The Project Gutenberg eBook of The Sea-beach at Ebb-tide, by Augusta Foote Arnold.

This volume is designed to be an aid to the amateur collector and student of the organisms, both animal and vegetable, which are found upon North American beaches. In it are described many invertebrates and some of the more notable varieties of seaweeds, and each individual is given its proper place in the latest classification.

The technicality of classification or scientific grouping may at first seem repellent, but it in reality makes the study of these objects more simple; and a systematic arrangement has been adopted in the belief that it is the easiest as well as the only satisfactory way of becoming familiar with the organisms described. Without it a very confused picture of separate individuals would be presented to the mind, and a book like the present one would become a mere collection of isolated scraps of information. Morphology, or the study of structure, has been touched upon just enough to show the objects from the biologist's point of view and to enable the observer to go a little beyond the bare learning of names.

Scientific names have been used from necessity, for the plants and animals of the beach are so infrequently observed, except by scientific people, that but few of them have common names; and, as a matter of fact, the reader will find that a scientific name is as easily remembered as a common one. Technical phraseology has, however, been avoided as much as possible, even at the expense of conciseness and precision; where it has been used, care has been taken to explain the terms so that their meaning will be plain to every one. A general glossary has been omitted, but the technical terms used have been indexed. The illustrations will bear the use of a hand-glass, and this will often bring out details which cannot well be seen by the unaided eye.

The systematic table of the marine algæ, as given in Part I, and followed in the text, will be of use to collectors who wish to make herbaria. In order to name and group specimens such a guide is necessary. Should specific names lead to embarrassment, many of them can be neglected, for the names of genera are often a sufficient distinction.

Since so many species of invertebrates are found on the beach that a complete enumeration of them is impracticable, only the most conspicuous ones have been selected for description in Part II; but the attempt has been made to designate the various classes and orders with sufficient clearness to enable the collector to identify the objects commonly found on the shore, and to follow the subject further, if he so desires, in technical books.

It is hoped that this book will suggest a new interest and pleasure to many, that it will encourage the pastime of collecting and classifying, and that it will serve as a practical guide to a better acquaintance with this branch of natural history, without necessitating serious study. Marine organisms are interesting acquaintances when once introduced, and the real purpose of the author is to present, to the latent naturalist, friends whom he will enjoy.

Grateful acknowledgment is here made to the following persons who have kindly assisted and advised the author and have also extended valued courtesies to her in the preparation of this book: Smith Ely Jelliffe, M.D., Ph.D.; Herbert M. Richards, A.B., Ph.D., Professor of Botany in Barnard College; Marshall A. Howe, A.B., Ph.D.; the Rev. George A. Holst; the Long Island Historical Society of Brooklyn for the use of its fine herbarium, containing the collections of Mr. John Hooper, Mr. A. R. Young, and others, from which most of the illustrations of algæ in this book were photographed; Miss Toedtleberg, Librarian of the Long Island Historical Society; Miss Ingalls, in charge of the Museum of the Long Island Historical Society; Dr. Theodore Gill; James A. Benedict, Ph.D., Assistant Curator of Marine Invertebrates in the Smithsonian Institution; Miss Mary J. Rathbun, second Assistant Curator of Marine Invertebrates in the Smithsonian Institution; Miss Harriet Richardson; and especially to Mr. John B. Henderson, Jr.

Thanks, also, are due to Messrs. Macmillan & Co. for permission to use cuts from the "Cambridge Natural History," Parker and Haswell's "Zoölogy", and Murray's "Introduction to the Study of Seaweeds"; to Swan Sonnenschein & Co. for the use of cuts from Sedgwick's "Student's Text-book of Zoölogy"; to Wilhelm Engelmann for a cut from "Die natürlichen Pflanzenfamilien" of Engler and Prantl; to Little, Brown & Co. for permission to reproduce illustrations from Agassiz's "Contributions to the Natural History of the United States"; to Henry Holt & Co. for a cut from McMurrich's "Invertebrate Morphology"; to Houghton, Mifflin & Co. for cuts from the "Riverside Natural History" and Agassiz's "Seaside Studies in Natural History"; to the Commonwealth of Massachusetts for the use of illustrations from Verrill's "Report upon the Invertebrate Animals of Vineyard Sound and the Adjacent Waters," Gould's "Invertebrata of Massachusetts" (ed. Binney), and certain fisheries reports; and to the United States government for illustrations taken from Bulletin 37 of the Smithsonian Institution and from reports of the United States Fish Commission.

INTRODUCTION

The sea-shore, with its stretches of sandy beach and rocks, seems, at first sight, nothing but a barren and uninteresting waste, merely the natural barrier of the ocean. But to the observant eye these apparently desolate reaches are not only teeming with life; they are also replete with suggestions of the past. They are the pages of a history full of fascination for one who has learned to read it.

In this history even the grains of sand have a part. Though so humble now, they once formed the rocky barriers of the shore. They stood as do the rocks of to-day, defiant and seemingly everlasting, but the fury of the sea, which knows no invincible adversary, has laid them low. Every coast-line shows the destructive effects of the sea, for the bays and coves, the caves at the bases of the cliffs, the buttresses, stocks, needles, and skerries, are the work of the waves. And this work is constantly going on.

The story of the sands is not only one of the conflict of the sea and rocks; it is also a story of the winds. It is the winds that have rescued them from the waves and driven them about, sifting and assorting them, arranging them in graceful forms, and often heaping them up into dunes which, until fastened by vegetation, are themselves ever moved onward by the same force, sometimes burying fertile lands, trees, and even houses in their march. The sands, moreover, are in turn themselves destructive agents, to whose power the many fragments which strew the beach and dunes bear ample witness. The knotty sticks so commonly seen on the beach are often the hearts of oak- or cedar-trees from which the tiny crystals of sand have slowly cut away their less solid outer growth. Everything, in fact, upon the sands is "beach-worn," even to the window-glass of life-saving stations, which is frequently so ground that it loses its transparency in a single storm.

The beach is also a vast sarcophagus holding myriads of the dead. "If ghosts be ever laid, here lie ghosts of creatures innumerable, vexing the mind in the attempt to conceive them." And there are certain sands which may be said to sing their requiem, the so-called musical sands, like the "Singing Beach" at Manchester-by-the-Sea, which emit sounds when struck or otherwise disturbed. On some beaches these sounds resemble rumbling, on others hooting; sometimes they are bell-like and even rhythmical. The cause of this sonorous character is not definitely known, but it is possibly due to films of compressed gases which separate each grain as with a cushion, and the breaking of which [pg003] causes, in the aggregate, considerable vibrations. Such sands are not uncommon, having been recorded in many places, and they exist probably in many others where they have escaped observation. They may be looked for above the water-line, where the sand is dry and clean.

We have to do, however, in this volume, not with the history of the past, nor with the action of physical forces, but with the life of the present, and to find this, in its abundance, one must go down near the margin of the water, where the sands are wet. There is no solitude here; the place is teeming with living things. As each wave retreats, little bubbles of air are plentiful in its wake. Underneath the sand, where each bubble rose, lives some creature, usually a mollusk, perhaps the razor-shell Solen ensis. By the jet of water which spurts out of the sand, the common clam Mya arenaria reveals the secret of its abiding-place. A curious groove or furrow here and there leads to a spot where Polynices heros has gone below; and the many shells scattered about, pierced with circular holes, tell how Polynices and Nassa made their breakfast and their dinner. Only the lifting of a shovelful of sand at the water's edge is needed to disclose the populous community of mollusks, worms, and crustaceans living at our feet, just out of sight.

Even the tracks and traces of these little beings are full of information. What may be read in the track of a bird on the sand is thus described by a noted ornithologist:

Following the key further, he draws more conclusions. The tracks are not in pairs, so the bird does not belong to the perchers; therefore it must be a wader or a swimmer. There are no web-marks to indicate the latter; hence it is a three-toed walking or wading bird. It had flat, long, narrow, and pointed wings because it came gliding swiftly and low, and scraped the sand before its wings were closed. This is shown by the few scratches before the prints became perfect. A certain class of birds thus arrests the impetus of flight. It had a long feeling-bill, as shown by the little holes in the sands where the marks became entangled; and so on. These combined characteristics belong to one class of birds and to no other; so he knows as definitely as [pg005] though he had seen the bird that a sandpiper alighted here for a brief period, for here is his signature.

It is plain that tracks in the sand mean as much to the naturalist as do tracks in the snow to the hunter, and trails on the land to the Indian who follows his course by signs not seen by an untrained eye.

The tide effaces much that is written by foot and wing, but sometimes such signs are preserved and become veritable "footprints on the sands of time." In the Museum of Natural History in New York is a fossil slab, taken from the Triassic sandstone, showing the footprints of a dinosaurian reptile now extinct, which, in that long ago, walked across a beach—an event unimportant enough in itself, but more marvelous than any tale of imagination when recorded for future ages. From such tracks, together with fragments of skeletons, the dinosaur has been made to live again, and its form and structure have been as clearly defined as those of the little sandpiper of Dr. Coues. [pg006]

II
COLLECTING

It has been said that everything on the land has its counterpart in the sea. But all land animals are separate and independent individuals, while many of those of the sea are united into organic associations comprising millions of individuals inseparably connected and many of them interdependent, such as corals, hydroids, etc. These curious communities can be compared only to the vegetation of the land, which many of them resemble in outer form. Other stationary animals, such as oysters and barnacles, which also depend upon floating organisms for their food, have no parallel on the land.

The water is crowded with creatures which prey upon one another, and all are interestingly adapted to their mode of life. Shore species are exceedingly abundant, and the struggle for life is there carried on with unceasing strife. In the endeavor to escape pursuers while they themselves pursue, these animals have various devices of armature and weapons of defense; they have keen vision, rapid motion, and are full of arts and wiles. One of the first resources for safety in this conflict is that of concealment. This is effected not only by actual hiding, but very generally by mimicry in simulating the color of their surroundings, and often by assuming other forms. Thus, for instance, the sea-anemone when expanded looks like a flower and is full of color, but when it contracts becomes so inconspicuous as to be with difficulty distinguished from the rock to which it is attached. Anemones also have stinging threads (nematophores), which they dart out for further defense. [pg007]

The study of biology has great fascination, and the subject seldom fails to awaken interest as soon as the habit of observation is formed. Jellyfishes, hardly more dense than the water and almost as limpid, swimming about with graceful motion, often illuminating the water at night with their phosphorescence, showing sensitiveness, volition, and order in their lives, cannot fail to excite wonder in even the most careless observer. Not less interesting are the thousands of other animals which crowd the shores, lying just beneath the surface of the sand, filling crevices in the rocks, hiding under every projection, or boldly—perhaps timidly, who shall say?—lying in full view, yet so inconspicuous that they are easily passed by unnoticed.

To find these creatures, to study their habits and organization, to consider the wonderful order of nature, leads through delightful paths into the realms of science. But even without scientific study the simple observation of the curious objects which lie at one's feet as one walks along the beach is a delightful pastime.

The features which separate the classes and the orders of both the plant and the animal life are so distinctive that it requires but very superficial observation to know them. It is easy to discriminate between mollusks, echinoderms, and polyps, and to recognize the relationship between univalves and bivalves, sea-urchins and starfishes, sea-anemones and corals. The equally plain distinctions between the branched, unbranched, tubular, and plate-like green algæ make them as easy to separate.

The pleasure of a walk through field or forest is enhanced by knowing something of the trees and flowers, and in the same way a visit to the sea-shore becomes doubly interesting when one has some knowledge, even though it be a very superficial one, of the organisms which inhabit the shore.

ROCKY SHORES

Rocky shores furnish an abundance and great variety of objects to the collector. The seaweeds here find places of attachment, and the lee and crevices of the rocks afford shelter to many animals which could not live in more open and exposed places. The [pg008] rock pools harbor species whose habitat is below low-water mark and which could not otherwise bear the alternation of the tides.

The first objects on the rocky beach to attract attention are the barnacles and rockweeds. They are conspicuous in their profusion, the former incrusting the rocks with their white shells, and the latter forming large beds of vegetation; yet both are likely to be passed by with indifference because of their plentifulness. They are, however, not only interesting in themselves, but associated with them are many organisms which are easily overlooked. The littoral zone is so crowded with life that there is a constant struggle for existence,—even for standing-room, it may be said,—and no class of animals has undisputed possession of any place. Therefore the collector should carefully search any object he gathers for other organisms which may be upon it, under it, or even in it, such as parasites, commensals, and the organisms which hide under it or attach themselves to it for support. Let the rockweed (Fucus) be carefully examined. Among the things likely to be found attached to its fronds are periwinkles (Littorina litorea), which simulate the plant in color, some shells being striped for closer mimicry. Sertularian hydroids also are there, zigzagging over the fronds or forming tufts of delicate horny branches upon them. Small jelly-like masses at the broad divisions of the fronds may be compound ascidians. Calcareous spots here and there may be polyzoans of exquisite form, while spread in incrusting sheets over considerable spaces are other species of Polyzoa. Tiny flat shelly spirals are the worm-cases of Spirorbis. A pocket-lens is essential to enable one to appreciate the beauty of these minute forms. Under the rockweeds are many kinds of crustaceans; perhaps there will also be patches of the pink urn-like egg-capsules of Purpura at the base of the fucus.

Various kinds of seaweed abound in the more sheltered parts of the rocks, and among them will be found amphipods and isopods, many of which are of species different from those of the sandy beaches. Here, too, is the little Caprella, imitating the seaweed in form, and swaying its lengthened body, which is attached to the plant only by its hind legs. On the seaweeds, as well as in the tide-pool, may be found beautiful hydroids, and on [pg009] them the curious little sea-spiders (Pycnogonidæ), animals which seem to be all legs.

Mollusks, and other classes as well, differ in different latitudes. On the rocks of the Northern shores Littorina and Purpura shells are very abundant, the latter in various colors and beautifully striped. Limpets are also plentiful, but are not as conspicuous, since they have flat, disk-shaped shells. When their capture is attempted, they must be taken unawares and pushed quickly aside, else they take such a firm hold of the rock that it is difficult to dislodge them. Near low-water mark under ledges will perhaps be found chitons, which are easily recognized by their oval, jointed shells. On the California coast in like localities will be found the beautiful Haliotis, Acmæa, and chitons. Every stone that is lifted will disclose numbers of little amphipods (Gammarus), which will scuttle away on their sides to other shelter; worms will suddenly disappear into the mud, and perhaps a crab, here and there, having no alternative, will make a stand and fight for his liberty. Flat against the stone and not easily perceived may be a chiton, a planarian worm, or a nudibranch. And just below the water's edge are sea-urchins and starfishes, which grow in numbers as the eye becomes accustomed to the search.

The rock pools are natural aquaria, more interesting by far than any prepared by man. The possibilities of these little sea-gardens are beyond enumeration. The longer one studies them the more one finds. In them all classes of seaweeds and marine invertebrates may be found and their habits watched. The great beauty of these pools gives them an esthetic charm apart from the scientific interest they excite. Perhaps one may find here a sponge, and removing it to a shallow vessel of sea-water can watch the currents of water it creates. Several sponges of the same species placed in contact will at the end of two days be closely united. If the sponges are of different species they will not coalesce.

In the clefts and crannies of the rocks are various fine seaweeds, often of the red varieties, sea-anemones, hydroids, polyzoans, crustaceans, mollusks, and ascidians. Crabs will be snugly [pg010] ensconced under projecting surfaces. Most species are more plentiful at the lowest-water mark, and many are found only at this point and below.

SANDY SHORES

On sandy shores the greater part of the inhabitants live under the surface. Many give evidence of their presence by the open mouths of their burrows, and some distinctly point out these places by piles of sand or mud in coils at the opening. Some tubicolous worms have their tubes projecting above the surface. The tubes of Diopatra are hung with bits of shells, seaweeds, and other foreign matter. Some mollusks announce themselves by spurting jets of water or sending bubbles of air from the sand. The majority of the underground species, however, give no sign of their presence on the surface, and must be found by digging. Many of them go deep into the sand, and in searching for worms the digger must be quick- and expert, or he will lose entirely or cut in two many of the most beautiful ones, which retreat quickly and to the extremity of their holes at the least alarm. One can be a rambler on the sandy beach for a long time without being aware of the many beautiful objects which inhabit the subsurface of the sand. The curious crab Hippa will disappear so quickly into the sand that one is hardly sure he has really seen it. The vast number of worms will surprise any one who searches for them by their variety, their beautiful color, and their interesting shapes. Here again a glass is requisite to appreciate the delicacy and beauty of their locomotive organs, their branchiæ, and so on. The most common of the gasteropod mollusks on sandy shores are Nassa obsoleta, Nassa trivittata, and Polynices (Lunatia) heros. The last are detected by the little mounds of sand which they push before them as they plow their way just below the surface. On more southern beaches, Fulgur, Strombus, and Pyrula are the common varieties. Olivella, Oliva, and Donax, also inhabitants of sandy beaches, will quickly disappear when uncovered by the waves, being rapid burrowers. Most of the many dead shells on the beach will be found to be pierced with a round hole, which is [pg011] drilled by the file-like tongue, or lingual ribbon, of Polynices, Urosalpinx, or Nassa, which thus reach the animal within and suck out its substance. Another similar species is Polynices (Neverita) duplicata, which extends to the Gulf of Mexico, while P. heros is not commonly found below Hatteras. Crustaceans are abundant on the sandy beach over its whole breadth. Some of the sand-crabs live above tide-mark. Among these is the fleet-footed Ocypoda, which is interesting to watch. Often they go in numbers to the water's edge and throw up mounds, behind which they crouch like cats, watching for whatever prey the tide may bring up. When unable to outrun a pursuer they rush into the surf and remain there until the danger is past. The wet sand is often thickly perforated with the burrows of the sandhoppers (Orchestia). These often rise about the feet as do grasshoppers in the fields.

PLATE I.
Egg-capsules of Purpura lapillus.	Egg-case of Polynices heros.
Egg-capsules of Buccinum undatum.	Egg-case of the skate.
Fulgur canaliculata (whelk) and egg-cases.

Hippa talpoida is a remarkable crab, somewhat resembling an egg. It is not likely to be seen unless searched for by digging at the water's edge. It burrows so rapidly that one must be quick to catch it after it is exposed by the shovel. In some places the tests of "sand-dollars" are common. The living animal may be found buried just below the surface at extreme low-water mark.

The sea-wrack drifted in lines along the shore will repay careful examination, for here will be found many things belonging to other shores and deep water. It is often alive with sandhoppers, which hop away while one searches for less common things. Often the most delicate seaweeds, numerous small shells, worms, polyzoans, etc., will be found there.

The surface of the sand-beach is strewn with remains of many species, usually beach-worn, but interesting nevertheless as examples of species one would like to find in better condition, but good specimens of which elude ordinary search or are unobtainable except by dredging.

Egg-cases form another class of objects which are often gathered with no idea of their identity. Of these the most common are the long strings of saucer-like capsules which contain the eggs of the mollusk Fulgur, those having square edges being [pg012] the egg-cases of F. carica, and those having sharp edges those of F. canaliculata. Collar-like sandy rings contain the eggs of Polynices (Lunatia), which are cemented together in this shape. The boys of Cape Cod call them "tommy-cod houses." Cylindrical piles of little capsules, sometimes called "ears of corn," hold the eggs of Chrysodomus. The irregular masses of small hemispherical capsules are those of the common whelk (Buccinum). The so-called "Devil's pocket-books" are the egg-cases of the skate.

MUDDY SHORES

On muddy shores the eel-grass (Zostera marina) grows abundantly, giving an appearance of submerged meadows. It is one of the very few flowering plants which live in salt water. In summer its little green blossoms may be seen in grooves on the leaf-like blades. Many animals live on and among eel-grass. Found upon it is the delicate gasteropod mollusk Lacuna vincta, and its eggs in little rings; the iridescent Margarita helicina, and Nassa, with its bright-yellow eggs in small gelatinous masses; also little worms (Spirorbis) in tiny flat spiral shells, compound ascidians in jelly-like masses, clusters of shelly or horny polyzoans, isopods, planarian worms, and so on. Scallops (Pecten) will be found at the base of the plants, and the common prawns are very numerous, swimming freely about. Mud flats and shores are the homes of many mollusks, especially of Nassa obsoleta,—which is the most abundant shell of any considerable size from Cape Cod to the Gulf of Mexico,—and of vast numbers of the tiny Littorinella minuta, which serve as food for fishes and aquatic birds. Clams and worms of all varieties are also abundant.

There are many varieties of mud-crabs, of which the most common are the "fiddlers," which honeycomb the banks and the surface of salt-marshes with their burrows. The common edible crab Callinectes hastatus is plentiful in bays and estuaries. The sluggish spider-crabs hide beneath the surface of the mud and in decaying weeds and eel-grass. Hermit-crabs are plentiful here as well as elsewhere. Panopeus is a sluggish crab found in shallow water and in all sorts of hiding-places along the shore. It [pg013] may often be found in dead shells, and, in the South, in holes in the banks. This genus is represented by a number of species, some of which are quite pretty.

WHARVES AND BRIDGES

On the piles of wharves and bridges may often be found beautiful tubularian hydroids in large tufts just below low-water mark, branched hydroids looking like little shrubs, polyzoans, sea-anemones, mollusks, and ascidians. The species peculiar to these localities are the boring mollusk Teredo navalis, or ship-worm, the boring isopod Limnoria lignorum, and the boring amphipod Chelura terebrans, all of which penetrate the wood and are most destructive.

The animals and plants of tropical beaches and coral reefs are so various and abundant, so curious and beautiful, as to make a description or even an enumeration of them in a brief space difficult. The collector is bewildered and excited when he first views the profusion of the wonderful forms there found.

It is not generally known that a fine species of "stony coral" is common from Cape Cod southward, growing in clear water as an incrustation on rocks, and developing little spires as it advances in age. This species, the Astrangia danaë, is especially interesting, since it will live in a dish of clear sea-water, and the polyps will expand, showing a very close relationship to the sea-anemone. With care in changing the water this coral will live for days, and may be examined in its expanded condition with a lens of moderate power.

The most favorable time for collecting on any beach is at the lowest tide, many objects being then uncovered which do not appear higher up on the beach. At the spring-tides, which occur twice a month, at the period of the new and that of the full moon, the ebb is especially low, and affords an opportunity to search for forms whose habitat is below ordinary low-water mark. During storms deep-water forms are often torn from their beds and cast upon the beach. Shore-collecting at these times is often very interesting. [pg014]

EQUIPMENT FOR COLLECTING INVERTEBRATES

The equipment for collecting upon sandy beaches is a shovel, a sieve, and a net. Numerous trials should be made with the shovel from about half-tide mark to as deep as one cares to wade, and the sand raised should be carefully searched for shells, crustaceans, and worms. By washing out the sand in the sieve the smallest specimens, which might otherwise escape notice, may be secured. On a rocky beach a strong knife and a net are sufficient. It is well to have a number of homeopathic vials for small specimens, which will be injured by contact with larger forms, and jars for holding the general collection.

PRESERVING INVERTEBRATES

To preserve specimens, they should first be placed in a weak solution of alcohol, the strength of which should be increased gradually until the animal is entirely free from water and is hardened throughout. If the alcohol becomes colored and sediment falls to the bottom of the jar, the animal is degenerating, and the alcohol should be changed. Specimens for transportation can be packed by wrapping each one in a bit of cheese-cloth and then placing them together in a large receptacle. Care should be taken to keep the fragile specimens separate. Sand-dollars possess a pigment which discolors and soon vitiates alcohol, and consequently these should be separated from the other forms and placed where the alcohol may be changed from time to time as appears necessary. The homeopathic vials containing small specimens may be put into the can without injury to the other specimens. Special cans of various sizes, with handles and screw covers, are made for naturalists. One of these cans is a convenient receptacle for carrying the alcohol to the station and for receiving the collection for transportation. Careful notes should be made on the spot of the conditions under which the species are found. One is likely to forget details if this is delayed until one reaches home. Labels should be used, giving name when known, or a number when the name is not known, [pg015] corresponding with the note-book. Names written with lead-pencil on a slip of paper will not be defaced by or injure the alcohol. Collections when arranged permanently should be placed in glass jars, the species being kept separate.

COLLECTING AND PRESERVING SEAWEEDS

To collect seaweeds one must search for them on rocks, in tide-pools, in the sea-wrack upon the beach, on piles of wharves, on eel-grass, and on the surface of incoming waves. It is well to follow the receding tide and take advantage of its lowest ebb (especially of that of the spring-tides, as mentioned above) to search the extreme limit of the beach in the short time it is exposed. Many of the red seaweeds are found there.

The equipment for collecting consists of a basket, two small tin pails, one small enough to be carried within the other, a staff with an iron edge at one end and a small net at the other, and a pocket-lens. Rockweeds (Fucus) or other coarse gelatinous seaweeds should be put into the basket. The pails, half filled with sea-water, will receive the other specimens, fine and delicate algæ being put into the smaller pail. It is well to have a second small receptacle for Callithamnion and Griffithsia, if one can be further burdened. Desmarestia should be kept apart, if possible, since it discolors and decomposes other algæ; it should also have the earliest attention when the time comes for mounting, and salt water should be used for floating it upon the mount, otherwise the beauty of the specimen will be impaired.

Besides its use as a support, the staff is needed to dislodge specimens from the rocks, and the net to secure those that are floating just out of reach. When possible, it is desirable to secure the whole plant, including the holdfast, and to gather several plants of the same species, since they vary with age and other conditions, and it is also well to have duplicates for exchange. It is particularly desirable to obtain plants which are in fruit. Each specimen as it is taken should be rinsed in the sea-water to free it from sand.

Collections should be mounted as soon as convenient, and [pg016] especial care in this respect should be taken with red algæ, as they decompose quickly. The requisites for mounting are blotters, pieces of muslin, two or more smooth boards, weights, a basin, and several shallow dishes containing water. Fresh water has a strong action on the color and substance of seaweeds, and specimens should not be left in it for any length of time.

Lift a specimen from the general collection, and in a basin of deep water carefully wash off all superfluous matter; then place it in shallow water and spread it out, trimming it judiciously, so that when mounted it will not be too thick and the characteristics be hidden. Specimens are more interesting and their species more easily determined when laid out rather thin, showing their branching and fruit. After the specimen is thus prepared, place it in a second shallow dish of water. It should now be perfectly clean. Float it out into the desired position, spreading it well, letting some parts show the details of the branching, and other parts the general natural effect of the mass. Run under it a rather heavy sheet of white paper, and lift it carefully from the water. If raised from the center, it is easier to let the water subside evenly and gradually without disarranging the parts. Some collectors find it better to float the specimen in water deep enough to allow the left hand to be placed under the sheet to raise it. Lay the sheet on a plate, and with a needle or forceps rearrange any of the delicate parts which have fallen together. A few drops of water placed on any portion will usually be sufficient to enable one to separate the branchlets or ultimate ramifications. A magnifying-glass will be useful in this work.

Cover a blotter with mounted specimens, spread over them a piece of cotton cloth, and on this place another blotter, upon which lay more mounted specimens and a cloth. Proceed in this way until all the specimens are used. Lay the pile of blotters between boards, and on them place the weights. The weights should not be very heavy. Judgment must be used in assorting the specimens, those that are fine being placed together. Those that are coarse and likely to indent the blotters should be placed between separate boards. In this way a flat surface and an even pressure will be obtained. The blotters and cloths should be [pg017] changed twice each of the first two days, then the cloths should be removed and the specimens left in press for a week, the blotters being changed daily. Be sure that the specimens are perfectly dry before placing them in the herbarium. Label each specimen with the name and the date and place of collection.

There are some seaweeds which cannot be treated in the above manner. Fucus if placed in fresh water soon becomes slimy. It is so full of gelatine that it soon destroys blotters; therefore it is well to hang it up for several hours and then place it between newspapers, which should be frequently changed, and as the plant becomes pliable it should be arranged in proper position.

Those specimens which do not adhere to paper in drying should be secured with gum. When it is impossible to mount specimens at the time they are collected, they can be preserved by drying; afterward they can be soaked and mounted in the usual manner. To dry the plants, lay them separately upon boards without pressing out the sea-water, and leave them in an airy, shaded place until thoroughly dry; then pack them loosely into boxes and label, giving date and locality. Blotters or driers can be obtained at botanical-supply stores at thirty-five cents per quire.

HOW TO ARRANGE A HERBARIUM

The standard herbarium-paper is sixteen by eleven and a half inches. The sheets are single, white, smooth, and quite heavy. These, together with folded sheets of yellow manila paper, called genus-covers, are the only requisites. It is desirable to have also a case of shelves protected by glass doors. The shelves should be twelve by eighteen inches, and four to six inches apart. They are more convenient when made to slide like drawers.

The different species of one genus are gummed on one or more of the white sheets and placed within the folded manila paper, which serves as a cover. Each specimen should be signed with its name, place, and date of collection, thus:

the generic name being indicated by its initial capital letter and the specific name written in full. To this are often added the [pg018] name of the collector and some interesting comment. On the lower left-hand corner of the genus-cover is written the generic name in full and the species of that genus which the cover contains, thus:

The genera of an order are then placed within a cover and labeled in the same way, the legend then having the name of the order on the left and the genera on the right of the bracket,[†] thus:

When the order is a large one the genera are distributed through as many covers as may be necessary. The covers are then arranged on shelves in the regular order of their classification, and each shelf is labeled with the order it contains. Herbarium-sheets cost at retail one dollar per hundred. Genus-covers cost at retail one dollar and eighty cents per hundred. [pg019]

III
CLASSIFICATION

The first great biological division is into kingdoms, namely, the animal kingdom and the vegetable kingdom. Then by classification the vast number of existing animals and plants are grouped so as to give each individual a definite place. By this system a beautiful order is established, which enables the student to find any particular animal or plant he may wish to study, and also to know its general characteristics from the name of the group to which it belongs.

