exposed to the attack of birds and other enemies, in consequence of being more on the wing than the females, and are therefore thus provided with numerous projecting points for defence, is a question worth considering[745]. It is the only probable conjecture on the cui bono of these arms that I can at present make. Under this head I ought to notice the remarkable membranous process of an obovate shape, which like an umbrella covers the head of Acheta umbraculata F.[746] Whether the sharp curved horns which arm this part in another Acheta figured by Stoll[747], in an incumbent posture, with their point towards the mouth, are a sexual distinction, we are not informed,—probably they are.

The organs of the head also present many sexual[Pg 314] distinctions. The upper lip (labrum) in Halictus Latr., a tribe of wild bees, in the female is furnished with an inflexed appendage, which is not discoverable in that of the male[748]; and the shape of this lip in Sphecodes Latr. differs in the sexes[749]. Perhaps the horn or tubercle observable on this part of some female Nomadæ F.[750] may be wanting in the male.

The under-lip (labium)—taken in a restricted sense for that central part from which emerge the labial palpi, and which is often considered as the mentum,—does not offer any striking variations in the sexes. One, however, is of importance, as it helps to prove which are the true female Lucani. In the male the labium is emarginate, in the female it is intire. This may be seen both in L. Cervus and femoratus, and probably in other species. The sculpture also is different, the lip being smooth in the former and covered with excavated puncta in the latter. The tongue (lingua or ligula) of the sexes is usually the same; except in the hive-bee, in which that of the neuters is longer than that of the male and female.

The upper-jaws (mandibulæ), however, often afford striking sexual characters. The enormous protended ones of the common stag-beetle (Lucanus Cervus) attract the attention of the most incurious observer; and these are now generally allowed to be of this description. Geoffroy and Mr. Marsham, indeed, have asserted that they have taken in coitu those with long mandibles: but as these males are pugnacious, and attack each other with great fury, as Mr. Sheppard informs me, it is not improbable that these gentlemen may have mistaken a battle[Pg 315] for an amour: since not only have those with long mandibles been often taken united with those that have short ones[751], but the same difference obtains in the sexes of other species. This is particularly observable in Lucanus femoratus, of which I received from Brazil many specimens agreeing in every respect except in this, that one had short and the other very long mandibles. These organs vary in different specimens, as to the number of their teeth and branches. They are singularly robust in L. Alces[752]; but in none more threatening than in L. Elephas[753], in which they curve outwards and downwards. In Mr. W. MacLeay's genus Pholidotus, they are almost parallel to each other, and curve downwards; in Lucanus nebulosus Kirby, they assume a contrary direction[754]; as they do likewise in Lamprima Latr.[755] In Lucanus Capreolus the points close over each other[756]. In Lethrus F. in the female, but not the male, the mandible is armed below with a long incurved horn. In Lucanus serricornis they form a complete forceps[757]. In Siagonium quadricorne Kirby[758] the mandible is furnished at its base with an exterior horn, which is probably a sexual distinction. The male of Synagris cornuta, a kind of wasp, is still more conspicuous in this respect; for from the upper side of the base of its straight slender mandibles proceed a pair of crooked, decurved, tortuous, sharp horns, not only longer than[Pg 316] the mandible, but than the head itself[759]. Many sexual differences are observable in the mandibles of the various tribes of bees (Anthophila Latr.). Thus, in Colletes Latr. the male mandible is more distinctly bidentate at the apex than the female[760]: in Sphecodes Latr. and others, the reverse of this takes place[761]. Where these organs in both sexes are toothed at the apex, they often vary in the number of teeth. Thus, the female of Megachile centuncularis Latr. has four teeth at the apex of its mandible, while the male has only two[762]. In M. Willughbiella, though the mandibles of both sexes have four teeth, yet those of the male are sharp, and the two external ones the longest; while those of his mate are obtuse, and all nearly equal in length[763]. In Anthidium manicatum Latr., the former has only three teeth, while the latter has five[764]. The differences in this respect in the hive-bee have been before noticed[765]; those of the humble-bees (Bombus Latr.) are strikingly distinguished from each other; the female mandible being very stout and wide, constricted in the middle, and furrowed on its outer surface; and the male, on the contrary, very slender at the apex, dilated at the base, and without furrows[766].

Of all the organs of the head, none seem so little subject to sexual variation as the under-jaws (maxillæ)[767]. I[Pg 317] can bring forward only one striking instance of it, and some degree of doubt rests even upon that. In the genus Nemognatha of Illiger, the maxillæ of the male are elongated, narrow, setiform, and often involute or spiral, like those of a bee or a butterfly. But that this is peculiar to the males is at present only surmised[768]. I possess several species of the genus, all of which are distinguished by long maxillæ; though in some they are as long as the body, and in others scarcely half that length. Gnathium Kirby is similarly characterized[769].

The maxillary palpi occasionally differ in the sexes. In Cerocoma those of the female are filiform, while the two intermediate joints of those of the other sex are much thicker than the first and the last[770]. In Hylæcetus and Lymexylon, those of the male are still more remarkable: they are pendent, the last joint very large, and laciniated so as to form a tuft[771]. The female ones grow gradually larger towards the end, but are not at all divided there[772]. The palpi of male spiders are of a very different structure from those of the other sex, terminating in a very complex incrassated piece, which has been supposed to contain the organ of generation; but this, according to Treviranus, is a mistaken idea—that organ being, as usual, to be found in the abdomen[773]. In the common gnat the palpi of the male are as long as the proboscis, consist of five joints, and at the end are tufted with hairs; while those of the female are scarcely one-fourth of its[Pg 318] length, have only three joints, and are not tufted. Whether the labial palpi in any genus differ in the sexes, I cannot affirm with certainty: I have not, however, observed any such variation in them.

I shall next mention some organs of the head, in which the difference between the sexes is often very striking and peculiar. You will readily conjecture that I am speaking of the antennæ. And here the advantage seems wholly on the side of the males: since in them these wonderful instruments of unknown sensations are not only more complex, but usually more elegant, than those of the other sex. You will pardon me, therefore, if I enlarge a little more than ordinary upon a subject so full of interest, and say something upon the differences observable between the sexes—in the shape, magnitude, and length, number of articulations, ramification and plumage, and individual joints of their antennæ.

With regard to their shape, variations are sometimes observable between the antennæ of the sexes; but this principally occurs in the Hymenoptera order. For instance, those of Chelostoma maxillosa, a small bee that deposits its eggs in little holes in posts and rails, are clavate in the female and filiform in the male[774]—a circumstance that distinguishes in some degree those of Sphecodes, Halictus, and Andrena of Latreille, three other genera of wild-bees[775]. In Dinetus Jur. the male antennæ are moniliform at the base, and filiform at the apex; the female, on the contrary, are entirely filiform[776].

[Pg 319]

The antennæ of the sexes also sometimes differ in magnitude and length. This is the case in the three genera of wild bees just mentioned; those of the female being thicker than those of the male, while these last are longer than the former. But in this tribe the males of the Fabrician genus Eucera are most remarkable for their long antennæ[777]. With regard to the different length of these organs in the sexes, no insects are more distinguished than some species of the capricorn-beetles (Cerambyx L.). In Lamia Sutor the male antennæ are twice the length of the female; and in another Brazilian species in my cabinet, related to L. annulata (Stenocorus F.), they are thrice their length. Some of the Anthribi F. approach the Cerambycidæ, not only in some other characters, but also in this circumstance:—thus the antennæ of A. albinus, a native of Britain, are vastly longer in the male than in the female; and in A. cinereus (Macrocephalus Oliv.)[778], which I suspect to be of the former sex, they are as long nearly as is usual in the tribe just named, called in France capricorn-beetles.

I may here observe, that sometimes in the sexes a difference is also to be found in the direction or flexure of their antennæ. Thus in Scolia F., Pepsis F. &c., in the males the antennæ are nearly straight, but in the females convolute or subspiral. The reverse of this takes place in Epipone spinipes, a kind of wasp, and its affinities; and Systropha Illig., a kind of bee: for in these the male antenna is convolute at the apex[779], and the female straight. In the various tribes of bees (Anthophila Latr.), these[Pg 320] organs in the latter are what is denominated broken, the main body of the antenna forming an angle with the first joints: but in the former this does not take place.

The antennas of the sexes do not always agree in the number of joints. In the bees, and many other Hymenoptera, the male has one more joint than the female; as is the case also in Œdemera notata (Cantharis acuta Marsh.). In Pteronus Laricis, a kind of saw-fly, the latter has only sixteen joints in its antennæ, while the former has twenty-four[780]. In Rhipicera marginata, a beetle, the beautiful antennæ of the male consist of thirty-two joints, while the female has no more than eleven! In Chelonus Jur. the male, on the contrary, has the smallest number of joints, namely sixteen; while the female has twenty-five[781].

In nothing do the sexes differ more materially than in the ramification of these organs, and their plumage. By attending to this, you may often detect the sexes in an instant; since the antennæ of the males in numerous instances are much more complex than those of the females. For what end the Creator has so distinguished them is not quite clear; but most probably this complex structure is for the purpose of receiving from the atmosphere information of the station of the female. A tendency to branching will be found in the antennæ of some males, in tribes where these organs are usually perfectly simple in both sexes. Thus, in the male of Chelostoma maxillosa,—mistaken for another species by Linné, which he names Apis florisomnis,—the intermediate joints on their inner side project into an angle[782]; and those of the same sex of the common[Pg 321] hornet, by means of a central sinus, have two obtuse teeth on each. With regard to more direct ramifications, some male antennæ terminate in a fork, or two branches. This is the case with Hylotoma furcata Latr., a saw-fly[783]; and the peacock-louse (Nirmus Pavonis Herm.)[784]. Others, again, have three lateral branches, as in Eulophus Geoffr. a little parasite, the male antennæ of which send forth a hairy external and rather long branch, from the base of the fourth, fifth, and sixth joints[785]. In Elater flabellicornis L., the eight last joints are flabellate, or elongated and flat, resembling the sticks of a fan in the male[786]; in the female they are shorter, and more properly may take their denomination from the teeth of a comb. In Lampyris Latreillii Kirby, the antennæ of the former are flabellate on both sides, while those of the latter are little more than serrate[787]. These organs are extremely beautiful in the males of the Rhipiceræ of Latreille. In R. marginata K. they consist of thirty-two joints, from thirty of which issues a branch, the first very short, but the rest gradually increasing in length as they approach the middle of the antenna; then gradually decreasing to the end, so as to represent an expanded fan[788]. But in none are they altogether so remarkable as in those moths that Linné denominates Bombyces Attaci, and some others. In these, in the males, these organs in their contour are lanceolate, and every joint is furnished with a couple of parallel equal branches on each side[789]. In the females these branches are shorter[Pg 322] on the whole, and alternately one long and one short; but in some, as Saturnia Pavonia, there is only one short branch or tooth on each joint in this sex[790]. In Bombyx regalis &c. only the first part of the antenna is so branched; and those of the female are setaceous and without branches. In B. versicolor, &c. there is only one branch from each side on every joint; those of the female being much shorter than those of the male. The latter sex of Pteronus Laricis Jur., a saw-fly, afford an example of a different structure, the antennæ on one side sending forth a branch from every joint but the two first; but on the other side, the nine or ten last joints also are without a branch. The female antenna is serrated[791]. In another of this tribe, Pterygopterus cinctus Klug, the male antenna resembles a single-toothed comb, being branched only on one side: that of the female, like the former instance, is serrated[792]. Whether the remarkable antennæ that distinguish the known individuals of the genus Phengodes (Lampyris plumosa F.) is a sexual character has not been ascertained; but it is not improbable that it may be, as in other Lampyridæ. A pair of delicate flexile and almost convolute plumose branches proceeds from the apex of each joint except the basal ones, which have something the air of cirri, and give a more than usual degree of lightness and elegance to these organs[793]. Other antennæ, especially in the Diptera order, assume an appearance of plumes—not from the branches that proceed from them, but from the fine long hairs that beset and adorn them. These are universally indications of the[Pg 323] male sex, those of the females being generally comparatively naked. If you take the common gnat, you will find that the antennæ of one individual are thickly fringed on each side, and tufted at the end with fine long hairs, while in the other only four or five placed at intervals in a whorl are to be perceived[794]. In Chironomus Meig., a kind of Tipula L., resembling a gnat, the male antennæ are beset on all sides with the finest hairs, and resemble a beautiful plume[795], while the females to the unarmed eye appear naked. Even in some Hymenoptera, the antennæ of the males are thus feathered, in a less degree: for instance, in Hylotoma Latr.[796] Whether the tufts and fringes which ornament, in a remarkable manner, the antennæ of many Cerambycidæ[797], are sexual characters, is not certainly known.

We are now to consider other sexual differences in these organs, resulting from the size or configuration of one or more individual joints. To begin with the first joint, or scapus. In many of the Hymenoptera, particularly the Anthophila Latr., this is elongated, and the remaining joints form an angle with it in the females: while in the other sex it is much shorter, and in the same line with the rest of the antennæ; and in Hylæus dilatatus (Melitta dilatata Kirby) the first joint in the male is dilated and shaped something like a patella[798]. In Malachius bipustulatus, &c. the sex just mentioned is peculiarly distinguished by a white excrescence on the first[Pg 324] four joints of the organs in question, most conspicuous in the second and fourth. The antennæ of male Cerocomæ are not very different[799]. Mr. Marsham has described a little Haltica under the name of Chrysomela nodicornis, from a peculiarity of the same sex not to be found in the other. The fourth joint is very large and obtriangular; in the female it is merely longer than the rest. In H. Brassicæ and quadripustulata the fifth joint is larger and longer than all but the first in the male, in their females it is only longer. In some moths (Herminia Latr., Crambus F.) there is also a knot in the middle of the male antennæ[800]. In Noterus, a water-beetle, the six intermediate joints are thicker than the rest, beginning from the fourth, and the last but one ends internally in a truncated tooth. The fifth and two following joints in the male antennæ of Meloe are larger than the rest, which distinguishes them, as well as a remarkable bend observable at that part[801].