In broad generalization, objects of wide dissimilarity are recognized as belonging to the same kingdom, as do trees and grasses, or as do birds and fishes. Certain trees or grasses and certain birds or fishes have such points of resemblance that they plainly show that they belong to subdivisions. The most untutored people recognize these distinctions, but the naturalist goes further and finds points of distinction which the casual observer overlooks.

The animal kingdom has a varying number of divisions, called branches, subkingdoms, or phyla. Some late authors have admitted twelve divisions, and have given them the name phyla. Each phylum is composed of a group of animals with a plan of structure which is common to themselves, but differs from that of the animals of all other phyla.

The higher animals begin with the twelfth phylum, namely, the Chordata, or vertebrates. These animals have a spinal column, or series of vertebræ, while the lower animals, or invertebrates are without a spinal column, and depend for stability [pg020] upon muscles or coriaceous or calcareous coverings. The vertebrates are first represented in the fish-like forms. Bilateral symmetry, however, or the uniform arrangement of parts on each side of a central axis, exists in several groups which are below the vertebrates, the first pronounced example being found in worms. Groups lower than worms have their organs arranged around a central axis or radiating from it, and were once all classed as radiates.

An animal is classified in accordance with its morphology, anatomy, histology, and embryology. Morphology determines its general shape, the position of its limbs, eyes, and mouth, and the covering of its body; anatomy, the arrangement of its internal organs, such as the position of its heart, lungs, stomach, etc.; histology, the character of the tissues of the body; and embryology, the method of the development of the animal from the embryo to maturity. It is only after these exact discriminations have been made that the groups are arranged. Owing to the greater accuracy resulting from histology and embryology (methods which have been employed only in later years), many changes in classification have been made, and as science advances will continue to be made.

The primary groups are based on broad general characteristics, but their divisions and subdivisions are determined by closer distinctions. Animals having shells differ from those having a cartilaginous or those having a crustaceous covering, and are placed in different groups. Yet mollusks having a single or a double shell, having spiral or flat forms, living on land, in fresh water, or in the sea, while differing from one another, are all of one group. Lobsters and crabs, although both have crustaceous coverings, are very unlike; and again, there are many species of both lobsters and crabs.

To group individuals, noting resemblances as well as differences, a system of classification has been arranged with the following divisions:

IV
ANIMAL LIFE IN ITS LOWEST FORMS

The biological division, or discrimination, between animal and vegetable life, is based on the manner of assimilating food. Plants feed upon mineral substances, or, in other words, assimilate inorganic matter, while animal life requires for its support vegetable or some other organic matter.

Animal as well as vegetable life in its lowest forms begins with one-celled organisms, which are called respectively Protozoa (first animals) and Protophyta (first plants). Both of these divisions are composed mostly of microscopic objects, and, together with other minute forms of life of the marine species, constitute a great part of the plankton, or free-floating organisms of the sea. These minute organisms seem like connecting-links between the two kingdoms. They were claimed by both botanists and zoölogists until the use of the microscope made close observation of minute structure possible.

Among the small animalcules of the phylum Protozoa are some which are familiar to all by name, such as the Infusoria, which are most interesting creatures to examine in a drop of water under the microscope. A more tangible example of the Protozoa are the Foraminifera. Foraminifera, like diatoms, have a shell-like covering, and these shells, among the most plentiful of which are those of the genus Globigerina, fall, as do those of diatoms, in immense numbers to the bottom of the ocean, and form respectively what are known as Globigerina and diatomaceous ooze. In course of time the sedimentary strata become fossilized; thus, the stone of which the city of Paris is built consists of fossilized [pg022] foraminifers, and the pyramids of Egypt are built of nummulites, another genus of Foraminifera. It is estimated that an ounce of this deposit contains four millions of these protozoans, so it is impossible to conceive the numbers of once living animals represented in the tombs of the Pharaohs. Telegraph-cables raised from the depth of two miles bring the message to naturalists that the bottom of the ocean at that depth is composed of little else than the calcareous shells of Foraminifera.

Many of the lower animals resemble plants in form. Hydroids and polyzoans are often gathered and preserved as seaweeds. Corals, sea-anemones, and holothurians are curiously like plants. For a time the confusion about the division of animals and plants was partly owing to this resemblance of forms, and the theory of the animal nature of corals was for a long time considered to be refuted by the testimony of a naturalist who declared that he had seen them in bloom. Later this class of animals was believed to occupy an intermediate sphere and partake of the characteristics of both kingdoms. The name zoöphyte, meaning "animal-plant" or "mingled life," was adopted because of these resemblances and was formerly applied to these forms only. To-day it has a broader application. There is still a neutral class, called Protista, comprising organisms which have not yet been classified as plants or animals. [pg023]

V
DISTRIBUTION OF ANIMAL LIFE IN THE SEA

All living things which inhabit the sea have their appointed boundaries, and the localization of marine life is as distinct as is that of terrestrial life. Each kind of beach has forms of life peculiar to itself. Those animals which inhabit rocky shores or stony beaches or sand or mud may be looked for anywhere under similar physical surroundings. They are, however, modified by climatic conditions, and in wide ranges differ in genera and species. The rocky coast of Maine has a class of sea-urchins and starfishes which are different from those which live on the rocky shores of the northern Pacific coast, yet they are all easily recognized as belonging to the same family, and a description of typical forms is a sufficient guide to the recognition of their relationships.

A bathymetrical division defines the classes of animals according to the depth of water in which they live. Those which live near the shore are littoral species, those of the broad sea are pelagic, while those living at great depths are abyssal.

Their modes of life are distinguished by other terms. Those which float at or near the surface and are carried about by the currents, like the jellyfishes and the minute organisms mentioned elsewhere, are plankton. Strong swimming animals which move about at will are nekton. Those which are fixed, like oysters, sponges, etc., and those which crawl on the bottom, like crabs, echinoderms, etc., are benthos.

Again, geographical divisions are named, in recognition of climatic influences. The boreal fauna and flora on the Atlantic [pg024] coast extend from Cape Cod northward; the American, from Cape Cod to Cape Hatteras; the West Indian, from Cape Hatteras southward. On the Pacific coast the divisions, without definite names, are from the Isthmus to Acapulco, Acapulco to the Gulf of California, Cape Lucas to the Strait of Fuca. These divisions merge at indefinite lines, but the above limits are generally accepted as the points of broad division.

The shore or littoral fauna is especially abundant and comprises more species that are curious in form and beautiful in color than the others. The invertebrates of the deep sea are mostly transparent and of a blue or violet tint, while the fishes are gray or bluish above and white beneath, which renders them inconspicuous to their enemies. [pg025]

VI
SOME BOTANICAL FACTS ABOUT ALGÆ

The vegetable world is separated into two great divisions: thallophytes, or plants having no distinction of leaf or stem, and cormophytes, or plants which have leaves and stems. All thallophytes that live in the water and are nourished wholly by water are called algæ.

A second great division of plants is into cryptogams, or those that have no flowers, and phanerogams, or those that have flowers, by means of which seeds are produced and successive generations of plant life continued.

Thallophytes and cryptogams comprise the lowest and simplest vegetable organisms. Algæ belong to both these divisions; to the first because they have neither stems nor leaves, and to the second because they have no flowers.

The lowest forms of algæ are microscopic in size, each individual being a single cell; but in the ascending scale they attain curious and beautiful shapes, some growing to a gigantic size and in forms that resemble shrubs and trees. The green surface commonly seen on the shady side of trees, on stone steps, and in other damp places is one of the species of algæ which consist of a single cell. This plant or cell divides, and the separate divisions divide and subdivide again and again, and in time the aggregate number is great enough to spread over a comparatively large surface, and thus become visible to the naked eye. This plant, the Pleurococcus vulgaris, is a fresh-water alga. The Protococcus nivalis, or red snow, described on page 33, is a closely allied species. The green and blue-green scums and slimes on [pg026] brackish ditches and on the stones and woodwork of wharves are also species of the lowest orders of algæ and increase by cell-division. Many of them are in colonies incased in gelatinous matter. These, together with plants of a little higher order, though still of low organization, the Confervaceæ, form a large part of the green vegetation between tide-marks.

The vegetative body of a thallophyte is a thallus, and corresponds to stem and leaf. It is also called a frond. What corresponds to the root of flowering plants is in algæ a disk or conical expansion of the base of the plant. It is simply a holdfast by which the frond attaches itself to any submerged material. The algæ which grow on sandy shores and on corals have holdfasts which branch like fibrous roots and penetrate porous substances in all directions; but this is only for greater stability, and is an adaptation to the habitat. Holdfasts do nothing for algæ other than the name implies, whereas real roots absorb the nourishment upon which plants live. Algæ are nourished by the substances held in solution by the water which surrounds them.

Algæ are the lowest and simplest in organization of all plants, because they are composed of but one class of cells, such as in flowering plants are called the parenchyma, or soft cells, these being the ones which compose the pulp of the leaf. In the lowest orders of algæ single cells constitute individual plants, as in Pleurococcus; but in the higher forms, such as Sargassum, they arrange themselves in such a variety of combinations as to resemble plants which have leaf and stem. The botanical distinction is that in leaf and stem there would exist the woody and the vascular cells as well as the parenchyma cells.

Beginning with plants composed of a single cell, the next development is into filamentous plants, which are single thread-like rows of cells, as in Cladophora. In Ulva is seen the earliest type of an expanded leaf. The cells are here arranged in a horizontal surface of plate-like or ribbon-like shape.

In Ulva there is a double layer of cells. The layers separate in Enteromorpha, giving a hollow or tubular form. In Monostroma a double layer is opened or torn apart, giving a frond with a single layer of cells. [pg027]

The stem-like forms of certain algæ are composed of cylindrical cells which combine or grow in a longitudinal direction chiefly. Sometimes the cells are arranged evenly, in which case the stem seems articulated, as in some species of Ceramium. Again, they are irregularly placed, so that the stem appears solid.

The highest types of algæ in the differentiation of parts, or vegetative forms, are to be found in the Fucaceæ, of the brown seaweeds; the highest in the reproductive development, in the red class.

Reproduction by cell-division, in which the organism itself breaks up into two or more individuals, is called vegetative reproduction. Higher forms reproduce by spores, or germ-cells, which give rise to new individuals on germination.

The substance of an alga is more or less firm, according as the vegetable mucus or gelatinous matter it contains has more or less consistency; it is membranaceous when the gelatine is scant and glossy, gelatinous when it is abundant and fluid, and cartilaginous when it is hard.

Some algæ are annuals; a few are perennials, and cast off and renew their laminæ every season. Many plants present quite a different appearance at different seasons of the year, and so are often difficult to identify. Those which form spores throw off these isolated cells, which sink or are washed to positions where they germinate and begin their cycle of life. Many of the spores begin their growth at once, without regard to season, so the species is ever present. [pg028]

VII
NAMING OF PLANTS

The real or technical names of plants, which at first appear long and unpronounceable, are in reality simple when the system of naming is understood. Every plant has a generic and a specific name. The generic name is analogous to the surname of a person, such as Smith or Jones. The specific name is analogous to the Christian name of a person, such as John or James. The specific name never stands alone, and would have as little designating character as John —— or James ——.

This is called the binomial (two-name) nomenclature. It was introduced by Linnæus, and greatly simplified the system of naming. The rule in scientific nomenclature is that all names must be Latin or Latinized. This gives a universal language by which scientists of all countries understand one another.

The names of classes (the highest groups) and subclasses are adjectives or adjective nouns, expressing the most prominent characteristic of the class or subclass. Thus the four subclasses of the class Algæ are:

Orders are, with few exceptions, the names of genera with the termination -aceæ, as:

Suborders, or groups between orders and genera, terminate in -eæ. Names of genera are nouns or words taken as nouns. They are derived from any source,—from prominent or peculiar characteristics, from localities, or from names of botanists,—or they may be wholly arbitrary. Personal generic names are divested of titles and take a final a, or, in many cases, for euphony, ia. Thus, Ulva is the Latin for "sedge"; Ectocarpus is from two Greek words meaning "fruit outside"; Corallina means "coral-like"; Grinnellia is named for Mr. Henry Grinnell.

The specific names are commonly adjectives, but sometimes they are nouns, and occasionally are the names of the botanists who first described the plants, in which case the name terminates in -i or -ii. The specific name always follows the generic name, thus:

Grinnellia Americana, a species, peculiar to America, of a genus named for Mr. Grinnell.

Griffithsia corallina, a species resembling coral, and belonging to a genus named for Mrs. Griffiths.

With regard to the four subclasses mentioned above, it should be said that algæ are strictly classified in accordance with their methods of reproduction; but since allied species have, with few exceptions, the same color, the classification by colors is generally adopted as convenient and sufficiently precise.

Familiar, or, in technical language, "vulgar," names are very generally given to land plants, and especially to flowers; but seaweeds are less in sight than flowers are, and so, save in a few instances, have not been named except by the man of science. To remember the scientific names will not be found difficult, for without effort or special pains to acquire the new vocabulary, the names, like those of new personal friends, will insensibly become fixed in the memory.

In the body of this work each of the groups (class, subclass, order, etc.), in the classification of both animals and plants, is indicated by a special kind of type. [pg030]

VIII
DISTRIBUTION OF ALGÆ

On the Pacific coast such distinct lines of demarcation do not exist, there being no such natural barriers as are formed on the eastern coast, first by Cape Cod, and, second, by the stretch of sand-beach which extends from New York to Charleston, and which divides sharply the climatic varieties.

The whole shore is again divided laterally into three distinct belts, called the littoral, the laminarian, and the coralline zones. The first or littoral zone covers the space between tide-marks. Vegetable life in this zone is subjected first to exposure to the sun and air, and even to desiccation, and then to entire submergence at constantly recurring periods. The rockweeds (Fucus), which are so plentiful in this zone, are very gelatinous, nature having apparently provided the gelatine to protect the cells of the plant from the effects of the alternating extreme conditions. Fucus and Enteromorpha predominate in this zone. [pg031]

The laminarian zone extends from low-water mark to the depth of fifteen fathoms. The Laminariaceæ and the beautiful red algæ (Florideæ) grow here.

The third or coralline zone extends to the depth of about fifty fathoms. The algæ of this zone, the nullipores, are incrusted with a deposit of lime which gives them the appearance of corals; and, singularly enough, the corals, which are animal forms, simulate plant life.

Again, algæ have special habits and demand certain climates and seasons for their growth. Algologists register the place where a specimen is found, and in this way localities have been pretty well determined. However, great exactness has not been reached, and the collector is ever watchful to find an alga in some undiscovered home within the given range. Although algæ grow from extreme high-water mark to the depth of fifty fathoms, almost every variety may be found on the beach, those growing in deep water being frequently torn off and washed ashore by the waves. The heaps of sea-wrack will often reward one who examines them carefully for deep-water species. Seaweeds are most abundant on rocky shores, particularly where there are stratified rocks with crevices, which afford shelter from the waves. Rock pools often contain beautiful varieties of the more delicate species. Red algæ will sometimes be found on the shady side of these pools. Sand-beaches are unfavorable to the growth of seaweeds, but fronds which have been carried long distances by the currents will frequently be found on such shores. [pg032]

IX
SOME PECULIAR AND INTERESTING VARIETIES OF ALGÆ

The species of seaweeds that are known and classified are said to number several thousands. These plants, which have neither vessels for the conduction of fluids, nor fibers, consisting simply of the first vegetable element, the cell, have, notwithstanding this limitation, assumed a great variety of forms. In size they vary from one one-thousandth of an inch in diameter, the smallest green plants known, to those which exceed in length the height of the tallest trees and form dense submarine forests, which in places make comparatively deep water impassable for boats. In texture they vary from a jelly- to a paper- and a leather-like consistency. In color they have all the shades of green, brown, and red.

DIATOMS AND OTHER MINUTE ALGÆ

Among the smallest algæ are diatoms. They are microscopic in size, but exist everywhere in both salt and fresh water, and are infinite in variety as well as in numbers. They have a silicious, shell-like covering, which divides and subdivides in their reproductive growth, forming varied shapes which are exceedingly beautiful and interesting to examine under the microscope. In vast numbers they float on the surface of the sea, and, together with other minute free-floating organisms, form the basis of food-supply for fishes. Their indestructible shells fall to the bottom of the sea, forming large deposits, which in time become fossilized. The city of Richmond, Virginia, is built upon [pg033] a fossiliferous bed of diatoms, which measures twenty to eighty feet in depth and several miles in length.

Associated with diatoms, in fresh water, are desmids, which are green in color and resemble the diatoms except in having a cartilaginous instead of a silicious covering. Another minute organism, Pyrocystis noctiluca, is luminous and is said to produce the beautiful phosphorescent effects seen in tropical seas. Trichodesmium is a little alga which periodically occurs in great numbers, giving the water a red appearance, as in the Red Sea, which is said to derive its name from this circumstance.

RED SNOW

In the high latitudes of the arctic regions, also on snowy mountains at altitudes where all vegetable life is supposed to be extinguished, there sometimes appears a redness on the surface of the snow, which in some cases extends for many miles. At a certain place in Greenland the color was so vivid that an arctic voyager named the locality the Crimson Bluffs.

The strangeness and almost sudden appearance of this color in the snow have been so unaccountable to uninformed observers that it has been ascribed by them to the falling of bloody snow and has been regarded with superstition. The redness is caused by the growth of one of the smallest of plants, the Protococcus nivalis. It is a simple one-celled alga containing protoplasm and endochrome (red coloring-matter). It grows by cell-division, the cell dividing into four, eight, or sixteen parts on a quaternary scale. Each part acquires a new covering while within the mother cell, and when it emerges it is a complete individual and ready to repeat the process. Only a few hours are required for its growth and development; hence its increase is rapid, and it requires but a little time to make itself manifest in those places where the conditions are favorable to its existence.

THE SARGASSO SEA

When the voyager reaches a certain region of the North Atlantic, called the Sargasso Sea, he sails into a vast undulating marine [pg034] prairie. Farther than the eye can reach is spread a yellowish-brown vegetation which covers the water as grass covers the plain. Sometimes these weeds are so thick as to impede navigation, and, seen from a little distance, seem substantial enough to walk upon. At other times, according to seasons and conditions of storm and wind, they are divided into strips or into island-like masses, with spaces of clear water between. If the sailor did not know the special conditions existing here he might suppose he had come upon dangerous shallows; or were the waters less turbulent he might dream that he was floating among the water-weeds of an inland lake.

This vast acreage of vegetation, as large as the continent of Europe, lying southwest of the Azores and extending between the Canary and the Cape Verde Islands, was first reported by Columbus, and takes its name from the floating plant of which it is composed, the Sargassum bacciferum, a species of the order Fucaceæ, commonly known as gulfweed. Columbus's sailors took fright at the marvelous appearance and wished to turn back, thinking they had reached the end of the navigable ocean. They thought, if land were beyond, it was guarded by shoals, and that the weeds concealed dangerous rocks. Columbus threw out two hundred fathoms of line, but did not reach bottom, and continued on his course for fifteen days before emerging into clear water. From that day to this the Sargasso Sea has attracted the attention of all navigators. It is especially interesting to scientists. The physicist finds there the phenomenon of the ocean currents holding in a vortex this immense mass of seaweed, the zoölogist finds a great pasture in whose protecting shelter are living and breeding countless numbers of marine animals, and the botanist is puzzled because the source of this species of plant is clouded with doubt.

PLATE II.
Macrocystis pyrifera.
Agarum Turneri.	Nereocystis Lütkeana.

According to one theory, the plants are dislodged by the tempests from terrestrial beds and carried by the Gulf Stream into the huge eddy; but since there does not exist enough of the attached plants of this species to supply the vast accumulation, another and more generally accepted theory is that the gulfweed lives also a pelagic life and adapts itself to the conditions of the [pg035] floating state, thus dispensing with the disk-like root, as it needs no holdfasts, and propagating solely by lateral and axillary ramification.

There are said to be one hundred and fifty species of Sargassum, but S. bacciferum alone constitutes the beds of the Sargasso Sea. The plant is the most highly differentiated of any seaweed, in that it more nearly approaches the true leaf and stem, and is described botanically as follows: Frond furnished with distinct, stalked, nerveless leaves and simple, axillary, stalked air-vessels. The integument is leathery, and the color brown of varying shades. The most striking peculiarity is the abundance of globular cells. These berry-like air-bladders give the plant buoyancy enough to support the weight of its innumerable guests. (Plate XVI.)

THE LAMINARIACEÆ

In the laminarian zone, described above, grow the Laminariaceæ, an order of brown seaweeds, some of whose genera grow to enormous size, and in some places form dense submarine forests. Darwin speaks of the good service rendered by these plants to vessels navigating stormy coasts, where often they act as natural breakwaters, and again as buoys designating dangerous rocks near the shore on which they grow. The seaweeds belonging to this order, commonly known as oarweeds, tangle, devil's-apron, and sea-colander, are frequently seen twelve to twenty feet in length, and others are measured by fathoms. One of the giant plants is Nereocystis Lütkeana, which occurs on the northwest coast. It has a stalk, sometimes three hundred feet in length, which bears on its extremity a barrel- or cask-shaped air-vessel, six or seven feet long, from the surface of which a tuft of fifty or more forked laminæ grows to a length of thirty or forty feet. The stem which anchors this immense frond is so small that the Aleutian Indians use it for fishing-lines. The sea-otter makes his home on its huge air-vessel, and the plant is called by the Russians the "sea-otters' cabbage."

But the longest of all known plants is the alga Macrocystis. Its thin naked stem, the diameter of which seldom exceeds one quarter [pg036] of an inch, is reported by one author to be seven hundred feet in length, by another fifteen hundred feet. It is terminated by a lamina fifty feet long, resembling a pinnatifid leaf, each leaflet of which, at its point of division on the stem, expands into an air-vessel as large as an egg. These air-vessels sustain the immense frond which floats on the surface of the water, its leaflets depending in a vertical position from the stem. M. pyrifera, the only species, is found in the Southern oceans and on the Pacific coast of North America.

Lessonia, another genus, resembles a palm-tree. It grows erect to a great height and has a stem like the bole of a tree. It branches in a forking manner and has depending from its branches laminæ two or three feet long. The large stems from which the laminæ have been torn by the storms, and which have been cast ashore on the Falkland Islands, as described by Sir Joseph Hooker, resemble driftwood, as they lie in piles three or four feet high and extending for many miles.

Agarum and Thalassiophyllum are arctic genera, but they are found within our limits, the former in the North Atlantic. It has a simple but enormous leaf-like frond. The latter, which is found on the North Pacific coast, has a compound frond. Both are characterized by their fronds being perforated throughout with holes, giving them the name of sea-colander. [pg037]

X
USES OF ALGÆ

Water covers two thirds of the surface of the earth, and algæ, with a very few exceptions, constitute the whole vegetation which exists in that enormous area. They have, therefore, an important part to perform in the economy of nature. Algæ do not, like land plants, derive their nourishment from the soil to which they are attached, but from substances held in solution by water. In their growth they effect changes in the water analogous to those effected by land plants in the air; that is, they change so-called impurities in the water into materials essential to animal life. The function of plants is that of transforming or manufacturing inorganic matter, which they assimilate, into organic matter (such as starch, albumen, sugar), which forms their own structure and which is the food essential to animals. In this process, plants inhale carbonic acid gas which animals breathe out, and exhale oxygen which animals breathe in. Plants feed on mineral substances and furnish vegetable food, thus keeping up the balance of life.

Fresh-water algæ have a like economic value. The green surface on stagnant pools is a vegetable growth whose function is to assimilate the matter which makes the pool offensive. A submerged district soon becomes covered with scum, or minute plants (Sphæoplea annulina), which grow with great rapidity, using up the materials of the decaying vegetation, and in great measure counteracting the ill effects, in the atmosphere, of such decay. When the waters subside, the plants shrivel up and appear like thin paper covering the ground. This ephemeral substance soon [pg038] disappears, without giving evidence of its nature in dust or gases, its body seeming to be a machine which transmutes, but does not hold, the substances on which it grows.

Algæ, as has been said above, grow in definite zones, and each zone has also a definite animal life which finds there its food. Darwin says: "In all parts of the world a rocky and partially protected shore perhaps supports in a given space a greater number of individual animals than any other station." And speaking of the Laminariaceæ, he adds: "I can only compare these great aquatic forests of the southern hemisphere with the terrestrial ones in the intertropical regions. Yet if in any country a forest was destroyed I do not believe nearly so many species of animals would perish as would here from the destruction of the kelp." The same may be said of the Sargasso Sea, where millions of living creatures make their home. In every kind of marine fauna there are species which derive, if not the whole, at least a part of their nourishment from the seaweeds.

The vegetation in the narrow boundary of the three zones is palpably inadequate to supply the needs of the animal life which exists in deeper waters. But over the broad area of the ocean there exists a vast number of pelagic, free-floating algæ, which, although microscopical in size, are almost infinite in numbers. In illustration of this it has been estimated that, although they are not especially numerous in the Sargasso Sea, yet if all the seaweed there were gathered into one mass and the free-floating algæ into another, the bulk of the latter would exceed that of the former. The pelagic flora consists of Diatomaceæ, Protococcaceæ, Peridinieæ, and others. Undoubtedly it is on these pastures that fishes feed, as well as other organisms which in turn are food for fishes.

Fucus and Laminaria constitute the kelp from which iodine is obtained, and were at one time the source of the potash of commerce. Fucus vesiculosus is a constituent of a medicine used as a cure for obesity. Chondrus crispus, commonly known as Irish moss, was a few years ago generally used as an article of diet. Porphyra vulgaris (laver) is used by the Chinese for soups. Rhodymenia palmata (dulse) is an article of food in Ireland and Scotland. [pg039] Gracilaria spinosa is used by birds, allied to the swallows, for making their nests—the edible nests found in large numbers on the islands of the Indian Archipelago, especially in the caves on the shores of Java, and gathered and sent to China, where they bring large prices and are used in making the famous birds'-nest soup. Gracilaria lichenoides, also a species of the Eastern seas, is the source of agar-agar, a preparation used in laboratories as a culture-medium for bacteria. Fossil diatoms are ground and used for polishing-powders. Seaweeds are everywhere used by farmers on the coasts as fertilizers. [pg040]

XI
COLLECTING AT BAR HARBOR

The beautiful coast of Maine is a particularly good field for shore-collecting. The rocky coast harbors the boreal fauna and flora which depend upon such physical conditions, and the shores at Bar Harbor are typical of those found elsewhere in northern New England. The rocks give shelter from the beating surf, while life has exposure to the cold, pure waters of the arctic current. Everywhere along the shore, rock pools are to be found. These are perhaps the most fascinating of all spots to the collector. They are veritable gardens of the sea, where species flourish which naturally belong to deeper water, but which find in such pools conditions suitable to their existence.

At Bar Harbor one well-known and frequently visited rock pool is found in Anemone Cave. Entering a field at Schooner Head, one turns to the right and follows the rocky shore for two or three hundred feet. It is difficult to take this short walk without being constantly diverted and delayed by the various attractions one meets, such as the tide-pools, the barnacles which in places whiten the rocks, the periwinkles, the purpura shells, and the curious algæ; but at last one arrives at a cavern under an overhanging rock. Here is a large tide-pool which at first sight displays only a beautiful scheme of color. It is carpeted with a bright-pink alga, Hildenbrandtia rosea, which incrusts the basin of the pool.

Interspersed with the pink are patches of a deep-red color, having a velvety appearance, which are formed by another crustaceous alga, Petrocelis cruenta. The water of the pool is of crystal [pg041] clearness, and as one gazes into it one object after another comes into view, until one is filled with astonishment at the number of beautiful objects the pool contains. The little green balls, one half of an inch to one inch in diameter, which look like small green tomatoes scattered on the stones, are Leathesia difformis, an alga which cannot be mistaken for any other. Bunches of Corallina officinalis, which resembles coral, as the name indicates, are abundant. This alga should be examined with a magnifying-glass. It is covered with calcareous matter, and its peculiar form of growth is beautiful and interesting.

The fronds of the laminarian Alaria esculenta are tiny here, while just outside the cave they are to be seen several feet in length, beating against the rocks in the swash of the waves. Thorny sea-urchins (Strongylocentrotus drobachiensis) make green spots which look like tufts of moss. Yellow and green sponges in little cones are spread over small surfaces. Starfishes and ophiurans are plentiful. The Purpura lapillus and Littorina litorea and rudis (periwinkles), so plentiful on this coast, are present. The Mytillus and the Saxicava and the Acmæa testudinalis are also to be found. A green crab (Carcinus mænas) is snugly hidden in a dark nook on the shady side of the pool, and many small crustaceans scuttle away from under stones as they are lifted. The collector is always anxious for uncommon, or rather less plentiful, species, and here are found two specimens of nudibranchs, or naked mollusks, Æolis and Dendronotus. The Chiton ruber, a jointed mollusk, was also found here, and five species of sea-anemones were counted. As this is a favorite hunting-ground, the anemones have not been left to attain full growth; but there are very many small ones which at first are not distinguishable, as they retract their tentacles at the slightest disturbance of the water and are then quite inconspicuous. After a little time of quiet watching they will be seen putting out their tentacles and expanding their beautiful flower-like forms. It is useless to try to capture them uninjured, so tightly do they adhere to the rocks, and the difficulty of preserving them in an expanded form is so great that amateur collectors had better leave them undisturbed to beautify the pool. [pg042]

It was hard to resist robbing this rock pool, where the author in half an hour counted twenty different species, and finally left, feeling that its treasures were not half discovered; but collecting should be done elsewhere, and this pool be guarded as a gem to be admired and not to be despoiled.

This pool in Anemone Cave, although so very attractive, is surpassed in beauty and interest by pools on Porcupine Island, at the base of the cliff. This place is somewhat difficult of access, and the timid will not undertake the descent to it; but the enthusiastic collector, who overlooks small obstacles, will be repaid by a visit to this spot, where all the treasures of Anemone Cave are multiplied many times over. These pools are resplendent with large anemones, hydroids, nudibranchs, mollusks, echinoderms, crustaceans, and algæ. Alaria esculenta, several feet in length, is beaten to a fringe against the rocks, and Agarum Turneri, the sea-colander, is also found here, together with beautiful specimens of Rhodymenia palmata, which is so plentiful that it reddens the rocks.