Variations of the kind we are considering are also observable in the clava, or knob, in which antennæ often terminate. You have doubtless observed that the lamellated clava of the antennæ of the common cockchafer is much longer and more conspicuous in some individuals than in others—the long clava belongs to the male[802]. In another species, M. Fullo, that of this sex is nine or ten times the length of that of the other. In Colymbetes serricornis, a water-beetle, the male has a serrated clava of four joints. In Dorcatoma dresdensis[803], and also Enoplium damicorne, two beetles, it is nearly branched in the[Pg 325] male, but much less so in the female. In a little destructive beetle, common in our houses (Attagenus Pellio), in the latter it is very short, but in the former it is very long, and nearly formed by a single joint. In Eurhinus Kirby, a New Holland genus of the weevil-tribe, in the male the last joint, also, is much longer than it is in the female[804]. These examples will give you some idea of the principal variations that take place in the antennæ of the sexes, and of the wonderful diversity of forms in this respect to which mere sexuality gives rise amongst insects.

In the eyes, or stemmata, this diversity is less remarkable. Latreille has described two ants, Formica contracta and coeca, in the neuter of which he could discover no eyes[805]: in the former, the female, however, had large ones. The male he appears not to have known, but it probably was not destitute of these organs; of the latter he was acquainted only with the workers. The neuter of Myrmica rubra, another ant, has no ocelli or stemmata, although the male and female are provided with them[806]. They are discoverable only in the former sex of that singular insect related to the ants, Mutilla europæa. Other insects differ in the size of the eyes of their sexes. In the hive-bee, and some Ephemeræ, the eyes of the drone or male are much larger than those of the worker and female, and also meet at the vertex, having their stemmata below the conflux; whereas in these latter they are widely distant[807]. In Stratyomis, Tabanus, and many other[Pg 326] two-winged flies, the male eyes meet at some point below the stemmata, and above the antennæ. In the former they touch more at an angle; for the vertex forming a narrow isosceles triangle, and for the anterior part of the face one nearly equilateral: while those of the female are separated by a considerable interval. In Heptatoma and Hæmatopota in that sex, a similar interval obtains; while in the other, after forming a minute short triangle, they unite for a considerable space, and then diverging, form the face. This is also the case in Tabanus; but in the female, the space that intervenes between the posterior part of the eyes is much narrower than in these two cognate genera of the horse-flies. In some others of this order, as Musca Latr., the eyes of the male do not touch, but approach posteriorly much nearer to each other than those of the other sex. In a few instances the sexes vary even in the number of their eyes, as well as the size. This occurs in some species of Ephemera L. (E. diptera, &c.), in which the male, besides the common lateral ones, has two large and striking intermediate eyes, that sit upon vertical pillars or footstalks[808].

2. The Trunk. The thorax of many coleopterous males, especially of the Dynastidæ and Copridæ amongst the petalocerous tribes, exhibits very striking differences from that of the female. In many Lucani the lateral angle is more prominent. In Anthia it is bilobed posteriorly, while in the last-mentioned sex it is entire[809]. In Phanæus carnifex MacLeay (Copris F.) it is elevated into a plane triangular space, with the vertex of the triangle[Pg 327] pointing to the head; but in the female it is convex, with an anterior abbreviated transverse ridge[810].

In a large proportion terrific horns, often hollow, like those of the head lately noticed, arm the thorax of the male, of which you will usually only discover the rudiments in the other sex. In the first place, some are unicorns, or armed only with a single thoracic horn, which frequently, in conjunction with the thorax itself, not a little resembles a tunnel reversed: of this description are Dynastes Hercules, Tityus, Gedeon, Enema, &c.[811] In the three first this horn is porrected, or nearly in the same line with the body; but in the last, and D. Pan, it forms an angle with it; and in D. Ægeon it is nearly vertical[812]. In D. Hercules it is very long; in D. Alcides[813] and Tityus very short; in the two last, and in Oxytelus tricornis which is similarly armed, it is undivided at the apex; but in D. Gedeon, Pan, bilobus, &c.[814] it is bifid or bilobed. It is usually rather slender, but in D. Chorinæus[815] and bilobus, it is very stout and wide. In D. claviger it is hastate at the apex[816]. In D. hastatus it is short and truncated[817]. Others, again, have two thoracic horns. In Copris nemestrinus these are discoidal, diverging, and inclining forwards[818]. In Phanæus floriger[819] they are lateral, triangular, and incline towards each other, with, as it were, a deep basin between them. In P. splendidulus they sink into two longitudinal ridges, most elevated[Pg 328] posteriorly, with an intervening valley[820]. In P. bellicosus they are posterior, compressed, truncated, and emarginate at the apex, and include a basin[821]. In Copris Sabæus they are merely two acute prominences[822].—Three horns distinguish the thorax of many. In D. Aloeus[823] and its affinities, they are arranged in a triangle, whose vertex is towards the head. In D. Antæus[824] these horns are nearly equal in length, and undivided at the apex. In D. Titanus[825] the anterior horn is longer than the rest, and bifid at the apex; in D. Atlas and Endymion[826], both of which have a horn on the head, it is much shorter. In others, as in Megasoma Kirby, the vertex of the triangle is towards the anus. In M. Typhon[827] it is longer than the anterior ones, and bifid at the apex; in M. lanigerum they are equal in length[828]. In M. Elephas and Actæon[829] it is merely an elevation of the thorax; in the last almost obsolete. In Geotrupes Typhæus, common on our heaths, the anterior of this part is armed by three horizontal horns, the intermediate one being the shortest[830]. Copris lunaris also, another of our own beetles, has three short posterior thoracic horns, two lateral and triangular ones, and a transverse intermediate elevation, with a notch in the middle[831]. In Dynastes Neptunus the horns are porrected, the middle one being very long, and the lateral ones short[832]. In D. Geryon the point of the lateral[Pg 329] horns is towards the anus, and the base of the intermediate one covers the scutellum[833]. Others have four of these singular arms: this is the case with one of our rarest beetles, Bolbocerus mobilicornis K., which has four dentiform horns, the intermediate pair being the shortest, arranged in a transverse line on the anterior part of the thorax[834]. In B. quadridens these are merely teeth. In Phanæus Faunus[835] it has two lateral, elongated, compressed, truncate, horizontal horns, and two intermediate teeth. Dynastes Milon has a still greater number of horns on the thorax of the male, there being two lateral anterior ones and three posterior ones—the intermediate being the longest[836]; and Copris Antenor Fabricius and Olivier describe as having a many-toothed thorax; and from the figure of the latter[837], the male appears to have seven prominences.

But the males of insects are not only occasionally distinguished by these dorsal arms—in a few instances they are also furnished with pectoral ones. The illustrious traveller Humboldt found in South America a species of weevil (Cryptorhynchus Spiculator Humb.), the breast of which was armed with a pair of long projecting horns; and I possess both sexes of four species, three at least from Brazil, that exhibit in one individual the same character. One, concerning the country of which I am uncertain, recedes somewhat from the type of form of the rest, and comes very near that of Rynchænus Strix F.[838] In the individual which I take to be C. Spiculator, the pectoral horns are very long, curving upwards at the[Pg 330] apex, and nearly in a horizontal position; while in the three others they are much shorter, and inclined towards the horizon. The males of some species of Rynchites, as R. Bacchus and Populi[839], are also armed with a pair of lateral horns or spines, which may be termed pectoral rather than dorsal.

I shall now advert to the sexual characters that are to be found in the instruments of motion attached to the trunk—beginning with those for flight. In the female of the common glow-worm (Lampyris noctiluca) not the slightest vestige of elytra or wings is visible, and it resembles a larva rather than a perfect insect; yet its mate is a true beetle furnished with both. The same circumstance distinguishes the female cockroach (Blatta) and is more universally prevalent in that genus than in Lampyris, in which a large number of females have both elytra and wings. The males of Bombyx antiqua and Gonostigma, and of many other moths, have wings of the usual ample dimensions, while those of their females are merely rudiments. This is the case, also, with some of the Ichneumonidæ[840]. In the tribes of Ants, Termites, &c. the neuters or workers are without wings. Amongst the plant-lice (Aphides) there are individuals of both sexes, some of which have wings, and others not[841]. Amongst the Coleoptera, the female of Tenebrio Molitor, the common meal-worm, has elytra and no wings; while the male has both[842].—Sometimes these organs vary in size in the sexes: thus in Aradus Betulæ F., a kind of bug, the hemelytra and wings are narrower and shorter in the[Pg 331] female than in the male[843]. In the genus Blaps F., the mucro that arms the apex of each elytrum is longer in the former sex than in the latter. In Ateuchus gibbosus F., a dung-beetle, the elytra have a basal gibbosity near the suture in one sex that does not obtain in the other. In the Orthoptera order, the sexes are often to be known, almost at first sight, by a difference in the veining and areolets of the wings; but upon this I enlarged so fully when I treated of the sounds produced by insects, that it is not necessary to repeat what I have said; which observation also applies to the drums which distinguish the male Cicadæ[844]. The wings of some butterflies, and of most moths and hawkmoths (Sphinx L.), are furnished with a singular apparatus for keeping them steady, and the under-wing from passing over the upper in flight. This appears to have been first noticed by Moses Harris, and was afterwards more fully explained by M. Esprit Giorna[845]. From the base of the under-wing proceeds a strong bristle, received by an annulus or socket, which springing between the two principal nervures of the upper-wing terminates in the disk of the wing: in this annulus the bristle moves to and fro, and prevents the displacement of the under-wing. This apparatus is perfect only in the males, which alone have occasion for long flights; the females, though they have often several bristles, having no annulus[846].

The other instruments of motion, the legs, also differ in the sexes. In some instances they are disproportionably long. This is particularly the case with the anterior pair[Pg 332] of some beetles, as Macropus longimanus, Scarabæus longimanus L., in which they are so long as to make the males of these individuals rather inconvenient in a cabinet. Amongst British beetles Clytra longimana and Curculio longimanus Marsh. are also remarkable in this respect. In some other males the middle pair are the longest; as in Anthophora retusa Latr., a kind of wild-bee[847]. There are two known instances of remarkably long posterior legs in the Capricorn tribe, which I suspect belong to the present head. One is Saperda hirtipes Oliv.[848], in which the hind-legs are longer than the whole body, and adorned with a singular tuft of hairs; and the other a Clytus, I think, which Mr. MacLeay purchased from the late Mr. Marsham's collection, in which the hind-legs are not only very long, but have tarsi convolute, like some antennæ. From analogy I should affirm that these were the characters of male insects.

To come to the parts of legs. Sometimes the coxæ of the last mentioned sex are distinguished from those of the female by being armed by a mucro or spine. Thus the male of Megachile Willughbiella, and others of that tribe, have such a spine on the inner sides of the anterior coxa[849]. The Trochanter also of some differs sexually; and you will find that the posterior one of the male in Anthidium manicatum is of a different shape from what it is in the female[850]. In Sphodrus leucopththalmus, one of the beetles called black dors, in one sex the same trochanter[Pg 333] terminates in a long mucro or spine[851], and in the other it is rounded at the apex.

Peculiar characters in their thighs also often indicate different sexes. In Prionus damicornis there is a short spine at the apex of the anterior ones in the female that is not in the male; while in Macropus longimanus, at their base externally the male is armed with a mucro, which I cannot find in the female[852]. In Scarabæus longimanus L. this thigh is furnished with two teeth[853].—The intermediate thighs also sometimes differ. In an Onitis from China, a variety perhaps of O. Sphinx, those in the male are dolabriform, and in the other sex of the ordinary shape. In Odynerus spinipes they have on their lower side two sinuses, so as to give them the appearance of being toothed. The posterior thighs are sometimes incrassated in the male, and not in the female. This you will see in a weevil, not uncommon, Apoderus Betulæ, and also in many species of Cimbex F., a kind of saw-fly; and the same circumstance distinguishes the latter sex in many species of Lygæus F., a kind of bug: I discovered this from L. cruciger, of which I have both the sexes; and from Stoll's figure of L. Pharaonis[854]. In some of these the female thighs are enormously large. A remarkable variation in this respect is observable in the coleopterous genus Œdemera (Necydalis L.). In Œ. Podagrariæ these limbs are incrassated in one sex and not in the other[855]; in Œ. cærulea they are so in both sexes; and in Œ. ceramboides[Pg 334] in neither. In Pelecinus Polycerator F., one of the Ichneumon tribe, or an insect very near it from Brazil, these thighs in the female are armed with two spines underneath, which are not in the male.

The anterior tibiæ in Scarabæus longimanus L. differ remarkably in the sexes. In the female they are of the ordinary shape, and serrated externally; but in the male they are very long, incurved, and without teeth or serratures[856]. In the males of the genus Onitis F. they are bent like a bow, and acute at the end; but in the females they are formed on the common type[857]. In Hispa spinipes F. they are armed internally with a crooked spine[858]. But the most extraordinary sexual variation of this joint of the leg may be seen in the male of Crabro cribarius F. and several other species of the same family, in which these tibiæ are dilated externally into a concavo-convex plate, or rather have one fixed to them and part of the thigh, of an irregular and somewhat angular shape[859], with numerous transparent dots, so as not badly to resemble a sieve: whence the trivial name of the species. Rolander, who first described it, fancied that this plate was really perforated, and that by means of it the animal actually sifted the pollen; but it is most probably for sexual purposes. In another species, the plate is ornamented with transparent converging streaks. In the bee-tribes (Anthophila Latr.) the posterior tibia of the working sex is generally bigger than the corresponding part in their more idle partners: this is particularly[Pg 335] conspicuous in the genus Euglossa, in the females of which this part is triangular, very broad towards the apex, and fitted for carrying a large mass of pollen paste. The tibiæ of the males of some Lepidoptera are remarkable in this respect. That of Hepialus Humuli is much more hairy; but in H. Hectus it is a dilated mis-shapen mass, without a tarsus, and with long scales pendent from the disk[860]. Differences of this kind also occur in the calcaria or spurs that arm the apex of the tibiæ of a large number of insects. Thus in Acanthopus Klug, a singular bee, in the male the spur of the intermediate leg is dilated at the apex, and armed with six strong spines, the inner one larger than the rest[861].