A Metridium marginatum, the most common sea-anemone of this coast, was taken here which measured six inches in diameter. This creature threw out so many of the processes used for defense that it seemed at first as though it were covered with some seaweed; but the worm-like movements of these threads, which measured six inches or more in length, soon disclosed their nature.

On the more accessible shores of Porcupine Island are found the naked mollusks (nudibranchs) Æolis and Dendronotus. Clinging sideways to the rocks just above high-water mark are many shells of Littorina rudis. They are fastened to the rocks by a glutinous deposit along the outer lip, and the peculiar exposure of the open end, as well as the position above tide-mark, indicates that this animal is undergoing transformation into a land species. Littorina palliata is abundant on the rockweeds (Fucus); some of the specimens are banded with yellow, and all closely simulate the seaweed on which they cling. Beautifully banded specimens of Littorina litorea are also plentiful. Among other shells which are abundant here as well as elsewhere on this coast are Purpura lapillus, Acmæa testudinalis, Buccinum undatum, Mya arenaria, and Mytillus edulis. [pg043]

Under the rockweeds in small pools and crevices are the polyzoans Bugula turrita and Membranipora pilosa, and the hydroids Sertularia pumila and S. argentea.

The seaweeds Rhodymenia palmata (dulse) and Desmarestia are plentiful; also beautiful worms, crustaceans, and starfishes.

A very interesting beach is found a few hundred feet south of Otter Cliffs, to which an easy descent is made if one follows a pathway leading to it through a grove adjacent to the drive. Here one will be interested in the study of numerous and beautiful rock pools.

Sea-urchins (Strongylocentrotus drobachiensis) seem to carpet some of them, having the appearance of mossy tufts. Beautiful pink and purple starfishes (Asterias vulgaris), brittle-stars (Ophiopholis aculeata), sea-cucumbers (Pentacta frondosa), sea-anemones, and crabs are abundant. If one lifts a stone the little crustaceans Orchestia and Gammarus will hurry away, and very likely an interesting worm or a nudibranch will be found. It is also most interesting to watch the barnacles, which are below the surface, reaching out their curled, feather-like feet in regular rhythmic grasping motions. The common mussels (Mytillus edulis), which in places blacken the shore, are beautiful under examination, and the silky network or byssus which forms the anchorage should be observed.

The rocks are hung so plentifully with Ascophyllum nodosum (rockweed) that its beauty is likely to be passed over unnoticed. On the Ascophyllum is growing in tufts Polysiphonia fastigiata; other seaweeds, Rhodymenia palmata, Chordaria flagelliformis, Desmarestia aculeata, Corallina officinalis, and Ceramium, are so abundant that one forgets to value them at the moment. Higher up on the beach the rocks are spotted with papery sheets, which, floated out in water, prove to be the beautiful purple Porphyra. A fine, dark colored, hairy scum on the rocks is Bangia fusco-purpurea. Sometimes one finds here fronds of Laminaria which have been washed ashore. Various green algæ are abundant. Even if not collecting, it is well to carry a small tin pail to the beach and float out pieces of the algæ in order to observe carefully, if but for a moment, the beautiful forms they have in their natural state. Watched for a few minutes in a pail of water animals disclose curious [pg044] and surprising forms and habits which are difficult to watch leaning over a pool.

Most of the various species mentioned above are common along the whole shore, and may be looked for at almost any point where the water is free from contamination.

At the sand-beach are found species which do not inhabit the rocky shore, as the sand-dollar (Echinarachnius parma), Polynices (Lunatia) heros, Mya arenaria, and others. After a storm various deep-water forms are washed upon this beach. Laminaria digitata, six feet long, is found here sometimes under these circumstances. Chordaria flagelliformis, resembling long switches of hair, floats from the rocks near the shore. To the left, on the rock under the overhanging ledge, is a tide-pool which one would hesitate to deface by touching a single specimen. So crystal-clear is the water, so brilliant the Hildenbrandtia, so lovely the Corallina, that all seem placed there to excite admiration.

But most of all one should obtain the permission of the owner to visit Rodicks Weir. Here is an immense natural aquarium, full of living wonders. On a clear day, sunlight penetrates to the bottom, and at low tide the whole contents of the weir are clearly seen as one floats through the inclosed water-spaces. On the bottom are sea-urchins, many of them with sticks or stones on their backs, which the animals have placed there in the endeavor to conceal themselves; starfishes feeding; and great numbers of whelks (Buccinum undatum). Cuttlefishes dart rapidly about, and skates, sculpins, and other fishes display their curious forms. Very likely a giant jellyfish (Cyanea arctica) is entangled in the brush, so that one can examine at short range its wonderful and beautiful parts. Other jellyfishes may be closely scrutinized.

On the eel-grass are to be found Lacuna vincta and the delicate iridescent little shells of Margarita helicina.

Every tide brings different species of the ocean fauna to temporary imprisonment in this inclosure, so that it is difficult to say what one may not chance to find in this interesting place.

Part I
MARINE ALGÆ

BLUE-GREEN SEAWEEDS

The minute algæ, which form patches of purple color on rocks, slimy layers or spots on wharves, bluish-green slime on mud, emerald-green films on decaying algæ, blue-green slime on brackish ditches, and so on, are various species of the subclass Cyanophyceæ. The prevailing color of these plants is blue-green, but some are purple, brown, or pink. Some of them are gelatinous in texture and shapeless, others have more definite forms; but all are too small to classify without the aid of a powerful glass, and are not of special interest except to the botanist.

The genus Oscillaria is so named from an oscillating movement which these filamentous plants show when viewed under the microscope. They are very delicate blue-green threads occurring singly, or in loose or felt-like floating masses, or like slime or scum, on mud or woodwork. In Spirulina the filaments are spirally twisted like a corkscrew and also have a vibrating movement. Spirulina is often found growing with Oscillaria, and forms purple patches on wharves.

Filaments one tenth of an inch long, terminating in transparent hair-like points, occasionally branching. The plant grows in fine tufts or like a fringe on algæ or in patches on rocks. Sometimes it forms a spongy layer, again a velvety stratum. The color varies in different species; it may be bright green, brownish-green, [pg050] or dark bluish-purple. The genus is very common, and the plants are often found on the bottoms of boats.

GRASS-GREEN SEAWEEDS

"There can hardly be a more fascinating group of plants than this, whether to the strictly scientific botanist or to the more catholic lover of nature. The green algæ are among the most widely diffused of plant forms. They grow practically in every place where enough moisture, together with light and air, is to be had. Between tide-marks on almost every coast, floating on the surface of the deep sea, covering damp earth, walls, palings, and tree-trunks, sticking to the surface of leaves in the moist atmosphere of tropical forests and jungles, and inhabiting almost every river, brook, pond, ditch, or casual pool of rain-water in all quarters of the globe, are members of this ubiquitous group to be found."[3]

The grass-green seaweeds are more simple in structure, and therefore are lower in order, than the red or brown algæ. They are among the lowest of all plants, many of them being minute single cells. They abound in fresh as well as in salt water, and in this respect differ from the other groups, the red and the brown algæ being almost exclusively marine plants.

As one approaches the shore, the attention is often attracted by the green mantle which covers everything overflowed by the tides. This consists largely of the confervoid algæ, which are very abundant and are found almost everywhere. They are dense tufts of fine thread-like plants, often matted at the base; sometimes they are sponge-like, floating masses.

The Ulvaceæ, the plants next higher in order, are the first which assume ribbon- and leaf-like expansions, and usually first engage the attention of the collector. [pg053]

In the green algæ are found the extreme forms of one-celled plants. In Pleurococcus the cell is microscopic in size. In the Siphoneæ the plant still consists of a single cell, but it attains large dimensions and develops into forms resembling, in outward appearance, leaf, stem, and root (see Caulerpa).

Other plants consist of single rows of cells, called filaments (Confervaceæ), or of cells arranged in layers or flat surfaces, called membranes (Ulvaceæ).

ORDER CONFERVACEÆ

The silkweeds. This order is characterized by cylindrical cells strung end to end, forming threads or filaments, branched and unbranched. The plants inhabit both fresh and salt water, and are very abundant and widely distributed. They grow in dense tufts, often matted at the base.

A yellow-green, unbranched, decumbent, soft, hair-like fleece on the surface of rocks, extending indefinitely. This genus differs from Chætomorpha in the character of its filaments, which are soft and gelatinous in Ulothrix, but bristle-like and wiry in Chætomorpha.

The frond is filiform; the filaments are coarse, rigid, and unbranched. In some species the filaments grow straight and in tufts from a definite base; in others they are twisted together and are prostrate. Often they are found floating in masses. In C. tortuosa the filaments are as fine as human hair, but rigid, and so closely interwoven as to resemble a layer of wool on the rocks. The cell-divisions give a striped appearance to the filaments when dry.

Frond filiform, branched. There are many species of Cladophora, which differ from one another in their branching, color, and size. They abound on rocks at low-water mark, in tide-pools, in muddy ditches, and on wharves. They are especially characterized by being so profusely branched as to form tufts or spherical masses, by which the collector can easily distinguish the genus.

PLATE III.
Chætomorpha melagonium.	Chætomorpha linum.
Cladophora arcta.	Cladophora rupestris.

PLATE IV.
Cladophora gracilis.	Ulva lanceolata.
Ulva lactuca, var. rigida.	Enteromorpha clathrata.

ORDER ULVACEÆ

The plants of this order are, with few exceptions, formed of celled surfaces and show the earliest type of an expanded leaf. The cells form thin membranes, which sometimes are broad surfaces of no definite shape, sometimes are narrow and ribbon-like, or they may be simple or branched tubes. When the membrane [pg055] consists of a single layer of cells it is Monostroma ("one layer"); when it consists of a double layer it is Ulva; when the layers separate, the thallus becomes hollow, and it is then Enteromorpha. These plants are mostly a brilliant grass-green in color, are silky in texture, and are attached by a small disk to rocks and stones. They abound everywhere, and are commonly known as green laver.

Frond a thin, silky, flat membrane, sometimes leaf-like, again an extended surface of no definite shape. These are the largest green algæ. They are common everywhere.

Fronds tubular, simple or branched, sometimes inflated. The tubes vary in size in different species and also in the same species, some being fine like a hair, others large, and flat or inflated. The genus is widely distributed and very abundant. Species of Enteromorpha grow on the bottoms of ships, and in nautical language are called grass.

This genus resembles Ulva, but is more delicate since it has but one layer of cells, as its name implies. The frond is usually sac-like at first, then breaks apart, leaving a thin, semi-transparent membrane of no definite shape.

GROUP SIPHONEÆ

The distinct and peculiar character of this group is that in each individual the whole plant consists of but one cell. There are many genera, some of which are plants of elaborate form and considerable size, but always the one cell expands and branches without dividing the elongated cavity with septa, or plates of division. In Caulerpa the stability of the plant is secured by numerous fibrils which emanate from the interior of the cell, forming a spongy network of interlacing filaments. In other orders the branches gain support from incrustation, from interlacing, and from cohering on the edges.

ORDER VALONIACEÆ

The algæ of this order are found only in tropical or subtropical waters. Their holdfasts resemble fibrous roots and penetrate the sand or coral on which they grow.

PLATE V.
Enteromorpha compressa.	Enteromorpha intestinalis.
Enteromorpha intestinalis.	Anadyomene flabellata.

PLATE VI.
Acetabularia crenulata.	Dasycladus occidentalis.
Penicillus dumentosus.	Udotea conglutinata.

ORDER DASYCLADACEÆ

This order also inhabits only tropical or subtropical seas. It is placed in this group, although only the main axis is unicellular. The one-celled axis is surmounted or encircled by whorls of minute filaments or branchlets (ramuli), which protrude through small holes and are either persistent or deciduous. In the latter case the fallen filaments leave disk-like scars on the stem.

Fronds destitute of calcareous matter, soft, cylindrical or club-shaped; single unicellular axis, beset with fine filaments or ramuli.

ORDER UDOTEACEÆ

This genus resembles the corallines externally, and is abundant on coral reefs. It appears as if formed of separate parts, resembling a series of heart- or kidney-shaped segments strung together. The plants are more or less incrusted with lime. The branching holdfast grasps particles of sand, and with them forms a solid ball.

PLATE VII.
Halimeda tuna.	Halimeda tridens.
Bryopsis plumosa.	Codium tomentosum.

PLATE VIII.
Caulerpa Mexicana.	Caulerpa Wurdemanii.
Caulerpa plumaris.	Caulerpa paspaloides.

ORDER CODIACEÆ

There are said to be about twenty species of this genus. They are distinguished by the manner of branching, but are not very definitely marked. All are erect, one-celled, branching stalks, and are feather-like in appearance.

ORDER CAULERPACEÆ

Caulerpa is the only genus of its order, but it contains about a hundred species, many of which resemble mosses, ferns, or cacti. Each plant is composed of a single cell, however much it may be [pg060] ramified. The frond consists of a prostrate stem, from the lower side of which root-like fibers or holdfasts descend into the hard sand or coral, and from the upper side leaf- and branch-like secondary fronds arise. These plants grow luxuriantly in tropical waters, extending over large surfaces, and are the chief food of turtles. (Plate VIII.)

OLIVE-GREEN AND BROWN SEAWEEDS

This subclass contains some of the most remarkable of the seaweeds. It is especially notable for the diversity of its plant forms, which range from filaments to plants which appear to have stems and leaves (Sargassum). The species vary in size from very small fronds to those of immense size (the Laminariaceæ). It includes Fucus (the rockweeds), a very conspicuous genus, which furnishes fully three fourths of the vegetable covering of the tidal rocks in the localities in which it grows.

ORDER ECTOCARPACEÆ

This order comprises many species of branched, filamentous plants, some of which are of hair-like fineness and form beautiful feathery tufts of brownish or olive-green color. They resemble, except in their tawny color, the green alga Cladophora.

The name is derived from Greek words meaning "outside" and "fruit," the spores of the plants being borne on the branches.

The species are determined by the arrangement of the spores, according as they are in the pod-like branches, in groups, or in cases on stalks. Since these differences are not perceptible to the naked eye, it is impracticable to describe many species, or for the amateur collector to try to separate them.

ORDER SPHACELARIACEÆ

ORDER RALFSIACEÆ

The species of this genus are brown, leathery, crustaceous expansions of indefinite form, one inch to six inches in diameter, resembling lichens. They appear on rocks in shallow, exposed pools.

ORDER ENCŒLIACEÆ

Dotted-weeds. Fronds pale olive-green, membranaceous, leaf-like, with short stem; covered with spores which appear like dots.

This genus differs from Punctaria in having a tubular instead of a flat frond. (Plate IX.)

ORDER DESMARESTIACEÆ (Named for M. Desmarest, a French naturalist)

PLATE IX.
Ectocarpus littoralis.	Ectocarpus viridis.
Cladostephus verticillatus.	Asperococcus bullosus.

PLATE X.
Phyllitis fascia.	Desmarestia viridis.
Desmarestia aculeata.	Desmarestia ligulata.

ORDER DICTYOSIPHONACEÆ

ORDER ELACHISTACEÆ

The plants of this genus are small, olive-colored, unbranched, hair-like filaments, growing in dense, radiating tufts, one half of an inch in height, on Fucus. They are interesting to the microscopist, but not to the collector.

ORDER CHORDARIACEÆ ("Cord-like")

This singular alga resembles a tuber and cannot be mistaken for any other plant. Its fronds are gelatinous, fleshy balls, one half of an inch to two inches in diameter, at first solid, afterward lobed and hollow. It grows singly or in bunches on algæ and on sand-covered rocks, and is found in summer on every coast. The common species is known as L. difformis or L. tuberiformis.

Minute algæ which grow on other plants and which appear like dark spots, or, at first, like stains, on Ulva, Enteromorpha, and small red algæ. These spots, which to the naked eye appear like decay, show, under the microscope, a jelly-like substance full of beaded filaments.

ORDER LAMINARIACEÆ

The plants of this order have large and coarse fronds (some attaining an immense size), with stems, branching root-like holdfasts, and expanded leaf-like laminæ. They are leather-like, not articulated, olive-green or brown in color, and sometimes yellow and semi-transparent. They grow in deep water and are found washed ashore. Sometimes small plants are found in deep tide-pools at low-water mark. Some species are perennial. In these instances the stems only survive, and the laminæ are reproduced annually. The new growth takes place at the apex of the stem. The old lamina is pushed off, but is held on the summit of the new growth until the latter has matured.

PLATE XI.
Dictyosiphon fœniculaceus.	Chordaria flagelliformis.
Mesoglœa virescens.	Mesoglœa divaricata.

PLATE XII.
Chorda filum.	Agarum Turneri.
Alaria esculenta.	Laminaria saccharina.

In the genus Chorda the fronds are cylindrical; in Agarum [pg069] the laminæ are perforated; in Alaria there are wing-like leaflets below the laminæ.

The Laminariaceæ and Fucaceæ are the seaweeds used in making kelp. For this the algæ are burned, and the ash is then separated into its different mineral constituents and used for various manufacturing purposes.

This genus is readily distinguishable by the fact that it has leaflets below the lamina. It is found north of Cape Cod.

The plants of this genus are all large, varying from one foot to twelve feet or more in length. They are of wide geographical range, and are more numerous in species than any others of the order. They are commonly known as oarweeds, tangle, devil's-aprons, sole-leather, kelp, sea-furbelows, and so on.

For the genera Macrocystis, Nereocystis, Lessonia, and Thalassiophyllum, see the Introduction, pages 35, 36.

ORDER DICTYOTACEÆ

PLATE XIII.
Laminaria digitata.	Dictyota dichotoma.
Taonia atomaria.	Padina pavonia.

PLATE XIV.
Haliseris polypodioides.	Cutleria multifida.
Fucus vesiculosus.

ORDER CUTLERIACEÆ

ORDER FUCACEÆ

The rockweeds. The plants of this genus grow in thick bunches, and are found in great abundance between tide-marks. The plants are attached by sucker-like disks to the rocks, from which they hang like fringe when the tide recedes; when it rises they float and sway in the water in beautiful bouquet-like forms. In color they are brown or olive-green, in texture thick and leathery, but they sometimes expand into thin membranes. They are many times forked in the same plane, which produces a flat thallus. They often have a distinct midrib. The air-vessels, whose function it is to float the plant, are disposed along the midrib, usually in pairs.

The species are named according to the divisions of the frond, and the disposition, or presence, of the air-bladders and the conceptacles, or spore-chambers.

The conceptacles congregate in particular portions of the frond and give its surface a roughness which is very perceptible; such portions are then known as the receptacles. In Fucus this usually occurs on the bulbous extremities of the branches. Under the microscope a section of one of these little pointed spots shows a spherical cavity filled with a beautiful arrangement of paraphyses, or threads, some of which hold spores, while others protrude through a small opening in the outer membrane. Conceptacles are peculiar to the order Fucaceæ. In them spore-production is carried on in a manner as complicated as is the formation of seeds in flowering plants. Although rockweeds are such a conspicuous feature of sea-shore vegetation, two species only, Fucus vesiculosus and Ascophyllum nodosum (formerly called Fucus nodosus), are common on the Atlantic coast, and these do not occur south of New York, owing to the fact that a long stretch of sand-beach extends beyond that point.

PLATE XV.
Fucus serratus.	Fucus ceranoides.
Ascophyllum nodosum.

PLATE XVI.
Phyllospora Menziesii.	Halidrys osmunda.
Sargassum vulgare.

Sargassum is distinguished by its differentiation into stem and leaf, resembling in outward appearance the higher plants. It [pg074] is a tropical and subtropical genus, and has one hundred and fifty species. Two of these, S. vulgare and S. Montagnei, are found as far north as Cape Cod. See Introduction, page 34.

RED SEAWEEDS

In Rhodophyceæ, known also as Florideæ and Rhodospermeæ, algæ attain their highest development. This is marked by the mode of reproduction, which, more nearly than in the other subclasses, resembles that of flowering plants. The fronds, however, are not as large and do not as closely resemble stem and leaf as do some species of the brown algæ.

The species of this subclass are very numerous, and the variety in their fronds, their delicate texture, and their colors, which vary from pink to purple, make them the most attractive of the seaweeds. They grow mostly in deep water, but are often found washed ashore, and many grow just below low-water mark and on the shady side of tide-pools.

In the simplest species the frond consists of branched cell-rows. In some of these the filaments are so fine that a pocket-lens is required to determine the differences in branching and fully to appreciate the beauty of the plant (Callithamnion). Some have a cell-surface. In Delesseria the membrane assumes the outline of a foliage-leaf. Dasya, which is an abundant variety, is especially beautiful in its feather-like appearance. The corallines are singular in that they are incrusted with lime and resemble corals.

ORDER NEMALIONACEÆ

Suborder HELMINTHOCLADIEÆ

Fronds filamentous; branching regularly in a forking manner to the very top, forming thick bunches; slightly incrusted with lime, yet somewhat viscid. It is found in Florida and California, and abounds in tropical waters.

Suborder CHÆTANGIEÆ

Suborder GELIDIEÆ

PLATE XVII.
Scinaia furcellata.	Gelidium corneum.
Gelidium Coulteri.	Chondrus crispus.

ORDER GIGARTINACEÆ

Of the species of this genus but one is found on the eastern coast; on the Pacific coast there are several, and they are large and conspicuous.

PLATE XVIII.
Gigartina mamillosa.	Gigartina radula.
Gigartina spinosa.	Gigartina microphylla.

Leafweed. Fronds cylindrical; branched stalks which expand into rigid, membranaceous, simple or cleft, wedge-shaped laminæ; laminæ bear leaflets on their edges or on their surface; spores in masses form projections on the surface, or are on stalks at the summit; color dark red. Found washed ashore from New York northward. [pg082]

PLATE XIX.
Phyllophora Brodiæi.	Sternogramme interrupta.
Gymnogongrus Norvegicus.	Ahnfeldtia plicata.

PLATE XX.
Callophyllis variegata.	Callophyllis laciniata.
Iridæa.	Cystoclonium cirrhosa.

Frond rises from stalk and widens into a flat, thick, leathery, oval expansion, one to two feet long, and one to three inches broad; [pg083] simple or lobed; surface sometimes roughened by collections of spores in dots; dark red, often glittering in the water with blue and purple tints. It is found on the Pacific coast. (Plate XX.)

Suborder RHODOPHYLLIDEÆ

ORDER RHODYMENIACEÆ

Suborder SPHÆROCOCCEÆ

PLATE XXI.
Euthora cristata.	Rhodophyllis veprecula.
Rhabdonia tenera.	Gracilaria multipartita.

PLATE XXII.
Rhodymenia palmata.	Rhodymenia palmata.
Lomentaria Baileyana.	Chylocladia articulata.

Suborder RHODYMENIEÆ

Suborder DELESSERIEÆ

PLATE XXIII.
Champia parvula.	Champia parvula, magnified.
Plocamium coccineum.	Nitophyllum laceratum.

PLATE XXIV.
Nitophyllum Ruprechteanum.	Nitophyllum punctatum.
Grinnellia americana.	Delesseria sinuosa.

PLATE XXV.
Delesseria alata.	Delesseria Leprieurii.
Polysiphonia fastigiata (on Ascophyllum).	Polysiphonia parasitica.

PLATE XXVI.
Polysiphonia dendroidea.	Polysiphonia dendroidea, a piece magnified.
Polysiphonia Harveyi.	Polysiphonia Harveyi, a piece magnified.

Suborder RHODOMELEÆ

The genera included in this suborder are easily distinguished when in fruit by the spore-cases, or cystocarps, which appear [pg087] like little balls, either adherent to the branches, or raised on short stalks. It is the largest group, and contains many of the most beautiful of the red algæ.

A filament of Polysiphonia appears, when seen under the microscope, like a bundle of filaments made up of a central tube, or axis, surrounded by a number of other tubes. It is by the number of these parts, called siphons, which vary in number from four to twenty, that the species is determined. In some plants the siphons are surrounded by a layer of cells, called corticating or bark cells, which give the filaments a solid, uniform appearance. In others the siphons are naked, and the filaments then seem striped or banded with color. It is difficult, without a microscope, to be sure of the classification. There are, however, other characteristics which separate many of the species, and some of these are described below. Two hundred species of Polysiphonia have been named by algologists. The plants are plentiful on all shores, especially in warm, shallow waters. Some species are perennial, but most of them are annuals and disappear in winter.

Plants of this genus are distinguished by having the ultimate branches attenuated at the base.

PLATE XXVII.
Polysiphonia nigrescens.	Polysiphonia fibrillosa.
Polysiphonia violacea.	Polysiphonia Woodii.

PLATE XXVIII.
Laurencia pinnatifida.	Dasya elegans.
Dasya plumosa.	Dasya plumosa, magnified.

Suborder CERAMIEÆ

These are very beautiful and delicate plants, growing in small, soft, silky tufts, bright red in color, with darker dots along the much-branched filaments. There are many species, and they are common on the northern shores of both oceans; but the different species are not easy to distinguish with the naked eye, and so but a few of them are described below. The special characteristics by which the genus may be recognized are: fronds filamentous, of cobweb fineness, one inch to six inches long, much branched, and closely crowded at the top; brilliant red color.

These are among the most beautiful of seaweeds, because of their brilliant color and exceedingly delicate structure. They grow in deep water, and specimens cast ashore are usually torn and imperfect, but they may often be gathered from deep tide-pools, and sometimes are found growing on eel-grass. If placed in fresh water they discharge their coloring-matter and quickly decompose.

The pitcher-weed. This genus is easily recognized by the ends of the filaments, which are forked and incurved, resembling minute pincers or claws. The filaments are also more or less distinctly banded. It is widely distributed.

PLATE XXIX.
Bostrychia rivularis.	Rhodomela Rochei.
Rhodomela larix.	Rhodomela floccosa.

PLATE XXX.
Chondria dasyphylla.	Callithamnion americanum.
Callithamnion Pylaisæi.	Callithamnion Pylaisæi, a piece magnified.

PLATE XXXI.
Callithamnion americanum, a piece magnified.	Callithamnion seirospermum.
Callithamnion byssoideum, var. fastigiatum.	Callithamnion floccosum.

PLATE XXXII.
Griffithsia Bornetiana.	Ptilota serrata.
Ptilota serrata, magnified.	Ptilota elegans.

PLATE XXXIII.
Ptilota densa.	Ptilota hypnoides.
Ptilota hypnoides, magnified.	Spyridia filamentosa.

PLATE XXXIV.
Ceramium rubrum, var. proliferum.	Ceramium rubrum, top of frond magnified.
Ceramium diaphanum.	Ceramium tenuissimum, var. patentissimum.

ORDER CRYPTONEMIACEÆ

Suborder GLOIOSIPHONIEÆ

Suborder GRATELOUPIEÆ

PLATE XXXV.
Microcladia Coulteri.	Microcladia Coulteri, magnified.
Microcladia borealis.	Prionitis lanceolata.

PLATE XXXVI.
Prionitis Andersonii.	Pikea Californica.
Halosaccion ramentaceum.	Polyides rotundus.

Suborder DUMONTIEÆ

Suborder RHIZOPHYLLIDEÆ

Suborder SQUAMARIEÆ

Suborder CORALLINEÆ

The genera of this suborder are characterized by a calcareous or stony incrustation of the fronds, which gives them the appearance of corals. Most of the species are tropical. [pg096]

This genus will attract attention, although it cannot be gathered. It is a thin, brittle, scaly substance of indefinite form, which expands horizontally and resembles a lichen. It forms brown and pink crusts on other algæ and on rocks, stones, and shells.

ORDER BANGIACEÆ

This plant, except in color, is like the green alga Ulva. In color it is purple of various shades. The species are named from variations in the outline of the frond. They are found everywhere, and throughout the year. The plants are edible, being the laver of commerce, eaten principally by the Chinese, who make them into soup.

PLATE XXXVII.
Corallina officinalis.	Bangia fusco-purpurea.
Porphyra vulgaris.	Porphyra laciniata.

SPONGES

There are many animals which consist of but one cell. These are called Protozoa, and comprise the Infusoria and other microscopic organisms. The animals next higher in the scale are Metazoa, or multicellular animals, and the first group of this subdivision is Porifera, the sponges, the lowest of the many-celled animals.

For a long time sponges occupied a disputed ground between the animal and vegetable kingdoms. Aristotle was the first to point out that a sponge is not a plant. The assertion was doubted and combated, but at last the animal nature of the sponge was established. Sponges were then believed to be colonies of one-celled animals, but finally it was decided that they were individuals with cells of different kinds that performed functions analogous to those of higher organisms.

The sponge, as commonly seen, is only the skeleton or framework, so to speak, of the living animal. In its natural state it is a very different-looking object. Its entire surface is covered with a thin slimy skin, usually of a dark color, which is perforated with holes corresponding to the apertures of the canals. The organic portion of the sponge is a soft, jelly-like substance composed of three layers—the external (ectoderm), the internal (endoderm), and the middle (mesoderm). The external layer is composed of flat cells. The endoderm has cylindrical cells, each one of which has a flagellate hair. The main mass of the body, the mesoderm or middle layer, is made up of cells having various functions, some being concerned in the formation of framework, some in digestion, and some in reproduction.

The framework is secreted in the mesoderm, and in different [pg102] genera consists respectively of a horny or silicious or calcareous substance, or of the first two of these substances combined. The sponge of commerce has the first kind and is composed entirely of exceedingly fine flexible fibers of a horny substance called spongin. In other species the spongin is intermixed with spicules of silica, or of carbonate of lime, in various shapes. In the sponges, so much valued as curiosities, called "Venus's flower-basket" and "glass-rope sponge," the framework is composed of silicious spicules alone.