But the part of the leg in which the sexes most vary is the tarsus; and this variation takes place both in the number of the joints, and their form and circumstances. The first case has been observed only with regard to certain species of Cryptophagus Herbst, as C. fumatus, &c. in which the female is pentamerous, or having five joints in all the tarsi; and the male heteromerous, or having five joints in the two anterior pairs, and only four in the posterior[862]. With respect to the form of the tarsal joints, the sexes more frequently differ; and by inspecting this part, especially in the predaceous and carnivorous Coleoptera, you may often, without further examination, ascertain whether any individual is male or female. Even in the slender-footed Cicindelidæ, the three first joints of the anterior tarsus of the male are more dilated than the two last, and covered underneath with a brush[Pg 336] of stiffish hair; in the female all are equally slender, and not so hairy. In Carabus, Feronia, &c. Latr. the four first joints of these tarsi in the males are dilated, and furnished with a brush or cushion: in the Silphidæ, also, the same circumstance takes place. In Harpalus Latr., and Silpha americana, the four anterior ones are similarly formed in this respect. But one of the most remarkable sexual characters, in this tribe of insects, that distinguish the males, are those orbicular patellæ, furnished below with suckers of various sizes, and formed by the three first joints of the tarsus, which are to be met with in the Dytiscidæ, &c.; but as I shall have occasion to treat of these more fully in another Letter, I shall only allude to them now. The second pair of tarsi have in these also the three first joints dilated and cushioned[863]. In Hydrophilus piceus, another water-beetle, the fifth joint of the tarsus is dilated externally, so as to form nearly an equilateral triangle[864]. Christian, a German writer on the Hymenoptera, has described some very singular appendages which he observed on the first joint of the four posterior tarsi of Xylocopa latipes F. These were battledore-shaped membranaceous laminæ, with a reticulated surface, of a pale colour; which were fixed in pairs by the intervention of a footstalk to the above joint, on which they sometimes amounted to more than a hundred: the use of which, he conjectures, is the collection of pollen[865]. I possess two specimens of this bee; one has none of these appendages, and on the other I can discover them only in one of the tarsi—from which circumstance I am[Pg 337] led to conjecture that, like the supposed Clavariæ that were imagined to grow on some humble-bees, but which are now ascertained to be the anthers of flowers—these also belong to the kingdom of Flora, and are spoils which the bee in question has filched from the blossom of some plant. The individuals that have been thus circumstanced are males; whether the female is guilty of similar spoliations is not known. In my specimen there are no traces of them. In many bees, the first joint of the posterior tarsi is much larger in the females and workers than in the males; but in the hive-bee this joint is largest in the latter[866]. In Beris clavipes and Empis nigra, two flies, the joint in question is large and thick in the male, but slender in the female. The penultimate tarsal joint in the posterior legs is dilated internally, and terminates in a mucro in one sex of Anoplognathus Dytiscoides of Mr. W. MacLeay[867]. In some insects the anterior tarsus of the males has been supposed to be altogether wanting: I allude to the petalocerous genus Onitis F.; but I have a specimen of Onitis Apelles of this sex, or a species nearly related to it, in which one of these tarsi is to be found[868]; which, though very slender, consists of five joints, and is armed with a double claw: from which circumstance it may, I think, be concluded, that although, as in Phanæus, these tarsi are very minute, they are not wanting. What renders this more probable is, a circumstance which every collector of insects, who has many specimens of Mr. W. MacLeay's Scarabæidæ in his cabinet, must have noticed: namely, that in all, except Copris[Pg 338] and Onthophagus, the anterior tarsi are usually broken off. Out of seventeen individuals of Scarabæus MacLeay in my own, not a single one has a relic of an anterior tarsus; and scarcely one in a much greater number of Phanæi. The tarsus in question in the nobler sex in Crabro, at least in C. cribrarius and its affinities, is also very short, especially the three intermediate joints; but at the same time very broad and flat. In the species just named, the external claw forms a kind of hook; and in the rest it is considerably longer than the other[869]. The claws, indeed, occasionally vary in the sexes in other Hymenoptera: thus in Melecta Latr., a kind of bee, in the female they are intire, but in the male they are furnished with an internal submembranaceous tooth or process[870]. In Cœlioxys conica and others, those of the latter sex are bifid at the apex, but those of the former acute[871]. In Megachile, the male claw is as in the instance just mentioned, while the female has a lateral tooth[872]; and a similar character distinguishes the sexes in the hive-bee[873].

3. The abdomen. This part affords many external sexual characters, whether we consider its general shape; the number of segments that compose it; its base, middle, or extremity.

In general shape it often differs in the sexes. Thus, the abdomen of female Tipulæ is lanceolate; that of the male cylindrical, and thickest at the extremity[874]. In[Pg 339] Molorchus F. it is convex above in the former, and flat in the latter,—the female of this beetle not unaptly representing some female Ichneumons in this respect, and the male their males[875]. In Andrena it is oblong in the one, and lanceolate in the other. In the hive-bee the drones have a thick, obtuse, and rather long abdomen; in the females it is long, and nearly represents an inverted cone; and in the workers a three-sided figure, or prism.

The number of segments, also, is generally different in the two sexes—the male having one more than the female; but in Dytiscus marginalis, &c. the reverse of this takes place: the female, if you reckon the bipartite half-concealed anal segment as one, having seven ventral segments, and the male only six. She has also eight dorsal, and the male seven.—In the ant tribes (Formica L.), the little vertical scale, at the base of the abdomen in one description of them, or the double knot in another, is less in the male than in the female. In a very singular male insect belonging to the Vespidæ, and related to Synagris, (which I purchased from the late Mr. Drury's cabinet,) the second ventral segment sends forth from its disk two remarkable parallel very acute and rather long spines. The same sex of Chelostoma maxillosa has likewise on the same segment a concave elevation, opposite to which on the fifth is a cavity which receives it, when the animal rolls itself up to take its repose[876]. In another species, C. Campanularum, the segment in question has only a tubercle[877].

On the second segment of the abdomen of some specimens,[Pg 340] probably males, of the remarkable African genus Pneumora before alluded to[878], there are thirteen little elevated ridges, placed rather obliquely in an oblique series; and gradually, though slightly, diminishing in size towards the belly: on their upper side they are flat, forming nearly a horizontal ledge, but on the lower they slope to the abdomen. The posterior thigh in its natural position covers the three first of them, and, if moved downwards, would strike them all[879]. I conjecture, therefore, that these are the animal's instruments of sound, imitating the harp or violin rather than the drum; and that the thigh acts the part of the hand or bow. The abdomen of these insects being blown out like a bladder, and almost empty[880], must emit a considerable sound when the thigh of the animal passes briskly over these ridges; and their different length would produce a modulation in the sound. When struck with a pin, they emit a grating noise.

In Staphylinus splendens, the penultimate ventral segment is very deeply cleft, and the antepenultimate emarginate in one sex, and intire in the other. In S. laminatus, an allied species, the penultimate segment is cleft, less deeply, however; but the antepenultimate is very short and intire; while the fourth is extremely long, and rounded at the margin, appearing as if it was only an elevated part of the last-mentioned segment; for which it was mistaken by Gravenhorst[881], while it is of the usual form in the other sex.

[Pg 341]

The extremity of the abdomen or its anal segments and organs furnish a variety of sexual characters. Sometimes the last dorsal segment is emarginate in the male, and not in the female; as in Megachile ligniseca, one of the leaf-cutter bees, Cimex hæmorrhoidalis, &c.[882] At other times little lateral teeth are added to this notch, as in another of the same tribe, M. Willughbiella[883]. Again, in other males, both the ventral and dorsal anal segment are armed each with a pair of teeth or mucros, as in Chelostoma maxillosa[884]. In Anthidium manicatum, another bee, the anus terminates in five spines[885]. In Cœlioxys conica of the same tribe, in which this part in the female is very acute, that of the male is armed with six points[886]. In that singular Neuropterous genus Panorpa, while the abdomen of the female is of the ordinary form, with a pair of biarticulate palpiform organs attached to the last retractile joint, or ovipositor, that of the male terminates in a jointed tail, not unlike a scorpion's, at the end of which is an incrassated joint armed with a forceps[887]. In the common earwig (Forficula auricularia) the two sexes differ considerably in their anal forceps: in one it is armed with internal teeth at the base, and suddenly dilated, above which dilatation it is bent like a bow: in the other it is smaller, without teeth, grows gradually narrower, is very minutely crenulate from the base to the end, and is straight, except at the very summit, where it curves inwards. Misled by these and similar differences, Mr. Marsham[Pg 342] has considered them (the sexes both of F. auricularia and F. minor) as distinct species.

The tail of some species of the genus Ephemera is furnished with three long, jointed, hairy bristles. We learn from Reaumur with respect to one, that though in the female these are all equal in length, yet in the male there is only a rudiment of the third. On the belly near the anus these males have four fleshy appendages, the posterior ones setaceous and long, and the anterior pair filiform and shorter. They are supposed to represent the anal forceps of other insects[888]. In Ephemera vulgata, described by De Geer, both sexes have three bristles, but those of the male are the longest; and he describes the forceps as consisting of only a pair of jointed pieces, forming a bow not unlike the forceps of an earwig[889].

v. All the differences I have hitherto noticed between the sexes of insects occur in their bodily structure; but there are others of a somewhat higher description observable in their character. You may smile at the idea of character in beings so minute; but if you recollect what I formerly related to you when treating upon the societies of insects, you will allow that something of this kind does take place amongst them. In general the males are more fitted for locomotion and more locomotive; and the females, on the contrary, are necessarily more stationary. And this for an obvious reason:—the law is, that the male shall seek the female, and therefore he is peculiarly gifted for this purpose, both in his organs of sensation and motion: while his partner in many cases has very simple antennæ, he has very complex ones; and[Pg 343] while she has either no wings or only rudiments of them, he is amply provided with them. Again: amongst the insects that suck the blood of man or beast, such as the gnat (Culex) or horse-flies (Tabanidæ), it is the female alone that is bloodthirsty, the males contenting themselves with the nectar of flowers[890]. But the difference of character in the sexes is most conspicuous, at least it has been more noticed, in those that live in societies, and is quite the reverse of what takes place in the human species. While the females and workers (which are now generally considered as sterile females, in which the ovaries are not developed) are laborious and active, diligent and skilful, wise and prudent, courageous and warlike;—the males, on the contrary, take no part in promoting the common weal, except merely a sexual one. Though till a certain period they are supported at the expense of the community, they take no part in its labours, either in collecting and forming the public stores, or in feeding and attending the young. They are idle, cowardly, and inactive; have neither art nor skill of any kind, and are unprovided with the usual offensive weapons of their species. These observations in their full force apply particularly to the hive-bee, and partially to the other social insects; amongst which, if you consult my former communications, there are some exceptions to this slothful character in the males[891].

II. Age. There is less diversity in the duration of the lives of insects in their perfect than in their larva or pupa[Pg 344] state. Some, like several species of Ephemeræ, live only a few hours; some never even see the sun[892]: others, as flies, moths, and butterflies, and indeed the majority of insects, a few days or weeks; and a comparatively small number, such as some of the larger Coleoptera, Orthoptera, &c., six, nine, twelve, or fifteen months—a period beyond which the life of perfect insects rarely extends. Some, however, certainly enjoy a longer existence in the perfect state. Mr. Baker kept one of the darkling beetles (Blaps Mortisaga) alive under a glass upwards of three years. The rose-beetle (Cetonia aurata), Rösel informs us he fed with fruit and moist white bread for as long a period[893]. Esper kept our most common water-beetle (Dytiscus marginalis) in water in a large glass vessel, feeding it with meat, for three years and a half[894]. With regard to the Arachnida, from the very slow growth of Scorpio europæus, Rösel suspects that it must live two or three years; and Audebert is stated to have kept a spider for several[895]. In this respect insects follow a law very different from that which obtains amongst vertebrate animals. In these the duration of their life is in proportion to the term of their growth: those which attain to maturity the latest, in almost every case living the longest. In insects, on the contrary, we often meet with the very reverse of this rule. Thus the larva of the great[Pg 345] goat-moth (Cossus ligniperda) is three years, that of the cabbage-butterfly (Pieris Brassicæ) not three months, in attaining maturity; yet the perfect insects live equally long. Melolontha vulgaris, which in its first state lives four years, as a beetle lives only eight or ten days[896]. And some Ephemeræ, whose larvæ have been two years in acquiring their full size, live only an hour; while the flesh-fly, whose larva has attained to maturity in three or four days, will exist several weeks.