The spicules have a great variety of shapes, being rod-like, knobbed, three-pointed, six-pointed, anchor-like, etc., and are a feature in the classification of sponges.

The sponge is traversed throughout by a canal system, consisting of a series of tubes through which water circulates, carrying air and food to the animal. The exterior of the sponge has numerous small pores and a comparatively few large openings. The fine pores are inhalent, taking in and straining the water of its coarser floating material, and then passing it through perforations in their sides into sacs lined with peculiar cylindrical cells having flagellate hairs, each hair having a collar at its base. These cells, called choanocytes, resemble independent animals of the Protozoa, known as flagellate Infusoria or Choanoflagellata. [pg103] They take in and digest food and eject excrement from the area inclosed by the collar. The cilia (hairs) by their constant movement create currents which keep the water in motion. Water, then, is taken through the pores into the first or incurrent canals; thence it is passed into the ciliated chambers, and thence into the excurrent canals, and out through large passages terminating in large openings called oscula, or craters. The canal systems vary. In some species they become quite complex.

Sponges vary greatly in shape, size, color, surface, rigidity, canal systems, and skeleton. They are cake-shaped, tubular, digitate, palmate, cup-shaped, vase-shaped, cone-shaped, spherical, hemispherical, pedunculate, etc., their shapes depending upon whether their growth is uniform or is excessive in a horizontal or in a vertical direction. When they grow evenly in both directions massive uniform shapes arise. If lateral growth predominates, broad, low, and incrusting shapes result. When there is an excess of vertical growth the forms are digitate; [pg104] but if vertical growth is not greatly in excess and is restricted to the marginal part, cup-shaped forms result, and tubular forms when lateral growth is particularly restricted. In some varieties tubular masses coalesce; sometimes flat forms unite in intricate compressed folds. Differences in rapidity of vertical growth make undulations more or less marked, producing lobes and protuberances. Sometimes narrow vertical growth is retarded and horizontal growth predominates, forming various shapes on apparent stems.

Many of the horny sponges are colored, in shades of yellow, brown, red, and violet; some are black.

Sponges are divided into two classes, the Calcarea and Non-Calcarea. The former have calcareous skeletons, which make them hard and rigid; the latter have skeletons of spongin-fiber or of silicious spicules, or of the two combined.

All sponges, with the exception of one family (the Spongillidæ, which live in fresh water), are inhabitants of the sea, and live at various depths. The sponges of commerce belong to the Non-Calcarea and are all confined to the genus Spongia. In this genus the skeleton is more or less flexible, being composed of spongin. They are shallow-water species, are confined to seas where the waters are of comparatively uniform high temperature, and flourish best when protected by reefs and islands.

There are fisheries for sponges in the waters of the West Indies, the Bahamas, on the southern and western coasts of Florida, and in the Mediterranean and Red seas. Those of the Mediterranean surpass in quality the sponges of our coasts.

Five species of commercial sponges are taken from Florida waters. They are graded by the trade in the order of their importance, as the "sheepswool," "yellow," "grass," "velvet," and "glove." The fishing for sponges is done from small boats, two persons manning each boat. One man sculls, while the other, using a water-glass, scans the bottom. The water-glass is a box with a pane of glass on the bottom. If the glass is held below the surface and the face is placed in the box, the observer is enabled to see with some distinctness the bottom at a considerable depth [pg105] in these clear waters. The sponges are dragged up by hooks—a primitive method which restricts the fishing to shallow water, the fishing here being in water not deeper than thirty feet, but usually three to twenty feet. The sponges are "killed" by being exposed on the beach for several days; they are then placed in "crawls," or pens, where they are washed by the action of the waves for about a week; then, if clean, they are dried, assorted, strung on cords, pressed and baled for shipment. The sponge-fisheries are of considerable value, and much attention is being given to the subject of artificial propagation. It is thought that such beds could be subjected to the regulations which govern oyster-beds. Already the planting of sponges has been shown to be practicable. The living sponge is cut to pieces, and the cuttings are placed in favorable localities. Pieces planted in Florida waters attain a marketable size in one year.

Sponges reproduce by eggs formed in the mesoderm. The eggs escape as ciliated spheres and swim about until they find a place on which to attach themselves. As soon as they become fixed they grow with much rapidity into mature individuals.

Some species seem to prefer association with other animals and live as commensals with crabs. The crab Dromia is always concealed under a sponge, which grows upon its back. Spider-crabs are often overgrown with sponges as well as seaweeds. In this case, however, the crab finds and plants the sponge himself. Aplysella violacea overgrows worm-tubes. Many sponges afford shelter to numerous small animals which bore into their bodies for protection, no animal seeming to feed upon the sponge.

Sponges may be found in tide-pools, on the under side of stones, on seaweeds, and so on. A small bright-red incrusting sponge with irregular lobe-like branches is common on the New England coast; a thin yellow incrusting sponge also is found on the under side of stones. Grantia ciliata, a small urn-shaped species, having a large aperture at the summit, is found in tide-pools.

Perhaps the most singular in habit of any sponge is Cliona sulphurea, the boring-sponge, a common species found from Cape Cod to South Carolina and abundant in Long Island Sound. It [pg106] is bright sulphur-yellow in color, grows in irregular masses of considerable size and fine texture, and has low wart-like prominences. It lives on shells spreading over both surfaces, at first forming little burrows, but eventually penetrating the shell in every direction, honeycombing and at last completely destroying it by absorption. Sometimes it settles upon living shells and greatly irritates the animal, which constantly secretes new lime to cover the perforations in its shell.

These sponges are an important factor in the economy of the sea, as they disintegrate dead shells, which would otherwise accumulate in vast quantities.

SUBCLASS CALCAREA

SUBCLASS NON-CALCAREA

Irregular, uneven, pale-yellow masses spreading over seaweeds; oscula scattered irregularly over the surface; texture close.

PLATE XXXVIII.
Halichondria panicea.	Suberites compacta.
Hircinia campana.	Esperiopsis quatsinoensis (found on the sea-beaches of Alaska).

PLATE XXXIX.
Microciona prolifera.	Chalinopsilla arbuscula.
Chalinopsilla imitans.	Euspongia officinalis, var. tuba.	Chalinopsilla oculata.

PLATE XL.
Euspongia officinalis, var. adriatica.		Hippospongia equina, var. meandriformis.
Hippospongia canaliculata, var. gossypina.	Euspongia officinalis.	Hippospongia equina, var. elastica.

CŒLENTERATA

The animals included in the phylum Cœlenterata were once all called zoöphytes, or animal plants, because of their resemblance to vegetable forms. The name Cœlenterata is derived from two Greek words meaning "hollow" and "intestine," and it describes the anatomical structure of each member of the group. They are commonly known as polyps. In the simplest forms the parts which perform the different functions cannot be distinguished one from the other, and even in higher forms there is but little differentiation. Shakspere's description of old age applies to them: "Sans teeth, sans eyes, sans taste, sans everything."

Nevertheless, this very low order of animals has, like the higher orders, such a diversity of form and habit as to require classification. Some of them are stationary, and of these some branch like plants; some move about by the aid of tentacles, some move by means of vibrating cilia, and others move by the contraction and expansion of the soft body.

Cuvier included them in his Radiata, a class comprising all the animals whose parts diverge or radiate from a central axis. Recent classification has divided the radiate animals into several classes. This arrangement of parts is obviously quite different from that of bilateral symmetry, or the disposal of parts on each side of a longitudinal axis. The type of radiate structure is shown in polyps. The body is a sac, in the center of which is another sac or axis. This is the digestive cavity. Vertical partitions extend from the central to the outer sac, forming distinct [pg114] divisions or chambers. The number of divisions varies with the different species and also with the age of the animal. Other partitions start from the outer sac, and extend toward the central axis, but do not unite with it. These partitions, called mesenteries, are always in definite multiples, varying in different species, new divisions growing between the first partitions in regular order. On the inner edge of these partitions the eggs of the animal are formed, which, when mature, drop into the chambers and pass through openings into the inner sac, or digestive cavity, and out of the mouth into the water.

The animals are classed according as the eggs are formed on all or on special partitions, those being of the highest order where a limitation and constancy of function is maintained. The upper surface of the body has hollow tentacles, each one of which opens into one of the chambers and extends outward. All parts of the animal communicate, and whatever enters the mouth circulates through the whole structure; and when assimilation is completed the residue returns by the same road and is expelled through the mouth. This structure is common to all polyps; but there are great differences in their texture, some being soft and some horny, while others deposit a calcareous skeleton (corals). Some grow in colonies, like the hydroids and corals, and are stationary, others are free and independent; some have but few, others have many tentacles; and they differ widely in size, form, and color.

Hydroids, sea-anemones, corals, sea-fans, starfishes, and sea-urchins are different examples of the radiate structure. They are not, however, all of them polyps.

TERMS USED IN DESCRIBING HYDROIDS

Cœnosarc ("common flesh"): The fleshy axis, or organized living bond, by which the zoöids are organically united to one another. It consists of three layers: ectoderm, endoderm, and mesoderm.

Ectoderm ("outside skin"): The outside one of the three organized layers of which every hydroid is composed.

Gonangium ("seed-vessel"): The external horny receptacle within which the gonophores are developed.

Hydrorhiza ("water-root"): The part of the colony which fixes it to other bodies, like a root.

Hydrotheca ("water-receptacle"): The cup-like, horny receptacle which protects the hydranth.

Mesoderm ("middle skin"): A layer which lies between the ectoderm and the endoderm.

Nematophore ("thread-bearing"): The name of peculiar bodies developed in certain genera from definite points; characteristic of plumularians.

Perisarc ("around flesh"): The transparent, chitinous shell, or unorganized outer membrane of horny consistency, which covers to a greater or less extent the soft parts of the colony.

CLASS HYDROZOA SEAWEED-LIKE ZOÖPHYTES AND SMALL JELLYFISHES

The hydroids have been called the nurses of jellyfishes. From casual observation these two forms would not be associated together, for the shrub-like organisms, which so much resemble plants that they are often collected and preserved as seaweeds, suggest only vegetable life. Examined with a glass, however, they disclose their animal nature. Along the stems, arranged in various ways, are small cups, from which protrude the numerous moving tentacles of the little polyps living within them.

Hydroids are colonies of associated animals living a communal life. The multitude of individuals composing the colony are invested with a horny covering, the perisarc, which in some genera assumes a tree-like form. Through these stems and branches runs a fleshy tube, a thread of animal substance, which connects in one living whole the zoöids, or individuals of the community. There is division of labor, as in other communities: some of the zoöids obtain the food for the colony, and have tentacles around their open mouths; others have no mouths, but reproduce the species, and at certain stages of development liberate swimming-bells, or small jellyfishes (medusæ).

The typical hydroid colony is attached by a kind of creeping stem from which arises a vertical axis, which gives off short lateral, alternate branches bearing zoöids at their ends. There is often more complex branching. The zoöids in certain genera (tubularians) are uncovered; in others (sertularians) they are incased in a glassy, cup-like, horny sheath.

Three kinds of zoöids, polyps, or hydranths—as they are indiscriminately called—are attached to the stem. Those having an [pg120] open end and a crown of tentacles are the nutritive individuals. Small, club-like dilations are immature zoöids. The blastostyles, or reproductive zoöids, are long, cylindrical, mouthless, and covered. At maturity the cover is ruptured, and the medusæ have the appearance of a pile of thin saucers attached by the middle of the convex side. When at length these saucers are set free as little medusæ, or jellyfishes, the convex side of each saucer, or swimming-bell, is called the ex-umbrella; the concave, under side, the subumbrella. From the center of the subumbrella projects the manubrium, or stomach of the animal. At the free end of the manubrium is a four-cornered mouth. From the attached end of the manubrium four tubes or canals diverge, and, extending through the animal, open into a circular canal which runs around the margin of the umbrella. When the medusa is as above described, it has reached the highest point in its development.

When the medusa has matured, it lays eggs, known as planulæ. These are spherical bodies covered with cilia (hairs), by means of which they swim about for a time; but they finally attach themselves to some object, there to grow and develop into hydroid colonies. The cycle of life is thus completed. This process is known as alternation of generation, or metagenesis, one life-history containing two quite different forms of being. The term of life of an individual is one year, the zoöphyte stage beginning in the autumn and the medusa stage in the spring.

Some medusæ, besides reproducing by means of eggs, multiply by budding, small medusæ growing on the manubrium or on the margin of the umbrella. Sarsia and Lizzia sometimes increase by budding.

The Hydrozoa are not all of the above type. In the sertularians the zoöids perish on the stem and have no medusa life, their reproductive element giving rise to the hydroid form without metamorphosis. The Trachylinæ have no hydroid life, being always free-swimming medusæ; others, the Siphonophora, live a hydroid life which is unattached, the colony floating on the ocean; the millepores secrete calcareous skeletons and always remain fixed, reproducing by budding. [pg121]

Hydroids are very abundant, but are comprised in the few groups mentioned: namely, those which live only in the fixed colonial state; those which have alternation of generation, being first hydroids and then swimming-bells, or medusæ; those which live always in the medusa state, the eggs of the jellyfish developing at once into other medusæ; and the Siphonophora, or those which have a floating colonial state, the hydroid never being attached, but floating at large and capable of locomotion, some of the colony having the function of propulsion.

Hydroids are particularly interesting as exemplifying the close resemblance that may exist in outward appearance between animal and vegetable life and as illustrations of communal life and of the alternation of generation. A few examples of different types are given below.

ORDER LEPTOLINIÆ

The members of this order agree in all essential particulars being branched colonies having two principal forms of zoöids, the nutritive and the reproductive. Some genera attain the length of several inches, or even feet; others are very small tufts growing on shells and seaweeds. The cup may completely inclose the zoöid and be close to the stem (sessile), as in sertularians; it may be on the end of a short stalk, as in campanularians; or it may not reach above the base of the zoöid, as in tubularians. The genera are based upon these differences in the perisarc.

The hydroids, like all other classes, exist in such great variety that it would be impracticable to describe here the many named species; but to recognize the genera is simple. A long tubular pedicel without a cup is characteristic of the tubularians; the campanularians have an arborescent form and bell-shaped cups on stalks; the sertularians have sessile cups; and the plumularians have a feather-like form, with zoöid-cups on one side only of the branches.

The beautiful and varied structure of these "animal plants" is most interesting, and to be fully appreciated they should be seen [pg122] in life and examined with a glass. Some species are confined to deep water, but many are littoral and to be found in tide-pools, in the chinks and crannies of rocks, under stones, and under the hanging Fucus. The horny skeletons of large varieties are frequently washed ashore, and in their tangled masses smaller living species often may be found.

THE TUBULARIANS

This division is characterized by zoöids borne on long, slender stems which are sometimes simple and small, sometimes branching and eight to ten inches long. The zoöid has two rows of tentacles, the central one being sometimes on a kind of proboscis. The reproductive zoöids are in bunches, sometimes below the outer row of tentacles, sometimes between the two rows. The perisarc does not cover the zoöid. In color they are commonly red or yellow.

THE CAMPANULARIANS

The hydroids which have an open, bell-shaped cup at the termination of a short, stalk-like stem, or branchlet, are mostly campanularians. This division embraces jellyfishes of different families. Many medusæ cannot be referred with certainty to the hydroids from which they sprang, and the medusa-buds of many of the hydroids have not been noted.

THE SERTULARIANS

The sertularians are distinguished by the horny cup, which is sessile—that is, set directly against the stem instead of being raised upon a stalk. They are among the most common objects of the beach, and, like the plumularians, are often mistaken for plants by the amateur collector and are gathered and pressed as seaweeds. They are found everywhere along the coast. They zigzag over the fronds of seaweeds or hang in fringes upon them, as well as upon rocks, stones, and shells. They well repay close examination with a glass. Every open cup bears a wreath of tentacles, which makes the branch a spray of stars. This is not an inappropriate comparison, for besides their starry shape some species emit a phosphorescent light.

THE PLUMULARIANS

PLATE XLI.
Clava leptostyla.	Coryne mirabilis.
Tubularia indivisa.	Eudendrium ramosum.
Hybocodon prolifer.	Tubularia Couthouyi.

PLATE XLII.
Corymorpha pendula.
Clytia bicophora.

PLATE XLII, A.
Obelia longissima.
Clytia poterium.	Sertularia pumila.

PLATE XLII, B.
Sertularia argentea.	Sertularia cupressina.

PLATE XLIII.
Plumularian hydroid.	Aglaophemia struthioides.
Aglaophemia struthioides, magnified.	Plumularia falcata.

These hydroids are feather-like in the manner of branching, short lateral branches being arranged on each side of a long central stem. In some species the stems are naked below and resemble quills. The zoöid-cups are only on one side of the short branches. (Plate XLIII.)

Family GERYONOPSIDÆ

Family ÆQUOREIDÆ

ORDER TRACHYLINÆ

The Trachymedusæ are characterized by their direct development, the egg of the jellyfish producing a medusa and not a hydroid colony.

ORDER HYDROCORALLINA CALCAREOUS HYDROIDS

The genus Millepora ("thousand pores"), which is the type of this order, is a colony of animals, like other hydroids, which secrete calcareous instead of horny coverings. It differs from true corals in that the members of a colony perform different functions, whereas in true corals each member of a community is a complete individual. It differs also in the arrangement of the stony partitions, which in Hydrocorallina are the outside coverings and connecting canals, but in true corals are vertical partitions inside the animal, between the inner and outer sacs, as explained on page 114.

ORDER SIPHONOPHORA FREE-SWIMMING COLONIES

This order of hydroids consists of free-floating communities and is one of peculiar interest, since it shows in a clear manner the special function of each individual member of the colony, and illustrates better than the foregoing, perhaps, the curious forms of animal life which this class presents.

CLASS SCYPHOZOA THE LARGE JELLYFISHES

There is perhaps no marine animal which excites more wonder than the jellyfish. Its transparency, its graceful rhythmical movements, its long streaming tentacles, the variety and eccentricity of its form, and often of its color, attract attention, and one naturally desires to know something of its life-history. Jellyfishes are also called medusæ, because their long appendages suggest the locks of the Gorgon; acalephs, on account of their stinging or nettle-like properties; and sun-jellies, sea-blubbers, etc., because they float upon the surface during the warmest part of the day, when the sun is high. The name jellyfish is inappropriate, since the animal in no way resembles a fish except in the fact that it swims; but it is, nevertheless, the commonest name.

Jellyfishes vary in size from that of a pinhead to six or seven feet in diameter. They differ in the number, size, and position of the tentacles, the number of the radial canals, the form of the manubrium, the position of the egg-sacs, etc.; but the general plan of the internal structure is the same in all species. In shape they are compared to a mushroom. From the center of an umbrella-like top falls a central organ like the stalk of a mushroom. It is called the manubrium and is the mouth and stomach of the animal.

From the top of the manubrium radiate straight or branched tubes, which are connected with a canal which runs around the whole margin of the umbrella. Extending around the inner circumference of the disk in certain species (usually the hydroid medusæ), there is a horizontal shelf, called the velum, or veil, because it sometimes falls like a veil. [pg135]

From the margin of the umbrella depend the tentacles. There are little mineral deposits, like crystals, called lithocysts, disposed at intervals on the margin, and known also as marginal bodies, which are supposed to be eyes. In some species these lithocysts are inclosed in club-shaped bodies, and they are then called tentaculocysts, because they are like small tentacles. These, together with the nerve-fibers, are called the sense-organs; but to what extent jellyfishes can see and feel is undetermined. This is the first appearance of sense-organs in animals. Around the concave surface of the umbrella is a muscular zone, or zone of contractile tissue, by which the animal opens and shuts the umbrella and gets its locomotive power. The gonads, which are conspicuous from being more opaque than the rest of the body, are the egg- or sperm-sacs. They vary in form and in position.

The jellyfish is carnivorous, feeding on small organisms such as crustaceans and even fishes. The tentacles are invested with stinging-cells, as are also the frills about the mouth, when such occur. With these stinging-cells, which are in some species so powerful as to have been compared with an electric battery, the jellyfish benumbs its prey. The stinging properties are due to nettle-like threads contained in poison-cells. When these penetrate the flesh they produce a pain similar to that of an electric shock.

The food is taken into the manubrium by the square mouth at its free end, and is there digested. It is then sent as nutritive fluid through the canal system of the body, and ejected through small pores in the canal which surrounds the margin of the umbrella.

There are two sexes. The gonads of the female contain eggs; those of the male, sperms. The contents of the gonads drop into the central cavity and pass out through the mouth. The fertilized ovum is called a planula, and is a transparent sphere covered with cilia, by means of which it swims about for a time. At length it attaches itself to some object, and becomes in some species a branching colony (hydroid), in other species a strobila. The latter, as it grows, is constricted at intervals, and at maturity resembles a pile of inverted saucers with lobed edges. Each of [pg136] these saucers is finally detached, and when liberated is called an ephyrula, and becomes a jellyfish. Thus its cycle of life is complete. There are some species which, having no hydroid or strobila state, mature without alternation of generation (metagenesis).

The term of life of the jellyfish does not exceed one year. Even the giant Cyanea attains its immense growth in six months. It starts in the spring as an ephyrula, not more than one half of an inch in diameter, and when it dies in the autumn is often six to eight feet in diameter. The bodies of jellyfishes are ninety-nine per cent. water, and the dead ones thrown upon the beaches by the autumn storms rapidly disappear, leaving no traces behind.

The powerful stinging-cells with which the large medusæ are armed make them formidable enemies, and it is probable that some deaths by drowning are caused by swimmers encountering them and becoming paralyzed by them.

ORDER STAUROMEDUSÆ ("Cross-medusæ")

ORDER PEROMEDUSÆ ("Maimed medusæ")

ORDER CUBOMEDUSÆ ("Cube-medusæ")

ORDER DISCOMEDUSÆ ("Disk-medusæ")

Suborder SEMOSTOMÆ

Suborder RHIZOSTOMÆ

The Rhizostomæ, or root-mouth jellyfishes, are very remarkable. They have no tentacles, but covering the end of the manubrium and hanging from it like tentacles are oval appendages with numerous minute funnel-like apertures, called suctorial mouths. As the manner of locomotion of jellyfishes is peculiar to themselves, so also is this many-mouthed development unique in the animal kingdom. The type of this group, described below, is found on the Florida Keys. The different species vary in diameter from three to eight inches. [pg140]

CLASS ACTINOZOA SEA-ANEMONES, REEF-CORALS, SEA-FANS, SEA-WHIPS, AND SEA-PENS

The animals of this class are divided into two subclasses, based on the following anatomical differences: In the first subdivision, which includes the sea-anemones and the reef-building corals, the polyps have numerous simple, hollow tentacles and radial partitions of the same number, both being some multiple of six. The polyps of a colony are all alike, and the hard matter they secrete is carbonate of lime. In the second subdivision, the Alcyonaria,—or halcyonoids, as they are commonly called,—the tentacles and radial partitions are always eight in number, and the tentacles have small symmetrical appendages or branches. The polyps of this group are often accompanied by small zoöids having no tentacles. The hard secretions are horny and elastic, as in sea-fans, sea-whips, and sea-pens, or they are extremely hard, as in Corallina rubrum.

SUBCLASS ZOANTHARIA ("Animal-flowers")

ORDER ACTINIARIA SEA-ANEMONES

These curious and, at times, beautiful creatures are polyps, and are constructed on the radial system. They have a cylindrical body with a broad base and rows of hollow tentacles around the upper disk. They have a central sac, and a space between the outer and inner sacs which is divided vertically by walls called mesenteries, as explained on page 114. Each tentacle, however many there [pg143] may be, has a corresponding chamber. The inner sac has a mouth, like a slit, at the top of the disk, opening to the outside, and it also has openings into the chambered spaces which surround it. These chambers also open into the hollow tentacles; thus a continuous circulation throughout the whole animal is established.

The food taken in at the mouth is digested in the inner sac, passes through all the chambers of the cavity as nutritive fluid, and is then expelled at the mouth again. The inner sac, or gullet, has longitudinal grooves; two of these are broad and deep, and correspond to the corners of the mouth. These are called siphonoglyphs. The sea-anemone is soft and contractile, and belongs to the only order of this class which does not secrete a skeleton. It has two sets of muscles, one of which extends from the base to the summit of the body and is placed on the dividing partitions. Sea-anemones are classified by the arrangement of the septa and the manner in which the muscles are placed upon them. The other set of muscles is arranged around the circumference of the column or body. Each tentacle is furnished with similar sets of muscles. The animal is sensitive, and at the least alarm contracts its body by means of these muscles, and quickly transforms itself from a beautiful, flower-like form into a shapeless, unattractive, inconspicuous mass.

The Actiniaria are developed from the egg. The eggs form on the edges of the inner walls (mesenteries), and when mature drop into the outer sac (gullet), and out of the mouth as ciliated spheres (planulæ). After swimming about for a time these attach themselves to rocks, and, conforming to the irregularities of the surface, secure a tight hold. The upper surface of the planula then becomes depressed and forms a gullet, and in time a complete animal is formed. The Actiniaria reproduce also by budding. A small protuberance or simple elevation of the body-wall appears on the side at the base, or in some species on the disk of the animal, which generally develops into a complete animal and at maturity falls away from the parent. Sometimes several anemones bud simultaneously from the same individual, and a third generation commences to bud at the same time from the immature young of the parent stock. The sea-anemones increase [pg144] also by self-division. In this case a constriction is formed, which gradually deepens and forms a complete partition of the body, and two individuals exist where originally there was but one.

The Actiniaria are carnivorous and very voracious. They feed on small organisms and on shell-fish and crustaceans, which they suck out of their shells. To secure their prey they are armed with an abundant supply of stinging-cells on the tentacles, and also with fine stinging-threads which are ejected from pores which are distributed over the whole body.

Sea-anemones vary greatly in color and form, and when expanded suggest flowers, but do not resemble the one for which they are named. They abound on every shore, the same genus often being found in widely separated regions. They are larger and more highly colored in tropical waters. Many of the species are littoral, and are found in the tide-pools of rocky caverns, on the under side of rocks, and on the piles of wharves and bridges at low-water mark. The majority of them are attached, but are able to change their location; others, Edwardsia and Cerianthus, swim about when young, and in the adult state burrow in the sand or mud, leaving only their tentacles exposed. Bucidium parasiticum is parasitic on the folds of the membrane which hangs from the mouth of the large jellyfish Cyanea arctica. Fenja and Peachia lie on the sea-bottom, with their bodies horizontal like a worm, the mouth-end and tentacles erect.

Adamsia palliata furnishes another example of commensalism; it lives on the back of shells, commonly the whelk, inhabited by hermit-crabs. Minyas is pelagic; it has a float at one end, and by means of its tentacles swims about freely.

A very few species only are described below, since these polyps are unmistakable, being always columnar bodies, with the upper disk more or less crowded with tentacles, and so brilliant in coloring and beautiful in form as to attract attention if found in the expanded state; otherwise they are easily overlooked.

ORDER MADREPORARIA STONE- OR REEF-CORALS

The coral resembles the sea-anemone and is a polyp constructed on the radial plan (page 113). It lives in colonies, but, unlike the hydroid colonies, each polyp of the community is a complete organism, and in the reef-building corals all the individual polyps of a colony are alike. The home of each animal is called a corallite, and the aggregation of many corallites is a corallum.

The corallite is composed of carbonate of lime secreted by the polyp, and, broadly speaking, may be called a skeleton. The secretion forms a basal plate and radiating partitions between the mesenteries in the cavity of the animal, and also surrounds the polyp like a cup. In some species this is a solid substance; in others it is like a network through which the animal substance (cœnosarc) of the zoöids of the colony is connected, as in Madrepora.

The polyps reproduce by budding and by self-division (fission), in a manner similar to that of sea-anemones. The way in which the budding or the fission takes place determines the shape of the colony, or corallum, which has a great variety of forms. In some species the budding is confined to certain individuals of the colony. In this case the branched forms result. When growth takes place by fission, hemispherical masses are formed, which are often perfectly symmetrical, as in the so-called brain-corals. In Astræa the polyps are inclosed separately, but in Meandrina fission is confined to the upper half of the polyps, so that a complex polyp is formed, with several mouths opening into a common stomach, making long serpentine furrows on the corallum.

Some of the genera of the second subdivision, the alcyonarians, differ materially from the ordinary idea of corals, as their framework is of a horny and more or less flexible material (chitin). Of these are the sea-fans, sea-whips, and sea-pens. The organ-pipe coral of the same subdivision is an example of an exceedingly fragile lime structure, while the red coral, Corallina rubrum, [pg147] the species so much used for ornamental purposes, has an exceedingly hard and stony character. The madrepore corals are called reef-builders, but not in the sense of constructors of reefs. They do not erect definite structures as bees do. It is the aggregation of the skeletons of the dead polyps, together with other agencies, which forms a reef. The coral polyps, though so minute individually, are almost infinite in numbers. It is estimated that the colonies rise one half of an inch in ten years.

Corals live at different depths in the sea. Those which form the base of the reef are the astræans, which do not live above a depth of six fathoms. They are characterized by little star-shaped spots on the corallum, the radial partitions meeting in the center of the spots, or corallites. Next above the astræans come the mæandrinas and the porites. The former have elongated openings which extend in waving furrows over the surface. The porites resemble astræans, but the pits are smaller, with fewer partitions, and the substance is more porous. Above these and capping the reefs are the beautiful branching and palmate madreporians, together with millepores, numerous varieties of sea-fans (Gorgonacea), and the calcareous seaweeds (nullipores), making a garden of beautiful branching forms of every shape and color.

The coral reef is as thickly inhabited by other living organisms as is the forest by birds and insects. Mollusks, worms, crabs, starfishes, and sea-urchins find resting-places there and work destruction to the coral masses, as they bore and penetrate the reef in various ways until large fragments of it are detached and either washed by the waves to places far from their foundation, or ground to sand, which, filling the interstices of the reef, adds to its solidity.

The living coral is quite different in appearance from the bleached skeletons commonly seen. The surface of the corallum is often soft and downy, from the numerous waving tentacles, and its coloring is vivid and varied. The madrepores are pink, yellow, green, brown, and purple. Tubipora, the organ-pipe coral, has green polyps emanating from its red tubes. White polyps in star-like form dot the branches of the red coral of commerce, Corallina rubrum. The whole mass of Helipora is bright blue, [pg148] and the beautiful sea-pens are both highly colored and phosphorescent. Owing to the fact that these brilliantly colored polyps were mistaken for blossoms, the recognition of their true character was long delayed, they having been ranked as vegetables until comparatively recent times.

With few exceptions, corals do not grow in water below the temperature of 68°, hence they are inhabitants of tropical and subtropical waters. The Florida Keys are coral reefs, and the species described below are to be found there.

Arborescent; corallites arranged somewhat spirally on branches and widely separated; branches compact between corallites. Each bud is for a time at the apex of the branch, but finally becomes lateral, and then gives off another bud from its upper surface, and so the stem lengthens. (Plate XLIV.)

The star-corals. The corals of this genus are hemispherical masses covered with small star-shaped pits, or corallites. Although the diameter of an astræa-dome may be twelve feet or more, it has only one half or three quarters of an inch of living coral on its surface, the rest being solid matter left behind as the polyps rose in growth. The colony increases by self-division. The septa meet in the center of the corallite, making star-like pits; the surface is comparatively smooth. (Plate XLIV.)

Corallum massive, hemispherical in shape, with furrows running in irregular lines over the whole surface. The peculiar serpentine form of the corallite is produced by the animal growing in one direction, fission being incomplete, and new mouths being successively opened until a line of them extends along a common stomach.

Some species of these corals appear like branches, while others have flat, low surfaces or fronds; all of them are covered with innumerable small cylindrical cups. Each cup is the home of a polyp, which secretes calcareous matter around its column, and septa between its radial partitions. The corallum, when examined with a glass, looks like meshwork. Through the fine openings of the porous surface, the polyps of the colony are connected by interlacing tubes of animal substance (cœnosarc). The polyps of the madrepore colonies are small in comparison with the connecting structure, which becomes very massive; but, although large, the corallum is fragile, on account of its perforated character and the exceeding delicacy of its parts.

In species which form incrustations, new polyps arise from tissue which spreads beyond the corallites. In some species certain polyps and corallites increase in length, growing longitudinally, and continually form buds around the base. This manner of growth leads to the formation of branches, while the former manner gives lateral extension. Both of these forms of budding may take place at the same time in the same colony. The madrepores are among the most common of the reef-builders. They form reefs which extend for miles around the Florida Keys.

PLATE XLIV.
Millepora alcicornis.	Lucernaria auricula.
Cassiopeia frondosa.	Astræa argus.
Oculina.

PLATE XLV.
Porites furcata and P. astræaoides.	Diplora cerebriformis.
Madrepora cervicornis.	Madrepora palmata.
Mycedium fragile.

SUBCLASS ALCYONARIA or HALCYONOIDA

In this subclass—the actinoid corals—the polyps are of two kinds. The smaller are without tentacles and are called siphonozoöids. The larger have but eight radial partitions and eight tentacles. This limitation of parts places them in a higher rank than the corals of the first subclass. Another characteristic of these polyps is the presence of symmetrical branchlets on the tentacles, which give them a feather-like appearance. These corals are called halcyonoids. [pg151]

Some of them may easily be fancied to have been selected for halcyons' nests, as the name suggests—the sea-fans, for example.

ORDER ALCYONACEA

The organ-pipe coral. This genus, which is deep red in color and very fragile, consists of many tubes slightly separated from [pg152] one another, but connected by horizontal platforms at short intervals. The form of reproduction, by budding, in this colony is peculiar to itself. The spicules of lime secreted in the polyp unite or fuse into a tube or cylindrical skeleton. At certain stages of development the polyp sends out a horizontal expansion, which unites with the expansions of other polyps and becomes calcified, forming a shelf which binds the tubes together. From the top of the platforms other corallites are formed, and thus a colony is made, which broadens as it rises in its growth. The body of the polyp is green, the skeleton red. It belongs to the East Indian seas and is given here only as an example of a peculiar manner of growth.

ORDER GORGONACEA SEA-FANS, SEA-WHIPS, AND SEA-FEATHERS

These are compound, tree-like Alcyonaria, with a calcareous or horny skeleton which forms a branched axis and is covered with a layer of united polyps having spicules of lime distributed through the mass, which give some firmness to the bark-like covering. Gorgonias, in great variety, grow in abundance on the coral reefs and mud-flats of Florida, forming masses of low shrubbery, pink, yellow, brown, or purple in color.

The sea-whips and sea-feathers are varieties of gorgonias, which are named from their forms. Some have shapes which resemble branching shrubs; others are long unbranched rods, either straight or spiral. They attain a height of several feet and are of various colors. The colony has a horny axis surrounded by a living mass which resembles a sheet of animal matter. This mass consists of polyps closely united, and has throughout its substance spicules of carbonate of lime, making it a kind of calcareous crust or bark. In dried specimens this becomes very brittle, and is easily broken from the horny axis. (Plates XLVI, XLVII.)

The sea-fans are colonies with a central, horny, flexible, and much-branched axis, covered, as in the sea-whips, with a layer of united polyps containing spicules of lime, which make a somewhat [pg153] firm crust. This, in dried specimens, breaks off readily. The colony branches profusely, or rather separates by fission, in one plane, the large and small branches making a network of fan-like shape and often of great fineness and intricacy. These fans attain a length of several feet and a corresponding breadth, and are abundant in semi-tropical as well as in more southern waters. In color they are red, yellow, brown, or purple.

ORDER PENNATULACEA SEA-PENS

These singular colonies resemble quill-feathers, such as are used for pens, and are named for this reason. The long, horny central axis is naked below, and is partly buried in the sand, but is not permanently attached. The upper portion of the axis has two rows of short, opposite, lateral branches; on the upper side of the branches the polyps live in separate inclosures. Spicules of lime are present in the substance of the branches, which gives them stability. Sea-pens are found at moderate depths and are widely distributed. They are highly colored and phosphorescent. [pg154]

CLASS CTENOPHORA COMB-JELLIES

These are delicate, free-swimming, generally spherical bodies, resembling jellyfishes in outline, transparency, and gelatinous consistency, but differing from them widely in the manner of locomotion. They are called "comb-jellies" from the rows of flat cilia, arranged like the teeth of a comb, which run in eight meridional lines over the surface. It is by means of these cilia that the animal moves through the water. The little paddles are worked in unison, in single lines, or each one of them can be moved independently, and they give the animal varying and peculiar motions. The Ctenophora are nearly transparent, but have a prismatic coloring, caused by the waving cilia, and at night they are phosphorescent. They are widely distributed, being found in all seas.

The mouth of the animal opens into a gullet which extends two thirds through the length of the body. On each side of the gullet is a vertical tube. The two tubes unite at the base of the gullet, and from there run as a single canal to the end opposite the mouth, and open to the outside through two excretory pores. From the base of the gullet, where the tubes unite, two other tubes extend laterally, which divide and subdivide in a horizontal plane, becoming eight in number, and connect at the surface with the lines of cilia; then, dividing, run in opposite directions to the poles of the spherical body. The animal derives its nourishment and air through this circulatory system. A nervous system is situated at the pole opposite the mouth, in a small area surrounded by cilia, in the center is an eye-speck, or lithocyst. [pg156]

ORDER CYDIPPIDA

ORDER LOBATA

ORDER CESTIDA

ORDER BEROÏDA

WORMS

Burrowing in sand and mud, lying under stones and in crevices of rocks, concealed in various kinds of tubular cases which are free or attached to stones or shells, crawling over the ground or seaweeds, swimming free or attached to other animals, is found in abundance a class of animals commonly known as "worms," and generally regarded as repulsive creatures unworthy of attention.

To the biologist, however, worms are among the most interesting forms of lower animal life. The amateur collector, if he stops to give them careful consideration, will probably find them unexpectedly interesting, and will be surprised to find how many varieties of them there are, and how different they are from his preconceived notion of them. Worms are varied in structure, their habits are strange, and their form and color often beautiful. Although plentiful, they are not conspicuous, but are easily found if search is made for them, and so large a class of shore animals should not be passed by unnoticed. Unusual biological interest is attached to this group because, in the different types, affinities with other classes of animals are found, suggesting, perhaps, connecting-links with higher organizations. They are the first animals to show definite bilateral symmetry, or two similar sides, and to carry the same part of the body always in front. Formerly one division, called Vermes, comprised all the worms. To-day they are separated into four divisions, or phyla. The most careless observer easily recognizes the basis of separation, for the flatworms, the round- or threadworms, the wheel-like animalcules, and the jointed worms have very obvious differences. The names given the phyla express these distinctions, the termination [pg164] meaning "worm"; the prefixes Platy-, Nemat-, Troc-, meaning "flat," "thread," "wheel," respectively; while Annulata, meaning "ringed," describes the segmented forms belonging to that phylum.

There are vast numbers of parasitic worms, which live internally or externally on their hosts, there being no animal of land or sea, of high or low degree, which is not subject to the affliction of these visitors. The parasitic worms are degenerate, some being without digestive organs, or without eyes, or without locomotor organs, and so on, as the case may be, the host supplying the missing function. The life-history of these low forms is interesting; but parasitic worms do not come within the scope of this book, and are mentioned only to mark their place in the series.

PHYLUM PLATYHELMINTHES FLATWORMS

The flatworms have a flattened body, more or less compressed in the different classes. Ordinarily the body is very thin, and, when short, has a leaf-like form; when long it is ribbon-like. Some species are thick in the middle and thin at the edges. They have a dorsal, or upper, and a ventral, or under, surface; a right and a left side; an anterior and a posterior end. The anterior end is carried forward and has some of the characteristics of a head, though a distinct head is not apparent. The mouth is on the ventral surface. In some species it is in the middle of the length of the body; in others it is before or behind this point.

The flatworms are the first animals to assume pronounced bilateral symmetry. They are soft-bodied, having no supporting skeleton, and they have no segments, or divisions, such as are found in higher types, as in Annulata. They have no body-cavity, the space between the organs and the body-wall being filled with tissue. The alimentary canal has no anal aperture, the excretions being carried off by a water-vascular system consisting of branching vessels which end in minute bundles of vibrating cilia, called ciliary flames. These flames communicate with the exterior through small pores or flame-cells. Their sense-organs are eyes [pg165] and otocysts. The latter are sacs containing crystals of carbonate of lime, and their function is supposed to be that of hearing.

The flatworms are hermaphroditic, and their propagation is by means of eggs. They are numerous and very generally distributed, occurring in fresh and salt water, on land and shore, on the surface and in the depths of the sea. A vast number also are parasites and infest, internally or externally, nearly every living creature. The parasitic forms differ anatomically from the free-living worms. The internal parasites, living by absorption of the digested food of their hosts, have no digestive organs; they are also devoid of organs of sense and of defense. The external parasites, being carried about by their hosts, are without organs of locomotion.

CLASS TURBELLARIA

The turbellarians are the simplest group of bilateral animals and occupy the lowest place among worms. They owe their name to the fact that they are covered with cilia, which are constantly in motion and cause a slight turbulence in the water around them.

ORDER POLYCLADIDA ("Many-branched")

The polyclads are found below half-tide mark on the under side of stones and on seaweeds. Sometimes they are found swimming about at night. They are leaf-like in form, one inch to two inches in length, and are very thin and delicate. They adapt themselves to the inequalities of the surfaces to which they attach themselves, and often are of the same color, and therefore are so inconspicuous that they are apt to escape notice. They move with a gliding motion over surfaces, and often swim when in search of food.

The intestine is much branched and has no anal aperture. From the mouth, which is placed in the center of the ventral surface, a pharynx, or muscular fold, is protruded in some species, which enables the worm to attach itself to and consume prey of considerable size. After digestion has taken place, the fecal [pg166] matter collects in the main intestine and is forcibly ejected by the pharynx. Numerous eyes are collected in groups on the anterior dorsal surface, or arranged around the margin of the body. The eggs are laid in shell-like cases, and cemented together in plate-like masses or in spirals, and attached to shells or stones. (Plate XLVIII.)

ORDER TRICLADIDA ("Three-branched")

The triclads are divided into three groups: those of the fresh-water ponds and streams, those of the land and sea, known as planarians, and those of the sea. The planarians are the most interesting worms in the order. The triclads differ from the polyclads in being elongate in form and in having the intestine in three branches instead of in many. The mouth is midway in the length of the body, on the ventral side, and from it protrudes a pharynx, which is cylindrical or bell-shaped, and is capable of great dilatation. With the pharynx the worm, which is wholly carnivorous, envelops other worms, crustaceans, or any animal food. Several species are found on the under side of stones in tide-pools.

ORDER RHABDOCŒLIDA

Minute, active worms found among the red seaweeds. They are brown in color, and are marked by one or more transverse white bars.

CLASS NEMERTINEA

The nemerteans are long, narrow, flat, smooth worms, and vary from one half of an inch to many feet in length. They are exceedingly contractile, and when alarmed can shrink to less than half their normal length. They are very generally distributed, and are to be found between tide-marks, in loose coils like a string, under stones on sandy and muddy shores. The very long species, like Lineus marinus, are solitary, but other smaller species are gregarious, many worms being coiled together in tangled masses. Some species are to be found in empty shells, and others live among the seaweeds. They are very slimy, the epidermis secreting an abundance of mucus, and they can often be tracked by the trail of slime they leave behind them. This mucus sometimes hardens, forming for some species a tubular [pg168] covering; others remain naked. All are covered with vibrating cilia, which is a universal feature of flatworms. In color they may be white, yellow, green, red, purple, etc., and sometimes they are banded or striped with a contrasting color. The ventral is usually lighter than the dorsal surface.

The principal characteristic of the nemertean worms is a long thread-like organ, known as the proboscis. This lies in a sheath along the center of the dorsal surface, and is quickly thrown out to a great length, and as quickly completely withdrawn within the body. The proboscis is slender, hollow, muscular, and full of nerves. It reaches the outside through a pore at the anterior end of the body, and has no connection with the alimentary system. It is used as a feeler and as a weapon. Some species have a sharp spine at the end of the proboscis, others have stinging-cells. The proboscis is sometimes so forcibly ejected that it breaks off, in which case it retains its vitality for some time, and seems as if it were itself a worm. A new proboscis is quickly grown by the worm to take the place of a lost one. The head is a little broader than the body, and has eyes arranged in one or several pairs on each side. The mouth is on the ventral surface, near the anterior end, has thick lips, and is very dilatable. Through the mouth the animal ejects a part of the esophagus and envelops its prey, which is often of considerable size. Chætopod worms they often swallow whole; the soft parts, after being digested, are carried off through the regular passages, ending in the ciliary flames (page 164), while the indigestible parts are ejected at the anus. Often the spines and bristles find their way out by perforating the intestine and the body-wall, without apparently doing the worm any injury. The perforated parts quickly heal.

These worms have the strange power of regenerating lost parts; mutilated portions are soon repaired. The anterior end, when severed from the rest of the body, grows again into a complete individual, while the posterior end continues to perform part of its functions and retains its vitality for a considerable time before dying. One species, Lineus sanguineus, is capable, after being broken in pieces, of regenerating each section into a perfect worm. [pg169]

The nemerteans are carnivorous, voracious, and often cannibalistic. They will live for some time in confinement, losing, however, their bright color, and the smaller worms will gradually disappear, as they are devoured by the larger ones. The mode of locomotion varies with the order. Some species attach their long proboscis to a distant object, then drag the body to it; some glide rapidly along by means of the muscles of the body and the cilia which cover it; others swim. The swimming forms have thin edges which have a wave-like motion, and this, together with a lateral movement of the tail, propels them through the water. In some species the worm develops directly from the egg; others pass through a larval stage before reaching maturity.

PHYLUM NEMATHELMINTHES ROUNDWORMS

The worms of this phylum have the general name of roundworms, which distinguishes them from the flatworms of the preceding division and from the segmented worms of the Annulata. The body is elongated, cylindrical, smooth, and pointed at both ends. With few exceptions, they are parasitic.

A few of the nematode species are free, living under stones and among seaweeds at about low-water mark.

CLASS NEMATODA

PHYLUM ANNULATA SEGMENTED WORMS

The name of this phylum expresses the principal characteristic of the group of worms which have elongated bodies composed of series of short parts, or ring-like divisions. Each one of these segments contains a separate and similar set of internal organs. [pg171]

The annelids are divided into four classes, one of which, the Gephyrea, has not the characteristics which distinguish the group. The classes are easily recognized by conspicuous features. Some have bristles; others have scales; others have tentacles around the head and inclose themselves in tubes. Many are highly colored, and all are of great interest to the naturalist from the diversity of their habits, form, and structure, and from the analogies they bear to other and higher types of animals.

The annelids are the highest type of worms, their organs having attained more special functions. The sense-organs of eye and ear are more developed, and the nervous system has distinct centers, or ganglia, the first and largest ganglion being a part of the head. They are found in abundance everywhere. Some species grow to the length of one foot or two feet. Some are carnivorous, others vegetarian, and many are mud-eaters, swallowing sand and mud for the sake of the organisms they contain. They themselves are food for fishes, which devour them in vast quantities, rooting them out of their burrows or capturing them at night, at which time they swim about.

CLASS CHÆTOPODA ("Bristle-footed")

The bristle-worms. This class of worms has bunches of bristles on both sides of each segment of the body, which serve as organs of locomotion, or bristle-feet. The bristles emanate from outgrowths of the body known as parapodia, which are practically limbs. The parapodia are sometimes divided into distinct lobes or branches. The bristles are of various shapes and often of brilliant color. They are usually horny, sometimes simple, sometimes divided into joints, and vary in shape in different genera. The parapodia have, besides the bristles, a second set of [pg172] hair-like appendages, called cirri. These are sense-organs and also have a respiratory function. The cirri too vary in shape in different genera. Generally they are hair-like, but sometimes conical; again they are broadened into scales, as in the Aphroditidæ.

The body-cavity in chætopod worms is divided into a series of chambers or segments. These divisions seem on the exterior like constrictions, and give the body the appearance of a series of rings. The internal organs are repeated in each segment, so that each of the latter contains a portion of the alimentary canal, a pair of nephridia, a pair of nerve-ganglia, and blood-vessels which connect the main blood-vessels running along the dorsal and ventral surfaces. The alimentary canal runs through the body, but is constricted at each joint. The nephridia are curved tubes, which are excretory organs, opening to the outside and carrying off the waste products which have passed into the fluid of the body-cavity.

The chætopod worms have a well-developed nervous system, beginning with a two-lobed ganglion forming a brain and head, then extending through the worm in a double ventral chain and series of ganglia. They have also a blood-vascular system. The blood is either colored or colorless. Sometimes it is a bright red or green, and is often visible through the body-wall. The circulation is effected, not by means of a heart, but by wave-like (peristaltic) contractions of the dorsal blood-vessel. The body is cylindrical, but in many cases is somewhat flattened. There are two layers of muscles, one of which encircles the body, while the other extends parallel with its length. Respiration is effected by gills, which may be simple, hair-like appendages to the parapodia, or branched, or comb-like in form. Sometimes they are confined to the middle segments, as in Arenicola; sometimes to the segments near the head, as in Tubicola; or they may be extended over the whole dorsal surface.

SUBCLASS POLYCHÆTA ("Many-bristled")

The polychæte worms have one or two well-developed parapodia, or limbs, on each side of every segment of the body, and on each [pg173] parapodium is a bunch of bristles, or chætæ. There are hundreds of species of this class of worms, the species being based on the shape and the lobes of the parapodia, the relative length of the cirri, the form and arrangement of the chætæ, and so on. They are abundant on the shore everywhere, but abound where rocks and stones afford them some shelter. Many burrow in the sand and mud. In doing this the worm eats his way into the hole, swallowing the mud and sand. He assimilates the organic or vegetable matter the mud contains, and ejects the rest in cylindrical coils, known as castings, which lie in heaps at the mouth of the burrow. By these castings they may be traced. Others secrete tubes.

The polychæte worms are divided into Errantia, which are wandering, free-swimming forms, and Sedentaria or Tubicola, which live in tubes permanently. These distinctions are not strictly correct, since some species of errant polychætes form tubes (Eunicidæ), and some Sedentaria form no tubes.

Many polychætes are beautifully colored, some in vivid reds and greens, with various markings; some are iridescent; some are phosphorescent.

Carnivorous, free Polychæta, with protrusible pharynx armed with a horny jaw. "They are active, fierce beasts of prey."

This family is the highest in organization of the worms. They are small, the majority being less than an inch in length, and many are minute. They are often highly colored. Many have long cirri on the feet; some have alternation of generation. They are common everywhere along the coast, but are not seen unless searched for. Sponges sometimes are alive with them. They are interesting subjects for microscopic study.

The scale-bearing annelids. This family of worms is distinguished from all others by having scales on the back. The scales, called elytra, are flattened dorsal cirri carried on the upper parapodia, [pg174] and generally on alternate segments and in a double row down the back. The elytra are the breathing-organs, and, although of a horny texture, are richly supplied with nerves. The worms are short and have a large protrusible pharynx armed with a double pair of horny jaws.

The species of Polynoë are determined by the number of scales they bear. They have a flattened short body with nearly parallel sides. The bristles are of a bright golden color. The proboscis is large and has four powerful jaws at the end and a circle of papillæ at the top. They are sluggish in movement and are found under stones and in the crevices of rocks. When disturbed they roll themselves into a ball.

These animals are commonly known as "paddle-worms," on account of having leaf-like cirri, which they use in locomotion. The head is long and bears four pairs of short and four pairs of long tentacles. The body is long and depressed, sometimes two feet in length, usually eight to twelve inches long. The general color is bright green and iridescent. Found in tide-pools. Specimens are often found by digging in sandy mud, or they may be obtained by placing old shells and other material in a dish of sea-water. When the water becomes a little stale, the worms of this and other families make their way to the sides of the dish, where they secrete a colorless slime which holds mud or any light matter that it may come in contact with. In this condition, when lifted or disturbed, they crawl rapidly out of the slime, and show to good advantage their elongate body, which is often beautifully colored.

Among the most common of the polychæte worms is the genus Nereis, various species of which are found in all parts of the world. They are abundant under stones, among seaweeds, and living in burrows between tide-marks. They are active, fierce, and voracious. Some attain a length of eighteen or more inches. They are commonly known as "clam-worms," and are used by fishermen for bait. Nereis has a distinct head, consisting of two parts. One, the prostomium, bears on its upper side four eyes and a pair of short, conical tentacles, and on the lateral sides a second pair of processes called palps. The palps are more conspicuous than the tentacles, and consist of two parts, a large base and a small terminal point, the latter capable of being withdrawn. The palps are sense-organs and perhaps test the food. The second part of the head, or peristomium, bears on the sides four pairs of long tentacles which are used as feelers. The mouth is on the ventral side, and through it Nereis throws out its pharynx, which contains a horny, notched jaw. It seizes its prey with this jaw, which, with the pharynx, is then withdrawn and tears the food apart, acting like a gizzard. The body of Nereis is rounded above and nearly flat below. Each of the segments has a pair of parapodia, bearing a bundle of bristles and cirri. The last segment of the body is elongated, cylindrical, and without parapodia, but has on the end a pair of long cirri, which give the appearance of a divided tail. Each segment of the body, except the head- and tail-segments, contains a pair of excretory tubes (nephridia), ganglia of nerves, and a portion of the intestine and of the vascular system. There are circular muscles by which the worm can diminish its diameter, longitudinal [pg177] muscles in four bands, and muscles to move the parapodia. Breathing is carried on over the whole surface of the body, and especially in parts of the lobes of the parapodia called gills. Its sense-organs are eyes, palps, tentacles, and cirri.

In this family the worms have a long, thick, flattish body, a section of which has a quadrangular form. The lobes of the parapodia are widely separated and fringed [pg178] with membrane, appearing like double parapodia. The pharynx is very large and projected as in Nereis.

These are beautiful worms, having a reddish-brown iridescent body, with bright-red branching gills, which look like feathers, along the back. They form parchment-like tubes.

These worms are long and smooth, with numerous segments. They taper at both ends. The head is small, conical, sharply pointed, and has four very small tentacles. The proboscis, or [pg180] pharynx, when protruded, is very large and long, and appears too large for the worm. The proboscis has four hook-like jaws. These worms burrow rapidly and disappear almost instantly into the mud or sand.

Many of this order construct tubes in which they live permanently. Some species of both Sedentaria and Errantia have habits pertaining to the other. These worms are without a protrusible pharynx and without jaws. The body is usually divided into two or three sections by segments and appendages of different forms. They have hair-setæ on a limited number of segments only, varying with the species; the remaining segments have uncini, or hooked comb-like rows of setæ, which are very small, but often crowded in bunches. Uncini exist also on segments having hair-setæ. Parapodia are often lacking on the posterior parts and are usually without cirri. The gills are usually confined to the anterior end and are sometimes represented by tentacles around the head. The different species have characteristic tubes, formed by mucus secreted by epidermal glands. Sometimes the mucus hardens, making a parchment-like tube; again it cements together grains of sand, or bits of shell, seaweeds, etc. Some species secrete [pg181] calcareous tubes; these are often found on rocks, in coral, and in the shells of mollusks. The anterior end of the body is more highly developed than the posterior end.

Worms of this family have a cylindrical body, more or less attenuated at each end; segments similar throughout; many segments with long, filamentous cirri which act as gills; and a conical head. They live in burrows.

The body is cylindrical and largest on the anterior end; there are one to three pairs of more or less branched gills on the anterior end, and the ventral surface of the anterior segments is thickened by glands which secrete mucus for tube-building. These gland-spaces are called shields.

The tubes of these animals are formed of sand, a short portion projecting, and are very abundant in certain places. There is a horny plate on the upper surface of the head, and the skin on the sides of the head is raised in folds. There is a funnel-like process at the posterior extremity; gills are lacking. Some of the segments in the middle of the body are longer than the rest.

In this family the gills arise from two semicircular bases forming the crown; the second lobe of the anterior extremity is reversed like a collar; the gill-filaments have secondary processes, and the tubes are flexible, composed of cemented mud or sand. Found under stones, the tube passing around the stone and opening upward.

This family forms white calcareous tubes. One of the dorsal gill-filaments is flattened, forming an operculum, or cover, with [pg185] which the tube is closed when the worm has withdrawn itself inside. The tubes are commonly found attached to shells and rocks, usually solitary, but sometimes in clusters, crossing and recrossing each other on the surface of the shell or rock. Plume-like gills are attached to the anterior end of the body. The color differs in different species. These worms may easily be mistaken for the mollusks Vermetus, which live in similar tubes of larger size, growing in masses.

CLASS GEPHYREA

This class of animals, once placed near the holothurians, belongs with the annelid worms on account of their mode of development, their structure being entirely dissimilar. They are without segments and without parapodia. The body-cavity is filled with fluid and is traversed by connective tissue and fine muscular fibers. They are subcylindrical animals which can retract the anterior end of the body. The mouth is surrounded by tentacles, or by tentacular folds, and is at the base of the proboscis. They live in fissures of rocks, in sand, mud, rock, or coral, and in deep gasteropod shells. Their distribution is general.

ORDER SIPUNCULOIDEA

TERMS USED IN DESCRIBING POLYZOA

Avicula´ria: Specifically modified zoœcia, resembling a bird's head, found only in the Cheilostomata.

Brown bodies: Brown pigment-masses contained in the zoœcia and derived from the breaking down of the polypides.

Vibra´cula: A lashing filament, or specifically modified zoœcia, found only in the Cheilostomata.

POLYZOA

Among the numerous objects to be found on the beach at low tide are the Polyzoa, of which there are said to be seventeen hundred named species of the marine forms. These little animals, although so plentiful, are inconspicuous, and it may be said that their very existence is not known to those who are not professed naturalists; yet they are easy to see, incrusting with a delicate calcareous lacework the surface of stones and shells and seaweeds in the tide-pools, and hanging from the rocks like branches of delicate seaweeds. There is hardly a frond of even the fine red algæ on which cannot be found the little tube holding shelly saucers, or the creeping stems or branches of polyzoans. Any one of these little masses, when examined with a pocket-glass, will surprise one with its delicate and beautiful structure.

This class of animals is also called Bryozoa, and certain species have the common names of sea-mats and corallines. They are broadly divided into two groups, namely, the erect and the incrusting forms. Those having tree- or plant-like shapes resemble seaweeds, while the colonies which spread over stones, shells, and algæ resemble moss, hence the name Bryozoa (moss-animals). Both groups have the general appearance of hydroids, because, like them, they are colonies having plant forms and having their organisms inclosed in cup-like sheaths. The resemblance, however, is but a superficial one, for the Polyzoa have a much higher organization, each animal of the colony being a separate and distinct individual. They can easily be distinguished by the hair-like processes on the tentacles. The ciliated tentacles and complete alimentary system are the conspicuous differences between these colonies and those of the hydroids.

The Polyzoa are very numerous and form a most attractive [pg192] group. They are plentiful everywhere, occurring between tide-marks and at great depths on the floor of the sea. Rocks protected from the sun are often incrusted with the calcareous forms, while branching species hang from the rocks and adorn rock pools. Membranipora, in lace-like sheets, will be found on the larger seaweeds as well as on various submerged objects. The beautiful little Crisia may be looked for on the fronds of red algæ, and Alcyonidium, in soft moss-like patches, on Fucus. On some beaches are scattered the sea-mats, Flustra foliacea, looking like bits of brown paper. A pocket-lens will reveal the marvelous and orderly arrangement of the two layers of cells, or zoœcia, placed back to back. There is not a more surprising object in the animal kingdom than a living branch of Bugula. The cells on its spiral, profusely branched clusters have appendages resembling a bird's head, with its bill constantly opening and shutting. Of the erect polyzoans some are entirely calcareous and rigid; such species live in deep water, and their colonies are called corallines, as are also the calcareous algæ. They have existed in vast numbers since early geologic times, and are plentiful in the Tertiary deposits, known as Coralline Crags. Other erect forms have a calcareous framework, which is not continuous, but has horny intervals, so that the colonies are flexible and can be swayed by the tides in shallow water where they live. Others have complete horny exoskeletons. The same differences occur in the incrusting forms, those on the seaweeds being either flexible, so that they bend with the plant, or if entirely calcareous are so small that they do not break when the plant sways to and fro. Still others are gelatinous and resemble bits of sponge. The calcareous forms are usually ornamented with ridges which form beautiful patterns.