There is yet another anomaly in the duration of the life of perfect insects. This is not, as in larger animals, a fixed period liable to be shortened only by accident or disease, and incapable of being prolonged; but an indeterminate one, whose duration is dependent on the earlier or later fulfilment of a particular animal function—that of propagation. The general law is, that a few days, or at most weeks, after the union of the sexes, both perish, the female having first deposited her eggs. If, therefore, this union takes place immediately after the disclosure of the insect from the pupa, their existence in the perfect state will not exceed a few days or weeks, or in some cases hours, as in that of the Ephemera, and likewise of the Phalænæ Attaci L. &c., which fall down dead immediately after oviposition[897]. But if by any means it be put off or prevented, their life may be protracted to three or four times that period. Gleditsch asserts, that by keeping apart the sexes of a grasshopper, their lives were prolonged to eight or nine weeks, instead of two or three, their ordinary length; and under similar circumstances Ephemeræ, which usually perish in a day, have[Pg 346] been kept alive seven or eight. It is in consequence of this very curious fact, which has not received from physiologists the attention that it merits, that many butterflies and other insects, which, when excluded from the pupa in summer, perish in less than a month, live through the winter, if excluded late in the autumn, and the union of the sexes does not ensue. It is probable that the great age to which Baker's Blaps, Rösel's Cetonia, and Esper's Dytiscus attained, was owing to their being virgins when taken, and subsequently kept from any sexual intercourse. A parallel case happens in the vegetable kingdom:—if annual plants are kept from seeding, they will become biennial; as, likewise, if they are sown too late in the year to produce seeds.

In the case, however, of the earlier or later exclusion of the imago, another agent has probably some influence. Buffon found that, other circumstances being alike, the silkworm-moths placed in a northern, lived longer than those exposed to a southern aspect: whence it appears that the stimulus of heat shortens the lives of insects, and consequently that cold tends to lengthen them.

It must be observed too, that as the death of the female insect does not take place until all the eggs are excluded, the term of her life, though usually short in the majority of species, which lay their whole number at once, is proportionably long in those which, like the queen-bee, have a longer period assigned them for this important office. Huber affirms, that he had certain proofs that she was engaged for two years in laying eggs, all impregnated by a single sexual union[898]; and in the[Pg 347] females of most insects that live in society, several months are required to mature the last eggs that are in the ovary. There is one tribe of insects, however, the females of which are affirmed to survive this operation: I mean Dorthesia Bosc; after which they even moult, though not so often as before[899].

I formerly related to you the singular fact, that the drones in a beehive at a certain period are without mercy slaughtered by the workers[900]. A fact the reverse of this is recorded by Morier with respect to the locusts: he affirms that the female, when she has done laying her eggs, is surrounded and killed by the males. He says that he never himself witnessed this extraordinary circumstance; but that he heard it from such authority that he gave full credit to it[901]. It is a fact, however, that seems to require further evidence to entitle it to such credit. These are instances in which, by a law of nature, the life of these insects is shortened by violence. It does not appear to have been ascertained how long those drones live that, under particular circumstances, as stated in a former letter[902], are exempted from the usual slaughter.

I am, &c.

[Pg 348]

LETTER XXXIII.

EXTERNAL ANATOMY OF INSECTS.

TERMS, AND THEIR DEFINITION.

Having shown you our little animals in every state, and traced their progress from the egg to the perfect insect, I must next give you some account of their structure and anatomy. And under this head I shall introduce you to a microcosm of wonders, in which the hand of an Almighty workman is singularly conspicuous. One would at first think that the giant bulk of the elephant, rhinoceros, or hippopotamus, must include a machine far more complicated, a skeleton more multifarious in its composition—covered by muscles infinitely more numerous—instinct with a nervous system infinitely more ramified—with a greater variety of organs and vascular systems in play, than an animal that would scarcely counterpoise a ten-millionth portion of it. Yet the reverse of this is the fact; for the Creator, the more to illustrate his wisdom, power, and skill, has decreed that the minute animals whose history we are recording, shall be much more complex in all the above respects than these mighty monarchs of the forest and the flood. Of this in the present and subsequent letters you will find repeated[Pg 349] and scarcely credible instances, which in every rightly constituted mind are calculated to excite, in an extraordinary degree, those sensations of reverence and love for the Invisible Author of these wonders, and that faith and trust in his Power and Providence, which an attentive survey of the works of Creation has a natural tendency to produce. And you will not only be struck by this circumstance, but equally by the infinite variations in the structure that will present themselves to your notice; and that not sudden and per saltus, but by approaches made in the most gradual manner from one form to another. And all along, where the uses of any particular organ or part have been ascertained, if you consider its structure with due attention, you will find in it the nicest adaptation of means to an end: a circumstance this, which proves most triumphantly, that the Power who immediately gave being to all the animal forms, was neither a blind unconscious power, resulting from a certain order of things, as some philosophists love to speak[903]; nor a formative appetency in the animals themselves, produced by their wants, habits, and local circumstances, and giving birth, in the lapse of ages, to all the animal forms that now people our globe[904]; but a Power altogether distinct from and above nature, and its Almighty Author[905].

[Pg 350]

I trust that what I have here advanced will excite your attention to the subject I am now to enter upon; and I flatter myself, that although at first sight it may promise nothing more than a dry and tedious detail of parts and organs, you will find it not without its peculiar interest and attraction.

This department of the science—the Anatomy of Insects—may still be regarded as in its infancy; and considering[Pg 351] the almost insuperable difficulties which, from the minuteness of the objects, oppose themselves to the skill and instruments of the entomological anatomist, we can scarcely hope that it will ever attain to that certainty and perfection to which, as far as the larger animals are concerned, anatomy has arrived. Yet infinitely more has been accomplished than might have been expected, and new accessions of light are daily thrown upon it. When[Pg 352] we consider what has been done by Malpighi, Leeuwenhoeck, and especially Swammerdam, we admire the patience, assiduity, and love of science, that enabled them, in spite of what seemed insurmountable obstacles, to ascertain, the first with respect to the silk-worm, and the latter in numerous instances, the internal organization of these minute creatures, as well as their external structure. Reaumur, and his disciple De Geer, extending their researches, have also contributed copiously to our knowledge in this branch of our science.

But in this field no one has laboured so indefatigably and with so much success as the celebrated Lyonnet; and though his attention was confined to one object—the caterpillar of the goat-moth (Cossus ligniperda F.),—every one who studies his immortal work must admire the patient and skilful hand, the lyncean eye, and keen intellect, that discovered, denuded, and traced every organ, muscle, and fibre of that animal. Much is it to be regretted that his proposed works on the pupa and imago of the same insect, which, he informs us, were far advanced[906], were never finished and given to the world. Our regret, however, is in some degree diminished by the elaborate work of M. Herold on the butterfly of the cabbage (Pieris Brassicæ), before eulogized[907]; in which he has done much to supply this desideratum.

In more modern times, besides Herold, MM. Latreille, Illiger, Marcelle de Serres, Savigny, Ramdohr, Treviranus[Pg 353] Sprengel, Audoin, Chabrier, and, above all, M. Cuvier in his celebrated Lectures on Comparative Anatomy, have considerably extended the boundaries of our knowledge in this department: and much of what I have to say to you in my letters on this subject, will be derived from these respectable sources. In the exterior anatomy of insects, I flatter myself that I shall be enabled to make some material additions to the discoveries of my predecessors; though few have occurred to me with respect to their internal organization.