The individuals of the polyzoan colonies are small polyp-like organisms which have a cup-like inclosure of horny or of calcareous substance, or of the two combined, as mentioned above. This inclosing sheath is the exterior or cuticle of the animal and is called the zoœcium, the whole colony being called the zoarium. The animal substance within the zoœcium is the polypide, and consists of the mouth, tentacles, and alimentary system. A disk at the anterior end of the body, bearing the circle of tentacles, is [pg193] the lophophore; it is a contractile body, being, with the tentacles, protruded from the zoœcium or drawn within it at will. In some species the orifices of the zoœcia are surrounded with spines; others have lids, called opercula, which shut down when the polypides are retracted. A singular modification of the zoœcia is seen in the genus Bugula, where peculiar shapes like birds' heads, called avicularia, occur. In these singular appendages the upper beak is hooked, while the lower one, or mandible, is the operculum of the zoœcium. These constantly open and shut by means of muscles, and although their function is not certainly known, it is thought that they capture prey. Other modifications are whip-like processes, or flagellate filaments, called vibracula, which constantly beat the water. In many of the zoœcia of the colony there are dark-colored masses, called brown bodies. These are formed by the degeneration of the polypides, which at certain periods break down, their tentacles and alimentary system ceasing to act and becoming brown masses. The body-wall then puts out a bud internally and forms a new polypide, which absorbs, or passes out, the brown body. The term of life of a single polypide is not known, but in every colony many such transformations are constantly taking place.

The colonies originally start from larvæ produced in the ovicells of the zoaria. The ovicells are sometimes very large and pear-shaped, occurring at intervals on the stems; or there may be one at the top of each zoœcium. They look like pearls. A larva, when liberated, swims about for a time, then attaches itself to a fixed object, and increases, by budding, into some one of the various forms which the colonies take.

SUBCLASS ECTOPROCTA

ORDER GYMNOLÆMATA

The zoœcia are more or less cylindrical; the upper ends are sometimes completely free and sometimes closely adherent. The [pg194] opening of the cell has no operculum. Ovicells, containing the embryos, appear like pear-shaped swellings.

In this suborder the zoœcia are either horny or calcareous, and the orifices are usually surrounded with spines and have opercula. The orifices generally have raised margins, or peristomes. Ovicells form helmet-like coverings overhanging the orifices.

SUBCLASS ENTOPROCTA

TERMS USED IN DESCRIBING THE STRUCTURE OF ECHINODERMS

Dorsal surface: The back of the animal, generally, but not necessarily, the upper side.

Exoskeleton: Outside framework or support, differing from a true skeleton which lies inside the body.

Larva: The animal in a stage of development from the time it leaves the egg until it reaches the complete form of the species.

Pedicella´riæ: Small spines which have divided ends, like scissors or forceps.

Stone-canal: A calcareous tube leading from the madreporic plate to the ring-canal.

Water-vascular system: A series of canals which conduct water through the animal. [pg202]

ECHINODERMATA

The echinoderms, although their shapes are very unlike in the different classes, have the same general internal structure, and also other features which place them together in one group. They are radiates (page 113) of the highest type; they have an exoskeleton; and many of them are beset with spines, from which the name is given. They have locomotor organs, the ambulacra, and a water-vascular system peculiar to themselves. Some have the very strange power of casting off, and developing again, parts of the body.

The development from the egg to the adult is remarkable, and of unusual interest to naturalists. The larval stage of echinoderms is so unlike the mature animal that for a long time the larvæ were thought to be another class of animals, and therefore were given the names which they still retain.

In observing echinoderms it will be seen that the dorsal part is carried uppermost by some, such as the starfishes and sea-urchins. In the former the back is broad and extended; in the latter it is curved and contracted. But in crinoids the back is carried downward and is extended like a stalk; in the sea-cucumbers (holothurians) the dorsal and ventral surfaces are parallel with the long axis of the cylindrical body, instead of being on a plane with the mouth and excretory opening. Owing to the unusual positions of the dorsal and ventral surfaces, the terms oral (mouth side) and aboral (side opposite the mouth) are generally used in describing these species.

The surface of the body is divided definitely by the ambulacra, the ambulacral zones, and the interambulacral spaces, but differently in the different classes. The movement of the animals is [pg203] effected by means of the tube-feet, or ambulacra. These have suckers, which are attached or released by the power of the water-vascular system. The madreporic plate, which can be distinctly seen in starfishes at the angle of two of the arms, is a calcareous porous plate which opens into the stone-canal. This canal passes through the body and opens into a circular tube which runs around the mouth. A system of canals extends from this circumoral tube, or ring-canal, and eventually one canal opens into each tube-foot. Water, entering by the madreporic plate, passes through the various canals and into the tube-feet, which it distends. When the feet are pressed against a substance and the water is withdrawn, a vacuum is formed, which causes the disk-ends of the feet to act like suckers. When the feet are again flooded the hold is relaxed. Thus the animal drags its body along with a slow, gliding motion. The madreporic plate, being calcareous, is said to act as a filter, purifying the water as it passes into the body, which it furnishes with oxygen as well as with locomotive power.

A curious organ found in the Echinoidea (sea-urchins) is called Aristotle's lantern. It is a complicated arrangement, not fully understood, having forty parts, and is connected with the alimentary system. One of the parts is the mouth, over which five teeth project. These teeth grasp and grind the food. The exoskeleton is composed of plates of carbonate of lime, called ossicles, which cover the surface of the body. The ossicles are of various sizes and shapes, and are one of the determining features in classification. They may be scattered spicules of lime, separated plates joined by connecting rods, or overlapping plates; or they may be fitted together so as to form a continuous shell. The starfishes are usually carnivorous, the sea-urchins usually vegetarian, while the holothurians, after the manner of worms, take in sand and mud, deriving their nourishment from the organic particles contained in them. All echinoderms live in the sea. [pg204]

CLASS ASTEROIDEA THE STARFISHES

These animals are named from their star-shaped outline. Some have five long, spreading arms diverging from a small disk, which is hardly more than their point of union; others have a large body with short arms, which are like angular projections of the body, giving a pentagonal shape. Some genera have a greater number of arms than others; Solaster has eleven to thirteen, and Heliaster (the sun-stars, found on the west tropical coast) has thirty to forty.

The mouth of the starfish is in the center of the ventral side. A ventral or ambulacral groove extends through each arm. In these grooves the ambulacra, or tube-feet, are arranged in rows. The ambulacra are hollow, cylindrical bodies, each of which has a sucker at one end, and is connected at the other end with a little globular body, the ampulla. The ventral groove forms a ridge in the body-cavity. It is called the ambulacral zone, and is formed by a double row of elongated plates, which meet and form a raised line along the middle of the inside of the arms, and appear like ribs; between them lie the ampullæ. These plates are called the ambulacral ossicles. Numerous other ossicles extend over the surface, buried in the integument of the body, making a calcareous network, or exoskeleton. The ossicles are connected by muscles so that the animal is not rigid, but is able to bend the body and even creep through comparatively small places. The ossicles are covered with spines of two kinds. The very minute ones are the pedicellariæ, and have a jointed end which opens and shuts like a pincers. Their principal use seems to be to remove waste matter or other substances from the body, keeping it free and clean. The pedicellariæ are arranged, in some species, in circles around the [pg206] bases of the spines, and form groups over the dorsal surface. Examining the backs of different starfishes with a strong magnifying-glass, one will be surprised to see the varied grouping of the spines and pedicellariæ. At the extremity of each arm is a red eye-spot, which is sensitive to light, and a tube-foot, which has no sucker and which is believed to act both as an olfactory and as a feeling organ. The madreporic plate lies at the angle of two of the arms or rays. Water filters through the madreporic plate and passes by the stone-canal to the ring-canal around the mouth, and thence to the radial tubes, one of which extends through each arm and is connected by a branch with each tube-foot. At the base of each tube-foot there is a globular reservoir, or ampulla. A valve connects the tube-foot and ampulla. When the ampulla is contracted, water is forced into and distends the tube-foot; when the ampulla is distended, it withdraws the water from the tube-foot, thus acting like a suction-bulb. When water is sent into the tube-feet they are greatly extended and are then placed against an object. The water being then withdrawn through the ampullæ, a vacuum is formed, and the suckers are tightly attached. By the alternating movements of the ambulacra the animal is dragged slowly along and moves with a gliding motion. It does not deviate from a straight path, going over elevations or through depressions without turning aside; its body conforms to the irregularities of the road and never bridges over spaces. The stomach extends a little way into the arms, and a short intestine leads to the excretory opening in the center of the back. Starfishes are carnivorous and voracious, and are particularly [pg207] destructive to oyster-beds. The animal fastens itself to a bivalve, and protrudes a part of its stomach, with which it envelops its prey and slowly sucks it out of its shell. When feeding on small mollusks they take them into the stomach directly. Starfishes regain by natural growth parts of the body which may be lost. Sometimes the animal throws off an arm to escape capture, and self-mutilation also occurs where unfavorable conditions exist. Oystermen formerly were ignorant of the starfish's wonderful powers of regeneration, and were in the habit of cutting up those captured in their forks and throwing them overboard, thus increasing the number instead of destroying their enemies, as each arm with a piece of the body attached to it will, it is said, become a new individual. This tenacity of life makes starfishes difficult to destroy, and they are exceedingly plentiful in all seas. One naturalist speaks of seeing on the coast of Maine a bed of starfishes which extended several miles and covered the bottom so closely that he picked sixty individuals off a small stone. On the northern shores of the Pacific coast they abound in great variety, and some are of unusual size. Asterias gigantea of this region measures two feet across. Another species, Phyncopodia helianthoides, measures a yard in diameter, and has twenty or more arms. The most common species of the Atlantic coast are Asterias vulgaris and A. Forbesii; the former ranges from Long Island northward, the latter from Massachusetts to Florida. These are the species particularly destructive to oyster-beds. Asterias vulgaris sometimes grows to be fifteen inches in diameter; from this, which is perhaps the largest, are found starfishes of all sizes down to the very small Cribrella. They inhabit all varieties of bottoms, from low-water mark to deep water. They are not always abundant in the same place, but seem to move about.

Some oystermen believe that the starfishes get into masses like a ball and are rolled along by the tide. This idea comes from the fact that an oyster-bed may be free from them one day and the next be covered by these pests. To get rid of them the beds are swept over with a tangle, which is an iron bar holding swabs of raveled rope. The spines of the starfish are caught in the [pg208] tangle, and often hundreds are brought up in one haul and are then killed by steaming.

The anatomical system of the starfish is easily traced by cutting off, with scissors, the skin from the dorsal surface of the disk, and also cutting a slit down one of the arms. In the center of the body will be seen the upper part of the stomach, a small star-like spot, from which radiate five branches, which divide and lead into the much-ramified, plume-like organs which extend through the arms. These are the pyloric cæca, whose function is to secrete the digestive fluids. The much-folded stomach occupies the greater part of the central space, its large convolutions showing on top. The mouth connects with the stomach on the ventral side. By turning back the skin from the arm, small filiform processes can in some large species be seen; these are the dermal branchiæ, or breathing-organs, which may either project through pores in the skin between the ossicles or be entirely retracted. If the pyloric cæca be laid back, one can see the rib-like arrangement of the ambulacral ossicles, and also the ampullæ, which lie between the ossicles on each side of the ridge. If an ampulla be inflated and then pressed, the corresponding tube-foot will be seen to extend. To follow successfully the water-vascular system, beginning in the madreporic plate and extending through the stone-canal to the ring-canal around the mouth and thence through the arms, requires a strong glass and more skilful manipulation.

ORDER PHANEROZONIA

Family PORCELLANASTERIDÆ

Family ASTROPECTINIDÆ

In this family there are only two rows of tube-feet; the rays end in sharp points and have large ossicles on the margins. [pg209]

This genus of starfishes is celebrated for its peculiar habit of breaking in pieces when taken from the water, and therefore good specimens are almost impossible to obtain.

Family PENTAGONASTERIDÆ

Family ANTHENEIDÆ

Family PENTACEROTIDÆ

Family ASTERINIDÆ

The starfishes of this family are pentagonal, with a large body and short arms. The disk is more or less elevated in the center, and the edges are sharp. There are two rows of ambulacra. The ossicles are notched and overlapping. The family is confined to temperate and tropical waters.

ORDER CRYPTOZONIA

Family SOLASTERIDÆ

Family ECHINASTERIDÆ

Family HELIASTERIDÆ

Family ASTERIIDÆ

The Asteriidæ have the following characteristics: four rows of tube-feet; ossicles small and unequal; spines isolated or grouped; pedicellariæ of two forms, forceps-like and scissors-like respectively. They include the very common forms found on all beaches.

CLASS OPHIUROIDEA BRITTLE-STARS

The ophiurans, or brittle-stars, differ from the starfishes in having the arms quite distinct from the body. In starfishes the arms are extensions of the body, and the viscera extend partway into them, while in ophiurans the body is a central disk, with the five narrow arms attached to its margin. In form they suggest a spider, and sometimes are called sea-spiders. The name brittle-star is also descriptive, since they break off their limbs readily. The arms are narrow, taper to a point, usually curl at the ends, and have no ambulacral grooves, but are completely covered with bare calcareous plates (except in the first order, where they have a skin and no plates). The ambulacra are small spines without suckers, which emanate from the sides or margins of the arms and do not serve for walking. The madreporic plate is on the ventral surface, in one of the circular shields which surround the mouth. The alimentary canal ends blindly. The egg-sacs lie between the arms and open by slits on the under side, close to the arms, where they join the disk. Water flows in and out of these pouches, which are thought to have also respiratory and excretory functions. No eye-specks have been found, but they must exist, since the animal is sensible to approaching danger and quickly retreats. The ophiurans are more active than starfishes, moving by wriggling, and clambering with their arms. They are shy and hard to find, and it is difficult to capture a whole one, since they throw off pieces of their arms at the least alarm. Often they completely dismember themselves, an action which does them no permanent injury, since they reproduce lost parts. They are more commonly inhabitants of deep than of shallow waters, and are brought up from the bottom in dredges in great numbers. [pg215] Some species may be found near low-water mark under stones and in clusters of mussels, and often in seaweeds, thrown up from deep water, on the shore.

ORDER EURYALIDA

ORDER OPHIURIDA

CLASS ECHINOIDEA SEA-URCHINS, CAKE-URCHINS, HEART-URCHINS

ORDER DESMOSTICHA SEA-URCHINS

The shell of a sea-urchin consists of many calcareous plates, or ossicles, fitted closely together and forming a continuous exoskeleton. The plates are so united that externally the marks of juncture are not perceptible, but on the interior the shape of these plates is well defined. In examining such a shell, or test (they abound on the beach), it will be seen that its surface is covered with numerous hemispherical projections or knobs, which are grouped in double rows and run in meridional lines from one pole to the other of the more or less spherical body, separating it into ten divisions. Five of these divisions have perforations, or small pores in the plates of the shell, and are called the ambulacral zones or areas, because through these pores pass the small tubes, in the living animal, which connect the tube-feet, or ambulacra, with the radial water-canals and the ampullæ (see page 206). The wide spaces between these double rows of pores are called the interambulacral zones or areas. The ten spaces diverge from the peristome, or soft part around the mouth, in the center of the lower surface, and converge in the small area at the top or aboral side. In the center of this small circular dorsal space is the excretory opening, and surrounding it are ten plates, five of which have openings into the egg-sacs. One of them is larger than the others, and is modified to form the madreporic plate. The other five plates have eye-specks. The ambulacral zones terminate at these ocular plates.

The numerous spines which cover the animal are of three [pg219] kinds, and proceed from the knobs on the exoskeleton, over which they fit, forming ball-and-socket joints, which enable them to move in any direction. The long spines are ribbed, and seem to have no other function than that of protection. The second set, the pedicellariæ, are very peculiar small organs scattered over the surface in great numbers, and consisting of a head bearing three bill-like blades mounted on a long, flexible stalk. The office of some of the pedicellariæ is to remove waste from the excretory opening; this is passed down regular lines and dropped into the water, thus keeping the body clean. Others are constantly opening and shutting their forks, reaching in all directions and grasping and removing anything which may have become entangled in the spines. They also capture floating bits of seaweed, which they drag over the body to conceal it. A third set of projections are the sphæridia, small globular bodies said to be connected with perception.

The spines vary greatly in size, number, and form in different species, and are such conspicuous features as to make the identification of species easy. In some the spines are solid and fluted; [pg220] in others they are hollow, sharp, and brittle; again in others they are short and silky, or very long and serrated, and so on. In one species they are so broad and flat as to resemble little sails. (See Dorocidaris.) (Plate LVI.)

The mouth, over which five long teeth project, is a part of Aristotle's lantern, which forms a curious and prominent feature in the center of the lower surface. Ten tentacles, like large tube-feet without suckers, lie around the mouth. The alimentary canal, starting in Aristotle's lantern, winds in two and a half coils around the inside of the shell, supported by mesenteries, and terminates in the excretory opening on the aboral surface. The sea-urchin has also a water-vascular system similar to that of starfishes (page 206). When the tube-feet are distended they project beyond the spines, and enable the animal to move slowly about; but sea-urchins are less active than starfishes, and although they are so well protected by spines and have few enemies after maturity, they lie in sluggish idleness in secluded places, and for further concealment often cover themselves with seaweeds or stones.

The sea-urchin has a nervous system, which starts in a ring around the mouth, ramifies through the body, and terminates in the eye-plates. The tube-feet and all the spines are under nervous as well as muscular control. Egg-sacs lie under the apex of the shell and open by separate ducts into the five plates on the small upper disk. Through these the eggs are discharged into the water, where they become free-swimming larvæ, called Pluteus. This immature sea-urchin (Pluteus) undergoes several curious transformations in the course of its development, and does not in any way resemble the mature animal. In spring the apical disk of the females will often be found covered with orange-colored ova, and that of the males with white sperms. In the growth of the animal, in its mature form, the shell enlarges by accretions of lime on the individual plates, or ossicles, of the exoskeleton, and by new plates formed around the apical disk. Sea-urchins are compared to starfishes folded over, the eye-specks on the ends of the rays meeting in a small area around the excretory opening, the ambulacra following spherical lines and leaving the mouth, as before, on the ventral side. [pg221]

The Echinoidea present great differences in shape, being more or less spherical, oval, discoid, and heart-shaped. These variations are associated with the differences of internal structure, the openings of the digestive tract being at the opposite poles in the spherical and oval forms, but excentric in the disk- and heart-shaped species. The sea-urchins are grouped in three orders in accordance with these variations. All are characterized by the absence of arms, by having the calcareous plates immovably united to form a firm test, and by the great development of the movable spines upon the plates.

Sea-urchins are sometimes called sea-eggs, perhaps from their shape, but possibly from the edible quality of some species, which are eaten by the natives of the shore, who take them at the spawning season, when the egg-sacs are distended. They are gregarious, and frequently are so crowded together as literally to pave the surface of rocks and the bottoms of tide-pools in sheltered places. The following is quoted from A. Agassiz: "Many of the Desmosticha along coasts exposed to the action of the waves live in cavities which they hollow out of the solid rock. This they do, not by means of any solvent, but by mere mechanical action. They chisel out with their teeth the solid rock by incessant turning round and round, and keep their cave, where they are frequently prisoners for the rest of their existence, up to the size required by the growth of their test and spines, by constant gnawing. On the coast of California the common Strongylocentrotus purpuratus occurs in this way. We find long tracts of shore, where this sea-urchin is common, completely honeycombed and pitted by cavities and depressions in which they seek shelter against the powerful surf continually beating against the rocks. The same species does not excavate in sheltered places, where the sea-urchins can find protection between the interstices of large fragments of rock or ledges more or less sheltered from the more direct action of the open sea."

Sea-urchins in cavities of granite rock, where the openings are too small for the animal to get out, are to be seen in thousands on the coast of France at Croisic, Lower Loire. Spines of large sea-urchins are used as slate-pencils by the missionaries in the Pacific Islands. [pg222]

Family CIDARIDÆ

Family ARBACIADÆ

Family DIADEMATIDÆ

Family ECHINOMETRIDÆ

Family ECHINIDÆ

ORDER CLYPEASTROIDEA CAKE-URCHINS

The animals of this order, commonly known as sand-cakes or sand-dollars, are flat and circular like disks. Sometimes they are cut at intervals on the margin; again they have slits through the body (lunules). They have a well-marked star-shaped figure on the dorsal surface. This figure is formed by the ambulacra, or tube-feet, which run in five rounded or petal-shaped lines on the under surface. The mouth, in Aristotle's lantern, is in the center of the somewhat concave ventral surface, the petal-like ambulacral zones meeting at the central space. The excretory opening is on the margin of the disk, at a point between two of the sections of the star-like figure. This marks the posterior part of the body, while the opposite arm of the star marks the front or anterior end. The spines are very fine and silky, and are spread abundantly over the whole animal. Clypeasteroids are mainly found in sand considerably below low-water mark, though some species thrive where they are exposed to the surf on open sandy beaches.

Family ECHINANTHIDÆ

Family SCUTELLIDÆ

ORDER SPATANGOIDEA HEART-URCHINS

The Spatangoidea, or heart-urchins, have heart-shaped or thick elliptical bodies. The mouth and excretory opening are both away from the center and on the ventral side. These animals seem deformed, so much are they out of symmetry and so different in outline from the other orders of the class. The ambulacral zones are in circles, or petaloid in outline, as in cake-urchins, but are not continuous, and the anterior one is usually unlike the others and frequently without pores. The entire body is covered with spines, and these are the chief organs of locomotion; the greater part of them turn backward, giving the living animal the semblance of a porcupine. The mouth is protected by a projecting plate, but Aristotle's lantern is absent in this order. The anatomy is in general the same as in the other orders, but the organs are turned in conformity with the inclosing shell. Most of these animals bury themselves in sand or mud and live in deep water; a few only are littoral species.

Family SPATANGOIDÆ

CLASS HOLOTHUROIDEA SEA-CUCUMBERS

The holothurians, or sea-cucumbers, although in appearance quite unlike starfishes and sea-urchins, have the characteristic ambulacral zones and other features of the group. In form they are cylindrical, and, when the tentacles and tube-feet are retracted, resemble fat worms; when fully expanded they are somewhat like sea-anemones, the tentacles forming a rosette-like top. The walls of the body are tough and muscular, with small calcareous deposits or spicules of various shapes in the skin. The mouth is at one end, the excretory opening at the other, and along the body are double rows of tube-feet. Often instead of tube-feet, or together with them, are conical processes without suckers. The ambulacra, when arranged in regular zones, are used for locomotion only in the lines running from the madreporic plate. In some species three of the zones are near together, and form a kind of sole on which the animal creeps; again the tube-feet are wholly suppressed, as in Synapta. Besides progressing by means of these suckers, the holothurians move, as do worms, by the extension and contraction of the body. The inner surface of the tough membrane inclosing the body is lined with powerful longitudinal and transverse muscles, by means of which the creature contracts and lengthens its body and changes its form in a wonderful manner. Around the mouth are tentacles, which are often much branched and are used as organs of touch and smell, and sometimes have an ear-sac at the base. From the mouth the food-canal, making one long coil, extends to a chamber [pg231] (cloaca) at the other pole. The cloaca gives off a pair of much-branched respiratory trees, which are constantly supplied with water by the contractions of the cloaca. At the base of one of the respiratory trees are singular structures known as Cuvierian organs. They are numerous, viscid, glandular tubes, which the animal can throw out, and which will adhere closely to almost anything. The holothurian has a water-vascular system, the madreporic plate being near the mouth, but not opening to the outside, and a nervous system which starts from a ring which lies around the mouth. The egg-sacs are branched tubes, often highly colored, which open to the outside, close to the wreath of tentacles surrounding the mouth.

The larvæ, when free-swimming, are called Auricula. In the deep-water species, Cucumaria crocea and Psolus ephippiger, the eggs, when discharged, and the young are carried on the back of the mother. In Cucumaria lævigata there is a brood-pouch, while in Synapta viviparia the young develop in the body-cavity.

The holothurians have the singular power of ejecting the whole of their internal organs and of growing them again in case they escape the enemy they have endeavored to elude by this strange method. They also turn themselves inside out, as it were, as if from nausea, when confined in water too stale for their uses. Often the viscera are ejected through holes in the sides of the body broken by violent muscular contractions.

Holothurians are generally distributed through all seas, but are congregated in greatest numbers in Eastern seas. Their habitat extends from shallow to very deep water. They are found in tide-pools, on rocks, and in sand or mud. Like worms, they live on organic particles contained in mud and sand, which they take into the gullet and pass through the alimentary canal.

ORDER PEDATA

ORDER APODA

CLASS CRINOIDEA FEATHER-STARS AND SEA-LILIES

The crinoids are inhabitants of deep water, where they grow in great numbers, forming beds of sea-lilies. Their general form, which suggests the lily, and their feather-like manner of branching, give them the two common names of sea-lilies and sea-feathers. They have a long, jointed stalk, one end of which is attached, while the other bears the disk of the animal. From the disk emanate five arms, which divide near the base, making [pg235] ten arms in all. The arms have short branches along the sides. Ambulacral grooves follow the center of all the arms and branches. The mouth is in the center of the upper side, which in this case is the ventral surface. The genus Pentacrinus remains permanently attached, but Comatula, at a certain stage of development, separates from the stalk and swims freely about by means of its arms. It can attach itself temporarily by tubular processes, which are developed on the dorsal surface at the point where the stem was attached. The ossicles, or plates which cover the dorsal surface, are free, making the crinoid an animal of innumerable joints.

The crinoids are particularly interesting from the fact that they have existed from early geologic times, and their history is written in stone. In the early ages they were the only class of echinoderms, and their evolution into other forms can be traced through successive geologic periods. They existed in such vast numbers that the fossil forms are plentiful and are familiar to every student of geology, and are known as stone-lilies and encrinites. To-day they are decadent, there now remaining only twelve of the two hundred genera which existed formerly. A fine bed of crinoids is found off Cuba, on the slope of the coast where the water rapidly deepens from one hundred to two hundred fathoms. [pg236]

Although the crinoids are deep-water forms, and are never found on the beach, they are given here because they follow in the system of classification and illustrate another curious class of echinoderms. The brief description given may add interest to the fossil forms to be seen in museums.

TERMS USED IN DESCRIBING CRUSTACEA

Epime´ra: Divisions on the ends of the segments of amphipods and isopods, and belonging to the legs.

Exop´odite: The outer one of the two main branches into which the typical limb of any segment is divided.

ARTHROPODA

This subdivision of the animal kingdom includes insects, centipedes, spiders, and crustaceans, which together constitute more than half the known species of animals. Although these animals are so unlike in general appearance, it is easy to recognize the common characteristics which place them together in one group. The name Arthropoda, meaning "jointed-footed," suggests perhaps one of the most obvious points of resemblance. The Arthropoda have bilateral symmetry, one side of the body being like the other; they are covered with a horn-like material (chitin); they are divided into segments; the segments have appendages; and the appendages are jointed so as to admit freedom of motion. Their manner of growth is peculiar; they cast off their rigid external coverings and secrete larger coats of mail, and at these periods increase in size or undergo metamorphosis.

There are such modifications of these general features as the habits of the different species demand. For instance, the appendages may be constructed for walking, swimming, boring, sucking, or the seizure and preparation of food. In some animals the appendages form a part of the breathing-organs, in others are used as organs of sense. Every detail of the organism, down to the hairs, has its special use and function.

CLASS CRUSTACEA

The crustaceans vary in size from microscopic minuteness to two feet or more in length. The giant crab of Japan (Kaempferia kaempferi) exceeds this, being commonly from eight to twelve feet [pg245] across the arms, and is said to reach even greater proportions. Crustaceans live on land and sea, and in both fresh and salt water; they may be parasitic, sedentary, or free and active. There are said to be over ten thousand species, which include crabs, lobsters, shrimps, beach-fleas, wood-lice, barnacles, and water-fleas. Nine tenths of the species are marine; of these some are pelagic, and their transparent forms constitute a part of the plankton. Others live on the bottom in deep water and attain a large size. A vast number live in the littoral zone and form a considerable part of that crowded community. They are scavengers and freebooters, being great fighters, as well as predatory in their habits. As a rule, they feed on dead organic matter, which they consume in surprising quantities; some have also a vegetarian diet. They have, like starfishes, the singular power of throwing off their limbs and growing new ones.

The Crustacea derive their name from the nature of their crust or covering. This is earthy and brittle, not stony, like the shells of mollusks. This crust, or exoskeleton, has various degrees of firmness, from that of a delicate polished cuticle, seen in small forms, to the heavy armor of some crabs and the shell-like character of the covering of barnacles.

The lobster and crab are perhaps the most comprehensive examples as well as the largest in size of the class, the vast majority of the species being minute forms. The ocean swarms with varieties too small to be noticeable to the naked eye.

It is the province of Crustacea to consume decaying organic matter, both animal and vegetable, and in doing this they perform a great service in purifying the waters of the pool, the shore, and even the sea. Not only in this are they serviceable, but to a great extent they serve as food for other animals, their flesh being palatable and preferred to that of other animals whose diet would seem to make them more wholesome. The small forms exist in such myriads, and increase so rapidly, that, although extremely small, they furnish an inexhaustible supply of food. Even some whales subsist upon these minute animals, and for man the larger species are articles of diet that are counted among the luxuries. The crustaceans are remarkable for their varied forms and for their [pg246] perfect adaptation to many different conditions of life. There is no class in the animal kingdom which presents so wide a range of organization, or whose structure deviates so widely from the type form. These differences lie chiefly in the external characters and in the structure of the appendages.

Some species are solitary, like lobsters and crabs; others, like shrimps, are gregarious and live in immense shoals. In the habits of these animals there is much which excites wonder and interest.

ANATOMY OF THE HIGHER CRUSTACEA

The body of a crustacean is divided into segments, which are sometimes distinctly separated, like joints, and sometimes fused into one piece. The head part is called the cephalic portion, the middle section is the thorax, and the posterior part is the abdomen. The horn-like covering of the thorax is the carapace; where it projects over the head it is the rostrum. When the head and thorax are united, as in most Crustacea, the anterior or front portion of the animal is called the cephalothorax. Each segment has a pair of appendages. Each appendage has a joint attached to the body; from this arise two jointed branches, the endopodite and the exopodite, the inner and the outer foot. The appendages are modified to perform special functions. In front of the mouth are two pairs: the smaller ones are the antennules and have ears at the base; the larger ones are antennæ and are feelers. At the base of the antennæ are the green glands, said to have renal functions. Both the antennules and the antennæ are fringed with hairs, which aid in the sense of touch and perhaps of smell. On each side of the mouth are the mandibles. Then come the maxillæ and the maxillipeds, used in capturing and tearing the food and conveying it to the mouth. Thus it will be seen that some of the appendages around the head are connected with the senses, and others are used in eating. Those of the thorax are for walking; those of the abdomen for swimming, guarding the eggs, etc. The food taken into the mouth passes into the stomach through a short passage. The stomach is divided into two parts. The front [pg247] one contains three long teeth which meet laterally and grind the food; this is known as the gastric mill.

When sufficiently fine, the food passes through a strainer of stiff bristles into the smaller portion of the stomach, where it is partially digested, and from there enters a long, straight intestine which reaches the length of the body and opens to the outside on the under side of the telson, or last segment. A large liver also pours its secretions into the intestine. The green substance commonly called "fat" in lobsters is the liver.

The heart consists of an elongated tube, or a short sac, which lies directly under the integument of the back. From this heart-sac, blood, which is colorless, is sent by arteries to all parts of the body; it then collects in spaces called venous sinuses, from which it goes to the gills, and thence back to the heart.

The nervous system begins in a large ganglion in front of the mouth, called the brain; from this two branches arise, which pass on each side of the digestive organs, meeting in ganglia in each segment and extending the whole length of the body. The gills, by which the animal breathes, are upon the limbs, or on the walls of the body immediately adjacent to them, and are generally inclosed in special chambers. In lobsters and crabs two such chambers are found under the flaps of the carapace, above the walking-legs. Gills are divided so as to present much surface to the water, from which they absorb oxygen. They are like a dense mass of little tubes arranged along a central tube. The class has two kinds of eyes, simple and compound; the latter are composed of a number of eyes. In some species the eyes are placed on the ends of movable stalks, which enable the creature to see in all directions and from a higher plane than the body occupies. As a rule, the eyes occur in the head region, but in the shrimp Euphausia they are on the thorax and abdomen. In barnacles simple eyes exist in the young stage, but in adult forms there are no apparent visual organs. The ear (so called) consists of a sac containing small silicious particles suspended in fluid. Numerous fine hairs on the inner surface of the sac connect with nerve-fibrils.

The organs of hearing are in various places. In decapods, or the larger Crustacea, they are at the base of the antennules. [pg248]

The muscles are white bundles of fibers, and are in strips, which is an indication of power and activity. There are four important sets: twisted ventral muscles which bend the tail and are particularly large and strong, those which straighten the tail, those moving the appendages, and those which work the gastric mill.

The eggs, after being discharged, are attached to the abdominal legs of the mother by a kind of cement, or they are carried in pouches attached to the thorax. In these positions they mature, and hatch at different stages of development in different species. Some emerge with three pairs of legs, and are known as Nauplius; some are Zoëa, having a carapace and abdominal segments, but no abdominal appendages. Another stage is Megalops, with large stalked eyes. Others are hatched as miniature adults. These names were given when the embryo stage was not recognized and the larvæ were thought to be distinct species.

The growth of the animal is effected by moulting. The Crustacea are named from the crust-like covering which envelops them. It is a horny material, called chitin, in which are deposited particles of carbonate of lime, making a rigid envelop which would prevent all freedom of motion, were it not that there are spaces free from lime, and thus flexible joints are left. When the animal expands it throws off this hard covering and secretes a new and larger one. As the time of moulting approaches, the old covering becomes loosened, and a delicate new one is formed beneath it. The old shell splits open across the back just behind the carapace, and the soft animal withdraws first its cephalothorax and then its abdomen, leaving the cover complete, including even the covering of the eyes and the lining of the stomach. The [pg249] new shell is rapidly hardened, being already formed when the old one is cast, and the animal regains its normal condition in about a week; in the meantime it is defenseless, and lies quiet in some secluded place. Moulting is an exhausting process, and is attended with great dangers. A great mortality occurs at this time from accidents, from weakness, and also from helplessness in case of attack.

The hair-like processes scattered over the shell, often like fringes, are said to be organs of feeling.

SUBCLASS ENTOMOSTRACA

These are Crustacea of small, often microscopic size, of comparatively simple organization, and with appendages adapted to serve the purpose of respiration. These minute animals may be obtained by skimming the surface of the water with a muslin net, preferably at night, then washing off the inside of the net with a small quantity of water into a glass dish. Place the dish on a dark surface before a light, and the little creatures will gather toward the light, and may be satisfactorily observed with a glass.

This order, though composed of minute forms, is one of great economic importance, from the fact that the little crustaceans exist in vast numbers and furnish a very considerable part of the food of many fishes. Cyclops is the most common of the fresh-water, and Cetochilus of the marine genera. These, together with other genera, swarm in water wherever life exists, from the smallest pools and ditches to the broad surface of the ocean. Without having drawn a surface-net on some sheltered bay, it is difficult to have an idea of the myriads of Entomostraca in the sea. Although nearly transparent and of such delicate texture as to be almost jelly-like, they sometimes color the sea with a reddish tint for miles. Whales which have baleen, or fringes of whalebone, in the mouth subsist on these small organisms, which are called "brit" by the whalemen. The whales, sometimes in schools, rush through the water with open mouths, engulfing these little [pg250] crustaceans, the baleen straining them from the water. Although devoured in such immense quantities, and sometimes lying dead in sheets of scum on the surface of the water, they maintain their numbers by the exceeding rapidity with which they reproduce. It has been computed that the descendants of one Cyclops may number in one year 4,500,000,000, provided all the young reach maturity and produce a full number of offspring.

One of the free marine forms, Sapphirina, is of especial interest, as it surpasses all animals in phosphorescence and sparkles by day as well as by night. It is one quarter of an inch long, and is broad and flat.

Besides the myriads of free-swimming copepods, there are parasitic forms in great number. The marine parasitic forms are commonly known as fish-lice. They have various habits, some living as commensals, others attaching themselves to animals only to be carried about; the true parasites live upon the blood and tissues of their hosts, and may fasten themselves to the external parts of the body or to the internal organs. Whales, fishes of all kinds, mollusks, starfishes, jellyfishes, and corals, all have some form of parasite, and many have several different kinds of guests. It is said that the haddock has more than a dozen which infest its external and internal membranes.

Nicothoë is found on the gills of lobsters. The truly parasitic forms are usually very degenerate and lose the characteristics of their order.

Barnacles of the genus Balanus (acorn-shells) (Plate LIX.) are familiar objects on rocky shores, which they often whiten with their shells, and those of the genus Lepas are also widely known. The name of the order is descriptive of their curled appendages. The appendages are fringed like feathers and are drawn into or protruded from the shell at will. When extended they are constantly in motion, and create currents which carry food to the [pg251] mouth of the animal, which is dependent upon such food as comes within range of its tentacles.

Their life-history is interesting. The young barnacle, called a nauplius, in no way resembles the adult. When it emerges from the egg it is a free and independent animal, with one eye, three pairs of legs, and a single shell. It swims about for a while and moults several times. It then has two eyes, two shells, and six pairs of legs. At this period it seeks a permanent home, and attaches its anterior end to the object it selects by means of its antennæ, which have become suckers. It makes its hold secure by secreting a cement which permanently fastens it to the spot. It then undergoes metamorphosis, loses its bivalve shell and its eyes, and attains its characteristic cirripeds, or curled feathery legs, and a new shell covering. During these transformations, from the time it becomes fixed until it attains its adult form, the barnacle fasts, living by the absorption of its own animal fat. Its food subsequently consists of the minute animal forms which abound in the sea. Its further growth is by moulting, but parts only of its covering are disengaged; the shell is permanent, and its successive stages of growth are marked upon it by lines, as in mollusks. The lining of the shell, or enveloping skin of the animal, and also the cuticle of the legs are [pg252] shed, and in the spring of the year these thin, glossy casts are found in abundance floating on the surface of the water near the shore.

There are but three orders of barnacles, namely, those in which the shell is directly attached to the rocks, those which are attached to floating objects by a long stalk, and those which are parasitic on animals. A species of the third order infests the whale.

The older zoölogists classed barnacles with the Mollusca, but in 1829 Vaughan Thompson, in the study of their embryology, found that they should be classed with crustaceans, in company with crabs, shrimps, and water-fleas, with which their immature forms show direct relationship.

This genus is commonly known as the ship-barnacle, also as the goose-barnacle. It attaches itself to floating logs as well as to ships, but the latter form its principal home; consequently it is a great voyager, and, though common everywhere, is everywhere considered a stranger. The same species are found on ships coming from the most remote and widely separated regions, and so they cannot be considered native to any one locality. They are wanderers on the deep, and grow in such numbers on the bottoms of ships, especially of those which sail in warm seas, that they seriously impede the progress of the vessels. Aside from diminishing its speed, they do a ship no injury.

There was a tradition, which lasted several centuries, that geese were hatched from these shells, which somewhat resemble eggs. Gerard, in the appendix to his "Herball or Generale Historie of Plants" (1597), gives a picture of shells of Lepas growing on a tree, with geese falling from them and swimming about in the water below. His description is as follows: "There are founde in the North parts of Scotland and the islands adjacent called Orchades certaine trees whereon do growe certaine shell fishes of a white color, tending to russet, wherein are conteined little living creatures; which shells in time of maturitie do open, and out of them grow those little living foules whom we call barnakles, in the North of England brant geise, and in Lancashire tree geise; but [pg253] the other that do fall upon the land do perish and come to nothing." He then describes in detail the various transformations, and ends with: "But what our eies have seen and hands have touched we shall declare."

The long, flexible stalk of Lepas is its anterior end. Generally this stalk is only half an inch long, but in some species it attains the length of a foot.

Huxley describes the barnacle as a crustacean fixed by its head and kicking food into its mouth with its legs. The mouth has a pair of small mandibles and two pairs of maxillæ, the last pair uniting to form a lower lip. The thorax has six pairs of branched appendages. The body is enveloped in a fold of skin, to which are attached five shell-like plates. One of these plates is long and narrow, and extends along the dorsal side; two are large and triangular (the terga); two are small and triangular (the scuta), the long point extending downward. These shells are on the free or posterior end.

Barnacles have a nervous system, consisting of a brain and a chain of five or more ganglia, but no special respiratory or circulatory organs are known; the cirripeds, or feet, are supposed to perform these functions. They have also a food-canal, a digestive gland, and excretory tubes. The eggs are carried under the external fold of the skin in flat cakes.

Balanus is known as the "acorn-shell," or "sea-acorn," and is found in vast numbers and of all sizes between tide-marks, incrusting rocks and the piles of piers. It also may be found attached to floating objects or to shells, or even to living animals, but its usual habitat is stationary. Unlike Lepas, it has no stalk, the shell being directly attached to some object. The body is surrounded by a fold of skin, to which are attached a shell consisting of six or more plates and a fourfold lid, or operculum, consisting of two scuta and two terga. The operculum may be called the door, as the animal opens and shuts it at will and has complete protection when it is closed. If one taps a rock [pg255] incrusted with barnacles, and holds the ear near, the closing of the many doors may be distinctly heard.

The development of Balanus from the larval stage, as also the anatomy of the adult, is similar to that of Lepas. When covered with water and unmolested, there may be seen over a bed of barnacles thousands of tiny fringed feet waving to and fro. The motions look like gestures; they are perfectly regular and rapid, numbering eighty to a hundred a minute. The shell covering formed by barnacles on piles of wharves and bridges is said to be a protective agent; otherwise the barnacles seem to have no economic value in nature, as, unlike other animals, they do not serve, except in very small measure, as food to other classes. The tautog and perhaps some other fishes feed partly upon them. They are sometimes an obstacle to oyster-culture, as they fasten upon the objects intended for oyster embryos, and, growing faster than the latter, soon crowd them off. One species, Coronula diadema, fastens to the skin of whales. It attains the size of two inches in diameter. The shell is half an inch thick and full of cavities, into which the skin of the whale is drawn, giving the barnacle a secure hold. (Plate LIX.)

These are parasitic forms and very degenerate. Sacculina lives on crabs, and its term of life is about three years, during which period the afflicted crab does not moult. Its shape is that of an ovoid sac on a stalk, which it attaches between two segments of the ventral surface of its host. The stalk divides and ramifies in a root-like manner within the body of the crab, from whose vital elements it absorbs its nourishment. The roots spread like a mycelium through the whole crab, even to the claws.

CLASS MALACOSTRACA

This subclass comprises highly organized Crustacea, usually of considerable size, having the appendages much differentiated, the thorax with eight segments, and the abdomen with seven segments.

The name, meaning "cleft-footed," applies to the appendages of the thorax, which are once-branched (biramous). Gills, when present, are attached to these feet, and hang freely in the water. A delicate carapace covers the thorax; the abdomen is proportionately very large, often twice the length of the cephalothorax. In Mysis the eggs are carried in pouches under the thorax, giving the common name of "opossum-shrimp" to this small, transparent, phosphorescent crustacean.

The Decapoda are named from their ten walking-legs. The higher forms of crustaceans belong to this order. All the Decapoda have a similar anatomy, but are placed in two subdivisions [pg258] according to their external form. In Macrura, the first subdivision, belong the lobsters, crawfish, shrimps, prawns, and hermit-crabs, animals having a long and more or less cylindrical body, with the abdomen extended; in Brachyura, the second subdivision, are placed the crabs, animals having the thorax broad and flat, and the abdomen bent under the thorax. The Decapoda have twenty segments, all of which, except the last one, have, at some period of life, a pair of appendages. The first two pairs of appendages, or, in the stalk-eyed forms, the first three pairs, are especially connected with the senses, and are often fringed with hairs, which are also considered to have a sense-function. The antennules, or first pair of appendages after the eye-stalks, are sometimes divided into two or three branches. At the base of the antennules are the ears. The antennæ, or second pair of appendages, are undivided, but are larger than the first pair, and are often very long. At the base of the antennæ are the renal glands. Both the antennules and the antennæ are slender, elongated, movable, and full of joints. In some species they are greatly modified, as in Scyllarus, where they are developed into broad swimming-plates and, perhaps, as shovels for burrowing; in some amphipods they are used as swimming-organs. (Plate LX.)

The next six pairs of appendages are grouped about the mouth. They are the mandibles, the maxillæ, and the maxillipeds. The mandibles are at the mouth-opening, and, being heavy and hard, are adapted to tearing and grinding; they have a jointed attachment, the palpus, whose office is to keep the mandibles clean. The two pairs of maxillæ are delicate and leaf-like. The three pairs of maxillipeds grow gradually larger, the last pair being very prominent and extending over the other mouth-parts. Next come five pairs of walking-feet. One or more pairs of these feet have pincer-like ends, or claws. Some species have the claws immensely developed, as in lobsters. The claws are the chelæ, and the feet which bear the chelæ are termed the chelipeds. The rest of the walking-feet have generally single, hook-like ends, but are variously modified in different species. The abdominal segments have six pairs of appendages, also variously modified. The last segment is without appendages, but often is extended into a tail, [pg259] or fin-like expansion. The next to the last segment, in many forms, has appendages modified into swimming-plates, which extend on each side of the telson, forming a broad, fan-like caudal extremity.

They have, then, to correspond to the twenty segments of the body, two pairs of sensory, six pairs of mouth-, and five pairs of walking-appendages attached to the cephalothorax, and six pairs on the abdomen. The terminal segment, or telson, is without appendages. The exopodite is present on the maxillipeds, but disappears from the walking-feet in the higher forms.

In moulting the Macrura split in the longitudinal line down the back; in the Brachyura the split occurs across the body at the point between the thorax and the abdomen.

The characteristic features of the Macrura are an elongated body with the abdomen usually extended; a carapace, somewhat cylindrical; and the last pair of appendages of the abdomen (which are attached to the next to last segment) united with the last segment, or telson, to form a powerful caudal fin, used for swimming backward. The creeping forms in moving walk forward, but swim backward.

In these animals the body is compressed and the carapace is not hard. The abdomen is very large in proportion to the cephalothorax, and has a peculiar bend. The rostrum is often longer than the thorax. The eye-stalks, antennæ, and legs sometimes attain extraordinary length, and the chelæ (claws) are not always on the first pair of legs. In some species chelæ are on two or three pairs of the legs. Above the antennæ are expanded antennal scales, which, together with the long bases of the antennules and very prominent eye-stalks, make the head a broad and conspicuous feature. The difference between shrimps and prawns is not very well defined, the small individuals seeming to be generally called shrimps, the larger full-grown ones prawns. [pg260] Prawns are known as crevettes in France and as Garnelen in Germany, where they are largely used as food. In the United States the shrimp-fishery is an industry of the South. On the California coast the fisheries are very extensive and are monopolized by the Chinese.

There are but three species of this genus, which is the most important one of all the Crustacea. They are H. vulgaris of Europe, H. capensis of the Cape of Good Hope, and H. americanus, which occurs on the eastern coast of the United States from Labrador to New Jersey. The lobster-fishery is one of great importance, and of such value that it is governed by stringent laws. The [pg262] annual catch on the Atlantic coast of North America amounts to many millions of lobsters, the money value of which is very large.

Scyllarus has a broad, almost square carapace, which is uneven and coarsely granulated; the anterior corners are sharp, the posterior ones rounded. The antennæ are curiously modified into broad, flat, double plates reaching quite across the straight anterior end of the carapace. The under scales of these modified antennæ are rounded and leaf-like, the upper ones are pointed. The margins of the abdominal plates on the ventral side are toothed, and on the upper side the first three sections have [pg264] knobs, the third one being the most prominent, and forming the posterior extremity when the abdomen is folded in. The walking-feet are all simple and end in points; the first pair are the longest, and the following ones gradually diminish in size. The ventral surface is rough and spiny. The abdomen is of about the same length as the carapace. These animals are found off the Florida coast and are caught in the fish-traps. They are uncommon. The very peculiar development of the antennæ makes them worthy of examination when opportunity offers.

The anomalous forms which are intermediate between the suborders Macrura and Brachyura were, until recently, placed in a suborder, Anomura. The members of this group differ from one another, and some of them resemble in external features members of the other divisions of the suborders, but there is a difference in anatomical structure which separates them in the classification.

In these curious animals the posterior part of the body is not protected by a crustaceous covering, and therefore the animal seeks protection by inserting its soft and defenseless abdomen into some hollow object, usually the shell of a gasteropod mollusk, as the whelk or the periwinkle (Buccinum, Littorina). The hermit-crabs do not always use a shell for this purpose, as they are sometimes found in the tubes of plant-stems or in sponges. Like other organisms in the animal world, they seem [pg265] well fitted to make the best of their surroundings, the body becoming modified to suit the peculiar conditions under which they live. In those which inhabit shells the abdomen becomes spiral, in conformity to the convolutions of the shell. All the abdominal appendages are more or less atrophied; the sixth pair become like hooks, and these fasten to the columella of the shell, keeping the crab securely attached to it. In the female some of the abdominal appendages are hair-like and are adapted to carrying the eggs. The thorax, being protected, is protruded from the shell at will. The first pair of feet are much larger than the others, and are provided with claws (chelæ). The first right foot is usually much larger than the left, and, besides the usual functions of capturing and crushing prey, the claw, or hand, serves as an operculum to close the mouth of the shell when the crab retires completely within it. The small left hand is shaped to fill out the parts of the opening not covered by the right one, thus making a close fit. The next two pairs of feet end in simple hooks, and are used for walking and dragging the crab along when he travels. These crabs move about very fast, and the houses upon their backs seem no encumbrance. [pg266]

In some genera both hands are alike; in others the left one is the larger. In the case of hermits which live in tooth-shells, the right hand is cylindrical in form, fitting the circular opening of the shell. The other extreme is found in the genus Cancellus, where both the chelipeds and the first pair of ambulatory feet are ingeniously shaped, so that when closed they form a round operculum, or door, which closes the way into the compact sponge which this crab has for its carcinœcium, or house. It is interesting to note these differences and observe the perfection with which the feet are formed and jointed to suit the openings of different shells. Some genera show other adaptations to their twisted houses, the eye-stalks being uneven in length and the ambulatory feet unequal on the opposite sides. Besides this, some species are hairy and cover themselves with dirt for further protection. The exposed claws of some hermits have a special armature of spines, which make a fringe of points around the opening of the shell when the crab is withdrawn.

As the hermit grows he is occasionally obliged to find a new or larger shell, and there are amusing anecdotes of the troubles he experiences at these times while house-hunting. Very often he tries several shells before he finds one to fit. There is a tradition, not, however, well authenticated, that if the shell chosen happens to be occupied by its natural owner, the crab tears out and devours the unfortunate occupant. If the desired shell is occupied by another hermit inferior in strength to himself, he proceeds to take possession by violence. He then examines carefully the empty shell, inserting his legs and feelers, and if he decides to occupy it he withdraws his abdomen from the old shell and darts it so quickly into the new one that the act of transference is difficult to follow. After walking about with the new shell it sometimes proves to be unsatisfactory and further search becomes necessary. After it is well domiciled the crab never ventures outside the shell until it is obliged to change again on account of growth, or because some stronger crab dispossesses him. The shells of hermit-crabs serve frequently as the home of other animals which live with them a commensal life. The hydroid Hydractinia polyclina often covers the exterior of such shells with a brown, velvety growth. Some sea-anemones also are commensals [pg267] with hermits. Adamsia palliata is always found on the shell occupied by Eupagurus prideaux, and never on any other. This is a European form. On our own coast a red anemone, the Epizoanthus americanus, found in deep water off the entire eastern shore, fastens on the shell occupied by the hermits Eupagurus pubescens and E. kroyeri. This anemone in time absorbs the shell of its host and itself becomes its protector—an advantage to the hermit, who finds room in the yielding polyp-mass for its increasing size, and feels no longer the necessity for change of domicile. The female hermit holds its eggs in the posterior feet until they are hatched; the young are then released, pass into the water, and soon find shells for themselves.

This genus is represented in Southern waters by several species. One of the most characteristic of them lives in Dentalium, the tooth-shell. The outer surface of the right hand is formed to close the shell. All the ambulatory feet and the very small left hand fold beneath, leaving only the flat surface of one hand exposed to view. Another species lives in a shell covered with polyzoans.

The crabs of this family are little more than one quarter to one half of an inch across the back. The chelipeds are broad and flattened. The first three pairs of walking-legs are well developed, and the fifth pair are very small and are doubled over the base of the carapace. The sixth segment of the abdomen has a pair of biramous appendages, which, with the telson, form a swimming-fan.

The species of this family have a broad, ovate, uneven body and a prominent rostrum. The fifth pair of legs are rudimentary and are folded under the carapace in the branchial chambers, so that the crabs appear to have but four legs on each side. This is the distinguishing feature of the family, and makes them easily recognized.

This group contains the true crabs, which are the highest of the Crustacea. In form they are quite the reverse of the first group. In the Macrura—except in the anomalous forms—the body is long and cylindrical and the abdomen extended, but in the Brachyura the body is flat and broad and the abdomen short and reflexed. Crabs of this suborder inhabit all seas of the globe, and are found from the shore to great depths. Some species live on land, some on the shore, some in deep water. Some forms burrow in the sand; others live under stones and boulders, or conceal themselves in crevices of rocks or in the cavities of sponges. They are divided into many families, and creep, climb, swim, or burrow, their structure being modified to their respective modes of life. There is also great variation in their shapes as well as in their color and markings. This diversity is so great and peculiar that it seems as though each one were more curious than the others.

In crabs the cephalothorax is depressed and often broader than long. The abdomen is relatively small and is folded under the thorax, lying in a groove which it fits so perfectly as to be quite hidden from above. The appendages of the abdomen are much reduced in number. The male has two pairs; the female has four pairs, which it uses for carrying its eggs. The first pair of walking-legs are comparatively large, and end in chelæ, or pinching-claws. The other eight legs terminate in simple points, except in the swimming varieties, when the fifth pair is flattened to form fins, or swimming-paddles. The eye-stalks are long and fit into sockets on the carapace. Both pairs of feelers are small. The antennules are frequently folded into small grooves. The external or third pair of maxillipeds are broad and flat, and cover the mouth-parts like a lid, or operculum. [pg273]

Crabs, like other crustaceans, are scavengers, living on dead animal matter; but the land species are also vegetarian in diet. They are great fighters, but are also wily, often averting danger by resorting to stratagem. They are an interesting and curious group, as they possess a good degree of intelligence and have amusing habits.

From the time they leave the egg until they attain the adult form they pass through several complete and singular metamorphoses. The most marked forms are called the Zoëa and the Megalops. So little do these resemble the adult that originally they were classed as distinct genera far removed from the one to which they really belong. After the larva has moulted several times it appears as in the illustration on page 248—the last zoëa stage. From this it changes directly to Megalops; the Zoëa, seeming to be attacked with violent convulsions, wriggles out of its skin a full Megalops (page 248). The animal then has enormous eyes, an extended abdomen, an elongated carapace, and swimming-legs. This stage is a short one, and at the first moulting changes to a form nearly approaching the adult. From this time they grow by shedding the shell at certain periods. This shedding is supposed to occur twice each summer until they have reached full growth, after which it is probable that they do not again moult; for often they are found with extraneous organisms, such as barnacles and sponges, upon them, of a size that must have required a considerable period of time for growth. The sexes of the same species sometimes differ so much that it is difficult to classify them. Even naturalists have been led into the error of assigning the male and female to separate species.

The front side margins of the carapace in many crabs are edged with a row of teeth or with spines, which vary in number and character in different species. In the spider-crabs the whole surface of the carapace is generally studded with tubercles, spines, and stiff hairs of a peculiar character. This armature is for protective purposes, and is often used to secure foreign bodies, such as algæ, hydroids, and polyzoans, which the crabs place upon their backs to disguise themselves. The burrowing crabs are usually smooth. When in motion the crab moves sideways, using the legs [pg274] of one side to pull with and those of the other side to push with. As all the legs do not move at the same time, a continuous and uniform motion is kept up. Some species move with great rapidity, notably the sand-crab, Ocypoda arenaria. Often when pursued they will run into the surf instead of to their holes. The common edible crab, Callinectes sapidus, of the Atlantic coast, the fiddler-crabs, and the spider-crabs are among the well-known representatives of Brachyura.

The members of this family are known as "spider-crabs." Their bodies are thick and more or less round in form, narrowing in front to a long, beak-like projection. The surface is generally rough and irregular, having tubercles, spines, prickles, and hairs. The legs are long. These crabs are often covered with seaweeds, hydroids, and other organisms, which they gather with their long and flexible chelipeds and place upon their backs, presumably to conceal themselves from their enemies. They seem to select, instinctively or with reason, such things as will bear transplanting, sometimes using sponges and polyps which are not destroyed by being torn apart, and they also select their dress with reference to its masking uses. A Hyas covered with bright-colored algæ was seen to remove them and replace them with sponges, when transferred to the locality of the latter, where the former did not grow. The animal takes in his claw the object he has gathered, and first holds it to his mouth, where it is moistened with a secretion of mucus or cement, and then places it on his back. If it does not hold, the operation is repeated, often several times, a new spot on the shell being selected each time. It has also been found that the coats of these crabs are covered with hairs which are differently arranged in different genera, some being hooked, others serrated, etc., and that these aid in holding the transplanted organisms in place. The crab is sometimes so covered with these growths as to be entirely concealed beneath them. It is a sluggish animal, and inhabits shallow water along the whole of the Atlantic and Pacific coasts.

The Amphipoda have a laterally compressed body, with gills on the thoracic feet and an elongated abdomen. The segments of the thorax are not united, nor covered by a carapace, but the whole body is covered with a segmented, polished, flexible cuticle. The three anterior legs of the abdomen are for swimming-feet, and the posterior ones are adapted for springing. The antennæ are long and hairy. The amphipods comprise the beach-fleas and many other small crustaceans which abound between tide-marks on all beaches. Besides serving in no small measure as food for fishes, they are scavengers of the beach, and consume large quantities of waste matter. They are sometimes used in preparing skeletons for anatomical specimens. Animals to be skeletonized, being fastened to boards and anchored just below the surface of the water in sheltered places, are divested of all flesh in a few hours, and the bones are more completely cleaned than if prepared by a naturalist.

The isopods have an elongate, flattened, but more or less arched body, composed of seven thoracic segments and a short abdomen of six segments. The six segments of the abdomen are smaller than those of the thorax, and are often more or less united, sometimes into a single piece with scarcely any trace of division above; but the number of pairs of appendages is generally six, showing the composite nature of the apparently simple organ. The last segment, or telson, is broad and has a pair of modified appendages. The seven thoracic legs are not all equal, as the name would imply, but vary greatly in different species. As a rule, they are adapted to walking or attachment, and in the female some have delicate plates which form brood-pouches. The swimming-feet fold under the abdomen, and in some species are inclosed by the first pair, which are large and plate-like, and form a complete cover for the others. The isopods are a large and widely distributed order, varying in size, and are inconspicuous because they cling closely to objects. They are retiring in habit, though extremely ferocious.