In treating of the anatomy of the vertebrate animals, it is usual, I believe, to consider, first, the skeleton and its integuments, whether of skin or muscle, and their accessories; and afterwards the organs of the different vital functions and of the senses. But in considering the anatomy of Insects, the difference before stated[908], observable between them and the sub-kingdom just mentioned, as to their structure, renders it advisable to divide this subject into two parts—the first treating of their external anatomy, and the second of their internal.—I shall begin by drawing up for you a Table of the Nomenclature of the parts of their external crust; its appendages and processes[909], external or internal, accompanied by definitions of them; and followed by such observations respecting them as the subject may seem to require for its more full elucidation.

Anatomists have divided the human skeleton into three[Pg 354] greater sections—the Head, the Trunk, and the Limbs. That of insects, likewise, is resolvable into three primary sections, but without including the limbs (which, as being appendages, and therefore secondary, had best be considered under the section of which they form a part), for the abdomen in insects, as well as the rest of the body, being covered with a crust, and forming a distinct part, may be properly regarded as a primary section. And in fact these three parts may be received as primary under another view—the head, as containing the principal organs of sensation; the trunk, as containing those of motion; and the abdomen, as containing those of generation[910]. Under each of these primary sections, I shall consider its respective organs, members, and parts.

You are not to expect to find every part included in the following Table in every insect; since it has been my aim to introduce into it, the most remarkable of those that are peculiar to particular tribes, genera, &c. With respect to these, I shall generally refer you to the individuals in which they may be found.

DEFINITIONS.

Corpus (the Body). The whole crust of the insect; consisting of the Exoderma or external covering, and the Esoderma or internal cuticle that lines it[911]. It is divided into three primary parts, or sections—Caput, Truncus, Abdomen.

INSERT FOLDOUT HERE

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[Pg 355]

I. CAPUT (The Head).

The Head is the anterior section of the body; consisting of a kind of box without suture or segment, which receives the organs of sensation and manducation. It includes the Os, Facies, Subfacies, and Collum.

i. Os (the Mouth). That part of the head which receives and prepares the food for passing into the stomach. It includes the Trophi[912].

1. Trophi (the Trophi). The different instruments or organs contained in the mouth, or closing it, and employed in manducation or deglutition. They include the Labrum, Labium, Mandibulæ, Maxillæ, Lingua, and Pharynx.

A Labrum (the Upper-lip). A usually moveable organ; which, terminating the face anteriorly, covers the mouth from above, and is situate between the Mandibulæ[913]. It includes the Appendicula.

a Appendicula (the Appendicle). A small piece sometimes appended to the upper-lip[914]. Ex. Halictus ♀ Walck. (Melitta **. b. K.)

B Labium (the Under-lip). A moveable organ, often biarticulate, which terminating the surface anteriorly, covers the mouth from beneath, and is situate between the Maxillæ[915]. It includes the Mentum, and Palpi Labiales.

a Mentum (the Chin). The lower joint of the Labium,[Pg 356] where it is jointed; in other cases its base. It is usually seated between the base of the Maxillæ[916].

b Palpi Labiales (the Labial Feelers). Two jointed sensiferous organs, the use of which is not clearly ascertained, which emerge, one on each side, from the Labium, mostly near its summit[917].

C Mandibulæ (the Upper-jaws). Two transverse lateral organs, in most insects used for manducation; generally corneous, moving horizontally, and closing the mouth above, under the Labium[918]. They include the Prostheca, Dentes, and Mola.

a Prostheca (the Prostheca). A subcartilaginous process attached to the inner side, near the base, of the Mandibulæ of some Staphylinidæ[919]. Ex. Ocypus similis K., Creophilus maxillosus K., &c.

b Dentes (the Teeth). The terminating points of the Mandibulæ. They include the Incisores, Laniarii, and Molares[920].

A Incisores (the Cutting-teeth). Teeth somewhat wedge-shaped, externally convex and internally[Pg 357] concave[921]. Ex. Gryllotalpa Latr., Gryllus Latr. (Acheta F.), &c. &c.

B Laniarii (the Canine-teeth). Very sharp and usually long conical teeth[922]. Ex. Forficula L., Mantis L., Libellula L.

C Molares (the Grinding-teeth). Teeth that terminate in a broad uneven surface, fit for grinding the food[923]. Ex. the herbivorous Orthoptera.

c Mola (the Mola). A broad, flat, subrotund space, transversely grooved or furrowed, observable on the inner side of some mandibles that have no grinding-teeth at their apex[924]. Ex. Euchlora MacLeay, Anoplognathus Leach, Larva of Lucanus[925].

D Maxillæ (the Under-jaws). Two organs moving subhorizontally, fixed on each side at the base of the Labium, and often parallel with it—which in masticating insects seem primarily designed to hold the food[926]. They include the Cardo, Stipes, Lobi, and Palpi maxillares.

a Cardo (the Hinge). A small, transverse, usually triangular, corneous piece, upon which the Maxilla commonly sits[927].

b Stipes (the Stalk). The corneous base of the Maxilla, below the Palpus[928].

c Lobi (the Lobes). The parts of the Maxilla above the Palpus[929]. They include the Lobus superior, the Lobus inferior, and the Ungues.

[Pg 358]

A Lobus Superior (the Upper-lobe). The outer lobe of the Maxilla, incumbent on the inner one. In the Predaceous Beetles this lobe is biarticulate and palpiform[930]; and in Staphylinus olens, &c. it also consists of two joints[931]. It is called the Galea by Fabricius, in Orthoptera, &c.[932]

B Lobus Inferior (the Lower-lobe). The inner lobe of the Maxilla, covered by the outer one[933].

C Ungues (the Claws). One or more corneous sharp claws which arm the lobes of the Maxilla[934]. In the Predaceous Beetles there is only one terminating the lower lobe, with which, in Cicindela, it articulates; in the Orthoptera and Libellulina there are several.

d Palpi Maxillares (the Maxillary Feelers). Two jointed sensiferous organs, the use of which is not clearly ascertained, emerging from an exterior lateral sinus of the Maxilla[935].

E Lingua (the Tongue). The organ situated within the Labium or emerging from it, by which insects in many cases collect their food and pass it down to the Pharynx, situated at its roots above. It varies considerably in different orders and tribes. In the Orthoptera, Libellulina, &c. it is linguiform, and quite distinct from the Labium[936]; it appears also distinct in the lamellicorn beetles, &c.[937] In many[Pg 359] Hymenoptera it emerges from the Labium, and is fitted to collect liquids and pass them downwards[938]. In Formica it appears to be retractile[939]. In a considerable proportion of insects it seems connate with the Labium, and forming its inner surface? According to circumstances it might perhaps be denominated Lingua or Ligula. It includes the Paraglossæ.

a Paraglossæ (the Paraglossæ). Lateral and often membranous processes observable on each side of the tongue in some Hymenoptera, &c.[940]

F Pharynx (the Pharynx). The opening into the gullet[941]. It includes the Epipharynx and Hypopharynx.

a Epipharynx (the Epipharynx). A small valve under the Labrum, that in many Hymenoptera closes the Pharynx, and is an appendage of its upper margin[942].

b Hypopharynx (the Hypopharynx). An appendage[Pg 360] of the lower margin of the Pharynx, observable in Eucera F.[943]