The sow-bugs or pill-bugs, common in gardens, under leaves in the woods, and under almost any pile of rubbish among decaying vegetable matter, are a land species of isopods. Other species inhabit [pg292] ponds and streams of fresh water, and still others are found along the shores of all oceans, abounding among the marine vegetation of the shallow waters. Some swim free in the open sea; others are brought up from the greatest depths. Others, again, are parasites, and live in the internal organs of fishes and prawns. Sometimes a prawn is found having what appears like a very swollen throat, which actually is a little parasitic isopod of the family Bopyridæ attached to its gills.

CLASS MERISTOMES

CLASS PANTOPODA (Lang)

This order of animals, like Limulus, has no definitely determined position in the classification of marine organisms. About one hundred and fifty species of Pycnogonida have been described, of which thirty are found on our coast and are commonly known as sea-spiders. They are found crawling slowly over seaweeds, hydroids, and sponges, and appear to be all legs, but, like other animals, have a digestive, a circulatory, and a nervous system. They are devoid of organs of respiration. The body has a cephalothorax, which bears a conical suctorial proboscis on the anterior end, and on top a prominence containing four eyes. It has three pairs of appendages, two pairs of which are sometimes lacking; then come three free segments and a rudimentary abdomen. There is a pair of short appendages bearing claws (chelæ) and four pairs of long walking-legs. The walking-legs contain a tubular outgrowth of the body, into which the stomach extends. The egg-sacs are in the legs, and open at the basal joints. The male is provided with an extra pair of legs, for the purpose of carrying the eggs after they are deposited by the female. The [pg297] ovigerous legs are run through sac-like pockets and bent under the body, and thus the eggs are carried until hatched.

TERMS USED IN DESCRIBING MOLLUSKS

Branchiæ: Gills, or breathing-organs; organs subservient to respiration through water. Same as ctenidia.

Buccal mass: The mouth-parts as a whole; the organ of prehension and mastication of food; the pharynx: present in all mollusks except lamellibranchs.

Columella: An upright pillar in the center of most of the univalve shells, round which the whorls are convoluted.

Crenulated: Having a series of notches; marked as with notches, as the indented margin of a shell.

Crystalline style: A transparent gelatinous substance of unknown function, which fills, at times, the stomach-parts of certain mollusks.

Ctenidia, plural of Ctenidium: Gills, or breathing-organs, adapted to water-respiration. [pg303]

Dextral: Having the aperture on the right side of the shell when the apex is upward.

Lingual ribbon: The chitinous band of teeth, or rasp, borne upon the odontophore; the radula.

Mantle: A fleshy or membranous outgrowth of the outer body-wall; also called pallium.

Nephridium: The renal organ of mollusks, corresponding to kidneys in vertebrates.

Oper´culum: A horny or shelly plate which serves to close the aperture of the shell when the animal is retracted.

Otocyst: The cavity, or cyst, which contains the essential parts of an organ of hearing.

Pallial line: The impression or mark made by the mantle, or pallium, on the inner surface of a bivalve shell.

Per´istome: In zoölogy, mouth-parts in general; in conchology, the margin of the aperture of the shell. [pg304]

Reticulated: Having distinct lines or veins crossing like a network; covered with netted lines.

Sculpture: Elevated or impressed marks on the surface; markings resulting from irregularity of surface; tracery.

Sinistral: Having the aperture of the shell at the left; opposite of dextral.

Suture: The line of junction of the successive whorls of a univalve shell, or the line of closure of the opposite valves of a bivalve shell.

Testaceous: Having a hard shell, as distinguished from crustaceous, or soft-shelled.

Umbilicus: A central, navel-like depression in the body-whorl; a circular, more or less central pit or hollow.

Umbo: The beak of a bivalve shell; the protuberance of each valve above the hinge.

Varices, plural of Varix: Raised marks on the shell denoting a former position of the lip of the aperture, and indicating periods of rest.

MOLLUSKS

We now come to another large and important group of animals, with characters so peculiar to itself and differing so radically from those which distinguish any other class of living creatures, that it may be said to occupy almost a unique position in the animal kingdom. Recent investigations have demonstrated that the larval form of mollusks presents some remarkable points of similarity to the embryonic forms of the Annelida and to the larvæ of some other classes of lower organisms. This discovery is one of the triumphs of embryology in its patient search for that connecting-thread that weaves together all the varying forms of animal life. Aside from these subtle evidences of relationship revealed by the microscope, the mollusks appear to occupy a position of considerable isolation in the biological world.

As accepted by zoölogists to-day, this phylum is but the remnant of its former self. Aristotle considered all creatures with a testaceous covering to belong to a single family, and those later patriarchs of biology, Linnæus, Cuvier, and Lamarck, extended the group to include the greater part of all the marine invertebrate animals. Little by little the phylum has been shorn of orders and classes. First, the worms and the Echinodermata were separated into distinct phyla; then the barnacles were discovered to be crustaceans, and were accordingly removed from their position as "multivalves" under the Mollusca; then the tunicates, or ascidians, were found, through the critical examination of their larval stage, to be merely masquerading as mollusks; and lastly, the brachiopods have been somewhat reluctantly removed from their old position with the mollusks and given the [pg306] distinction of a phylum almost exclusively to themselves: they retain their old associations only in the name of Molluscoida.

With some exceptions, all mollusks secrete from their outer skin, or mantle fold, a calcareous protective covering, or shell. This may be either "univalve" or "bivalve" according as it consists of one or two pieces. This phylum includes all the sea-shells which are so commonly found along every ocean beach, in the tide-pools, on rocks at low tide, in estuaries, and, indeed, wherever sea-water is present. The phylum also includes, as one of its large suborders, all the snails and slugs that are to be found crawling upon the land. These are true mollusks, which differ essentially from their marine brethren only in that they breathe by means of a pulmonary sac or lung instead of by gills. There are also many genera and species of mollusks that find their habitat only in the fresh water of rivers, lakes, or ponds; curiously enough, many of these fresh-water forms, like the purely terrestrial snails and slugs, are air-breathers, possessing no gills whatever, and are consequently obliged to make periodic visits to the surface of the water to obtain their necessary supply of oxygen. There are also numerous forms of mollusks that are entirely deprived of a shell covering; and, again, there are intermediate types between these two extremes that produce only more or less developed rudimentary shells. Notwithstanding these variations in the matter of a shell covering,—an important consideration in this phylum,—by reason of their anatomical features these "naked" forms are mollusks quite as much as are those that secrete the most highly developed tests.

The marvelous beauty of sea-shells and tropical land-shells, their almost infinite variety in form and coloring, has given to them an interest among collectors that is very great. There are many wonderful conchological collections in public museums and in private cabinets. It would well repay the lover of beauty as well as the more serious student of nature to examine carefully such collections when opportunity offers, for nowhere in the realm of nature can more exquisite coloring and modeling be found. The fact that shells may be preserved for all time without the expense and the vexations of preservative fluids has no doubt induced many [pg307] to choose this field of natural history for special study. But the true student of zoölogy does not confine his investigations in this phylum to considerations of the shell only, for the protective armor constitutes only a portion, although an important portion, of the anatomy of the mollusk. On the same principle, it would hardly suffice to examine only the skeleton of vertebrate animals in order to become acquainted with the fishes or mammals. In a sense, the testaceous covering of a mollusk may be likened to an outer skeleton.

The older zoölogists were inclined to ignore almost entirely the animal or "soft parts" of mollusks, and their classification of the phylum into "univalve," "bivalve," and "multivalve," based upon shell-characters alone, has since been proved to be wholly artificial. The terms "univalve" and "bivalve" are, of course, often and correctly used to-day to designate mollusks possessing a single or a double shell, such as the common garden-snail, which carries upon its back a single spiral shell, and, on the other hand, the oyster or clam, which is inclosed within two valves which fit closely together. But these terms are not technically used, although they do indicate in a general way the more modern classification. Even among some comparatively recent conchologists a tendency to belittle the value of the "slimy creature" within the shell has led to some curious errors of grouping—mistakes which more thorough and scientific investigation has brought to light. In general, the higher classification into classes, orders, suborders, and families is exclusively based upon anatomical features, and to a large extent, also, is that of the genera; but species are always determined by their shell or conchological characteristics.

When a certain familiarity with the forms and general appearance of shells is gained, a glance at the shell alone will almost always suffice to place it at once in its true generic position, for, along with modifications of the animal itself, corresponding modifications of the shell are quite certain to take place. Hence a fairly expert zoölogist should be able to determine with considerable accuracy from an empty and dead shell the anatomical features of the animal that at one time inhabited it. [pg308]

One of the main reasons for the special interest that seems to have attached to the study of conchology is derived from the fact that the durability of shells has caused their almost perfect preservation as fossils from the very earliest periods of geological time, thus furnishing the key to the solution of many problems of evolution. Upon this page of the earth's history the letters are sharp and clear, and geologists possessing a knowledge of recent forms of mollusks as well as of their geographical distribution have been enabled to read some wonderful stories of the cosmic history of islands and continents.

GEOGRAPHICAL DISTRIBUTION

Mollusks are found in every part of the world. The arctic seas possess their own characteristic faunæ, the more temperate waters of Europe and of America contain their own peculiar genera and species, and the warm waters of the tropic seas furnish the conditions favorable to the life of an immense number of characteristic forms. Again, there are the littoral species, that live only between tide-marks and are therefore exposed to the air for a number of hours each day; some of these live just about high-tide mark and have become almost terrestrial in their habits, while others must be sought at the point of lowest tide, where for only a short time each day they are deprived of their natural element. Then there are the shallow-water forms, which never appear above low-tide mark save when a neap tide surprises them; their range in depth extends to about the hundred-fathom line, more or less. Beyond this depth to several hundred fathoms other characteristic forms appear, and from the more profound depths of mid-ocean the dredge has brought to light a host of curious and interesting species.

It is the temperature of the water rather than the depth that appears to influence the distribution of marine mollusks. Thus, certain species whose natural home is in the shallow waters of the Arctic Ocean have been taken in very deep waters off the southern coast of the United States, the temperature conditions in both stations being substantially the same. This fact, however, must not be too freely accepted as establishing a principle. Some [pg309] shallow-water forms have been taken at great depths, but in general the abyssal fauna is a peculiar one that cannot well be marked off into geographical provinces.

THE ARCTIC PROVINCE

The east coast of America is divided into several molluscan faunal regions. A series of very-cold-water forms belonging to a circumpolar region, called the "arctic province," are found as far south as Newfoundland. On the New England coast a number of these arctic species are also found, urged south by the influence of the cold Labrador current. The most characteristic genera belonging to this arctic fauna which are found upon the Maine and Massachusetts coasts are Buccinum, Chrysodomus, Sipho, Trophon, Bela, Velutina, Trichotropis, Lacuna, Margarita, Pecten, Leda, Yoldia, Astarte, and Mya. Examples of all these genera are encountered as far south as Cape Cod.

THE BOREAL PROVINCE

A "boreal province" corresponds with a similar faunal region upon the European shore. The mollusks which compose this fauna are about three hundred in number, and range along the New England coast from the Gulf of St. Lawrence to Cape Cod. It is a somewhat remarkable fact that many of these species are identical with English and French forms. The striking genera upon the American side are Purpura, Littorina, Polynices (Lunatia and Neverita), Acmæa, Margarita, Chiton, Doris, Æolis, Mytilus, Modiola, Thracia, and Nucula.

THE TRANSATLANTIC PROVINCE

Cape Cod has been regarded, until very recently, as a sharp divisional point between the boreal and the transatlantic provinces, the latter faunal area extending down the Atlantic coast of the United States to southern Florida. At Cape Cod the Labrador current is deflected from the coast, and the warmer shore waters south of that point are unfitted for the development of the boreal forms, though some of them, as we shall see, have passed the [pg310] barrier and maintain themselves very successfully at Martha's Vineyard and in Long Island Sound. Some of the species whose natural habitat is south of Cape Cod are also to be found north of that point, but they do not reach their full development in the colder waters of Massachusetts Bay.

The long stretch of coast-line from Cape Cod to Florida is easily susceptible of faunal subdivision at Hatteras, below which locality a decided mixture of Antillean species is apparent. Between Long Island Sound and Hatteras the littoral molluscan fauna is disappointing to the collector, for the number of species is relatively small, and few even of these are entitled to any claims to beauty of shell. The nature of this coast, virtually a great sweep of exposed sand-beach, is not conducive to a varied or rich fauna. But if this portion of the transatlantic province is lacking in interest to the shell-collector, it is anything but disappointing to the army of men employed in the oyster- and clam-fishery. It is only within this faunal area that the American oyster, Ostrea virginica, the best of the edible shell-fish, finds its natural home, and here the oyster-culture is most extensively carried on.

After storms the Jersey beaches are frequently strewn with Mactra, Tagelus, Arca, and Ensis; in more sheltered places Fulgur and Polynices (Lunatia) are commonly met. These may be accepted as the most characteristic genera of this province.

Just south of Cape Hatteras an observer is struck with the sudden change in the appearance of the shells on the beach. Cardium, Cassis, Dolium, Arca, and Cancellaria at once suggest the West Indies. About the vicinity of Hatteras the Gulf Stream approaches very near the land, bringing with its warm waters many wanderers from tropical homes. From Beaufort to Florida there is another long stretch of exposed and shifting sand-beach, which offers a scant return to the collector of mollusks.

THE CARIBBEAN PROVINCE

When Florida is reached a new world is opened to the naturalist, for there a better acquaintance is made with the great Caribbean province, which, extending from Florida to the northern shores of South America, embraces all the Bahamas, the West [pg311] Indies, the Gulf of Mexico, and the coast of Central America. Strangely enough, the mollusks of the west coast of Florida are more nearly related to those of the transatlantic province than are the shells of the east Florida coast. This remarkable fact in geographical distribution can only be explained by assuming that an open waterway once existed across the northern part of the Florida peninsula, connecting the Atlantic and the Gulf, through which a mingling of the shallow-water forms from Georgia, the Carolinas, West Florida, and the Gulf coast took place. Thus it would appear that when Florida was an island the fauna of its east coast, originally largely Antillean, was less disturbed by the southern migration of American species. The Florida Keys are essentially Antillean. The Caribbean or Antillean fauna is an exceedingly rich and varied one. Among the most prominent genera which may be encountered upon the Florida coast are Strombus, Fasciolaria, Oliva, Marginella, Natica, Sigaretus, Littorina, Tectarius, Neritina, Melongena, Cardium, Callista, Tellina, Lucina, and Cyrena. In such an extensive and rich faunal province one must not expect to find in any given locality a representation of all the characteristic genera. For instance, collections made at Havana, at Nassau, and at Vera Cruz would each contain forms more or less peculiar and local, but certain species would be found in each collection.

On the west coast of America quite the same faunal division into more or less well-marked provinces is to be found. Bering Sea belongs to the arctic province, and contains, with Labrador and Greenland, many identical forms.

THE ALEUTIAN PROVINCE

The shore waters from the southern peninsula of Alaska down to about Vancouver comprise the Aleutian province. Within this area occur some arctic species, notably the soft-shell clam, Mya arenaria, which the fishermen gather in such large quantities for bait along the Maine coast. An increasing number of species common to this west-coast faunal region and to the boreal province of the east coast are being recorded. Some of [pg312] these have been introduced from the East by the agency of man, but others no doubt have a natural range through the icy waters north of America and down through the Bering Sea into the Pacific.

THE CALIFORNIAN PROVINCE

The Californian province extends from the neighborhood of Vancouver to Cape St. Lucas and has about five hundred species. The northern portion of this area contains some very characteristic forms, together with a good mixture of species of more northern habitat; it might properly be regarded as a subprovince. From San Diego south to the cape the character of the fauna gradually changes; this coast-line of southern California has also been considered a subregion. The main characteristic of the Californian province is a large development of Haliotis, of the patelliform mollusks, and of the chitons. A very few minutes on any good collecting-beach of California would convince the Eastern conchologist that he had entered upon an entirely new field of research. The most notable genera are Calliostoma, Chlorostoma, Scurria, Acmæa, various genera of the Chitonidæ, Purpura, Monoceras, Amphissa, Norrisia, Olivella, Chorus, and Haliotis.

THE PANAMIC PROVINCE

The warmer waters of the Gulf of California belong to the Panamic province, which extends down to South America. This is one of the richest and most interesting faunas in the world. At Panama alone, Mr. C. B. Adams, a noted collector and student of conchology, took upward of four hundred species. About eight hundred species are known in the Gulf of California alone.

It must be borne in mind that these faunal provinces relate to littoral and shallow-water species, for the present knowledge of deep-water forms is not sufficient to permit of generalization upon their distribution.

We review here only the conspicuous forms along our own coasts. It may be well to note, however, that in some other parts of the world the development of molluscan life is far [pg313] in excess of anything to be found upon our shores. The veritable paradise of the naturalist is the East Indies. There the "aristocratic" genera, so called on account of their marvelous beauty, occur in their highest development—Voluta, Mitra, Oliva, Conus, and the various murices. There also are to be found the pearl-oysters, Meleagrina margaritifera, that yield their valuable harvest, and the giant clam, Tridacna gigas, which measures sometimes five feet in length. Over eight thousand species of mollusks are described from this surpassingly rich region, yet this vast province, as compared with the American and European shores, has been but superficially exploited by the naturalist. In whatever part of the world a naturalist may find himself, there is always a tempting array of molluscan life to attract him. Each fauna possesses features peculiar to itself, and from the point of view of the true naturalist, the more somber-hued and conventionally formed mollusks of Northern shores are no less interesting than the gorgeously tinted and fantastically shaped species of the tropics. From any faunal province of our own country one may readily gather all forms necessary to furnish ample material for study from which one may acquire an excellent idea of the biological features of the entire phylum.

STATION AND HABITS OF THE MOLLUSCA

The word "station" is used to indicate the nature of the surroundings which an animal chooses as most suited to his well-being. Some groups of mollusks, like the littorinas, the trochids, the purpuras, and the majority of those having patelliform shells, generally live on rocks above low-tide mark; other genera, like Buccinum, Sipho, and Chrysodomus, prefer rocky or gravelly ground below low-tide mark. Other mollusks burrow deep in the mud, many prefer sandy bottoms, while a host of other species seek homes upon the tangled masses of seaweed, living like arboreal creatures in the submarine forests. Nearly every conceivable character of sea-bottom or shore-line between tides harbors its own peculiar types of molluscan life. There are some very curious genera of bivalves that bore their way into the hardest rock and [pg314] there find a comfortable shelter for life. A numerous class of pelagic or free-swimming mollusks supposedly never go to the bottom at all, but spend the whole of their existence on or near the surface of the sea, always in open water, where their fragile shells may not be injured by rough contact with solid substances.

The food of some is vegetable, of others, animal. The bivalves, like the clams, oysters, cockles, and mussels, feed only on microscopic organisms. They create a current of water through their siphons, or mantle openings, and then, by a process best known to themselves, catch and swallow all the animalculæ thus brought to their mouths. The univalves which possess a siphon are, for the most part, carnivorous, and are often most voracious creatures. They feed upon any animal matter they can find, while some of them are enabled by means of a sharply toothed tongue to bore through the solid shells of other mollusks and extract the succulent vitals from within. One energetic little mollusk in particular, Urosalpinx cinerea, is for this reason a great pest upon the oyster-beds. Univalves not possessed of a siphon may generally be considered herbivorous; they pass most of their time peacefully browsing upon algæ.

Mollusks are all oviparous or ovoviviparous; that is, they lay eggs, or, laying eggs, they retain them within their shells until the young are hatched out. As a rule, each species of mollusk has its own particular method of protecting its eggs from external injury. Some construct tough, leathery capsules which are strung together in various patterns. The egg-capsules of Purpura lapillus, resembling little pinkish or yellowish club-shaped stalks, may frequently be found in the crevices of rocks and under the rockweeds. The egg-cases of Polynices (Lunatia) are most peculiar, resembling inverted gelatine-bowls with the bottom knocked out; when wet they are semi-elastic translucent masses in which may be seen myriads of eggs. Buccinum undatum arranges its hemispherical egg-capsules in layers one above the other. The number of eggs so deposited is often very great, running well into the thousands. Egg-capsules of Fulgur are leathery coils of angular disks adhering by one edge to a connecting-band of a similar texture. (See Plate I.) [pg315]

In bivalves the eggs are retained within the parent shell until hatched, and the young, which then escape into the water, are very different-looking creatures from the parent. Generally the young bivalve is free-swimming and exceedingly lively in its movements; sometimes by means of cilia it is enabled to attach itself to any passing host, and thus the species is widely disseminated. The fry soon lose their embryonic form and take on the characteristics of the adult.

The longevity of mollusks varies greatly with the species. Some attain an age of from ten to fifteen years, while some are only annuals. Oysters continue to grow for four or five years, after which they may survive many years more. In truth, little is known concerning the duration of life even of our better-known shore species.

In point of intelligence, mollusks must be relegated to a very low position. They give evidence of possessing no more than the most primary instincts, those of self-preservation and of reproduction. There are some forms that exercise a high degree of protective mimicry. The highest class of mollusks, the Cephalopoda (cuttlefishes, octopi, etc.), is widely separated from the other classes in the development of faculties that appear to correspond with intelligence. They are exceedingly crafty in the pursuit of their prey as well as in eluding capture.

STRUCTURE OF MOLLUSKS

Among the invertebrate animals, especially in the lower orders, wide physiological departures from central or typical forms are frequent. It often happens that a whole group or even suborder will differ so materially in its general characteristics from another group or suborder belonging to the same phylum that the student will be puzzled at first to understand how the two can be nearly related. In many such cases it is only when the essential features of the phylum are thoroughly understood that the relationships of its suborders can be appreciated. An example of widely divergent groups within the same phylum has already been shown in the Echinodermata. Who would at first suppose that the graceful Astrophyton could bear kinship to the inert [pg316] holothurian, or that both of these have the closest family ties with the sea-urchins?

The probable reason for these startling departures from a typical form is that in the lower orders of life, where the organs and their functions are comparatively simple, the laws of evolution operate far more quickly in the adaptation of an organism to environment and changed conditions of life. A decided tendency to this departure from the type is a feature of the mollusks. It would be difficult, if not impossible, to give a general description that would fit both a common garden-snail and the common oyster, yet both are mollusks. A concise definition of the phylum is therefore practically impossible, and it seems here as if nature resented all attempts to circumscribe her living forms by rigid rules.

The most persistent characteristic of the Mollusca is the possession of the "mantle," a sort of outer skin which, like a bag or sack, envelops the creature above and about the sides, but is open below, permitting the animal at will to protrude or withdraw its foot. From the outer surface of this sheath-like mantle, or fold, a calcareous shell is secreted. The modifications of this mantle are infinite; indeed, in some well-marked groups it seems to have wholly disappeared, having in reality become fused to the sides of the animal, and having become therefore a mere outer skin, and no longer a tunic or cloak, as originally intended. As already noted, the mantle does not always secrete a shell, a fact which again reminds us that we cannot give a good comprehensive description of the phylum that always holds true throughout its subdivisions. The best that can be done is to give in general terms the characters which appear in a majority of the forms. A convenient method of going about this is to create, for the sake of clearness, an ideal, model, or fanciful mollusk and clothe it with all the most salient molluscan features, and from such a basis to develop, as we go on, the various types of the actual orders and suborders. There is one class of mollusks, the Amphineura, which conforms reasonably well in most of its features to our comprehension of the schematic mollusk. This class is sometimes referred to by biologists as the "primitive" or "original" mollusks, from which all the other classes have since been derived; but the [pg317] evolutionary history of the development of the various molluscan orders through geological time does not seem to bear out the fact that an "ideal" mollusk, as we shall construct him, ever actually existed, or that his prototype, the Amphineura, was the first and consequently the ancestral type of the phylum. We must therefore only accept this ideal mollusk theoretically, to serve as a guide for the time being. We may profitably use it only as a lay figure—a sort of manikin, which will introduce us to the phylum. After our introduction we must forget our imaginary type and abandon any notion we may have conceived of the parental position of the Amphineura, its closest imitator in actual life.

THE IDEAL MOLLUSK

The ideal mollusk has a compact, somewhat elongated body, the under or ventral portion of which is thickened into a muscular disk, upon which it creeps along. This disk is called the foot. (Note a snail thus crawling upon his "foot.") The foot is rounded or obtusely pointed posteriorly. Forward, the body is slightly narrowed into a neck, and then expanded again into a head. Upon this head are carried two projecting, mobile, fleshy tentacles, one upon each side, that superficially resemble two horns. At the base of each tentacle, upon the inner side, is an eye. Just below and between the tentacles is a small horizontal slit,—the mouth,—the lips being slightly thickened. The visceral portion of the animal is above the foot, or dorsal to it, and extends the whole length of the animal from the mouth to the excretory opening, the latter being situated posteriorly. The visceral cavity is inclosed above by a thin skin; indeed, it is but the great thickening of this skin below that constitutes the foot.

The digestive tract, beginning at the mouth, opens immediately into a muscular throat, which is called the buccal mass. Within the buccal mass there is a long, fleshy ribbon that bears upon its upper surface numerous rows of sharp teeth; these rows of teeth run crossways on the ribbon, each row containing more or less prominent median teeth, with several laterals upon each side, and with marginal teeth on each side of the laterals. This is called the radula, and is used for tearing or rasping the food. When [pg319] not in use it lies coiled up within the buccal mass. Beyond the buccal mass, food passes into the esophagus, which widens out into a muscular pouch or stomach; this may also be provided with chitinous teeth or hard knobs or plates for the purpose of further triturating the food. Above and partially surrounding the stomach is a large reddish or brownish liver, which furnishes to the alimentary canal the digestive juices. From the stomach the intestine leads to the terminal anal opening. There are two organs, serving the function of kidneys, placed dorsally one upon each side of the body (nephridia). A heart lies within the median line of the body, and consists of a ventricle and two lateral auricles. The vascular system is almost entirely closed; only in so far as it is partially open does it essentially differ from that of higher groups; the blood is whitish or light bluish, and receives its oxygenation in the gills or along the free mantle surface, through which it courses in exceedingly thin capillaries. In this manner respiration is carried on to some extent throughout the whole outer surface of the body. There are two branchiæ (gills). These have the appearance of small feathers and are placed upon each side of the animal posteriorly; they project slightly. Spread over the top of this animal, fitting it perfectly, is a thin fleshy covering attached to its dorsal portion like a skin, but hanging free, like a flap, over the sides, the head, and the posterior end of the animal. Upon the sides it may just cover the tips of the branchiæ, but in front the head is seen to project from under it. The loose-hanging portion of this sac-like covering is somewhat thickened, and perhaps recurved upward upon itself. Upon the edge of this flap all the way around may occur a row of cilia, or tentacular processes. This cloak-like covering is called the mantle, and, as already noted, is the most peculiar and persistent characteristic of the Mollusca. The "cavity" formed between the loose-hanging portion of the mantle and the sides of the foot is called the mantle cavity, and contains posteriorly the gills, or branchiæ. From the outer surface of this mantle a calcareous secretion takes place, forming a shell, which, in our ideal mollusk, will be shaped in conformity with the surface outlines of the mantle, oblong and convex above. Over the lower portion of the shell the edge of [pg320] the mantle recurves. When the creature is disturbed or is at complete rest it may withdraw that portion of the mantle which protrudes from below the shell entirely within the edge of the shell, so that the "soft parts" may be wholly covered, and thus protected from harm. In such a state of rest nothing may be seen from above but a shell. The entire upper surface of the mantle is firmly attached to the under or inner side of the shell, except the mantle margin, this being free.

The nervous system consists of a circumesophageal ring of nerve-cells, with two cords passing along the digestive tract to the posterior end of the animal. In the head and above the buccal mass are several series of nerve-ganglia. These also communicate with the posterior portion of the animal through two parallel cords which pass along its ventral side. From these four principal branches, which traverse the entire length of the creature, minor nerve-cords are thrown off to the tentacles, the foot, the branchiæ, and the various organs of the viscera. The sexes are separate.

Reviewing our "typical mollusk," we find that it is bilaterally symmetrical—that is, uniform upon both sides of a median line from mouth to excretory opening; is unsegmented; has the ventral surface thickened into a creeping foot or disk; and is possessed of a head with tentacular processes, a radula, lateral branchiæ, a heart with a ventricle and two auricles, a well-developed mantle, and a shell.

If the reader can learn these few details of organization he knows the structure of a mollusk. In turning to the actual living forms he will find merely modifications (though sometimes confusing ones) of these various parts.

CLASSIFICATION

The Mollusca are divided into five great classes: Amphineura, Gasteropoda, Scaphopoda, Pelecypoda, and Cephalopoda. These names, it will be noticed, with the exception of the first, all refer to the foot, the modifications of the foot being selected as the basis of the first great divisions of the phylum. The Gasteropoda crawl upon the thickened ventral surface of their bodies (already [pg321] referred to as the foot), as the common garden-snail, the periwinkles, and in general all those mollusks which have a spirally coiled shell. The Scaphopoda have a long, worm-like foot, with which they burrow in the sand or mud. Their shells are like miniature elephant-tusks, but are open at both ends. The Pelecypoda have a more or less club-shaped foot, utilized, in the many families, for a great variety of purposes. They are always inclosed in a bivalve shell. Familiar examples are the oysters, the clams, mussels, etc. The Cephalopoda have the foot modified into a number of arms, which encircle the head or the mouth. They are the cuttlefishes, the octopi, squids, etc.

CLASS AMPHINEURA

ORDER POLYPLACOPHORA

The Amphineura, as already observed, approach most closely to the ideal mollusk just described. They are bilaterally symmetrical. This fact is so important that it constitutes them a class, notwithstanding the fact that in respect to the foot (the basis of division into classes) they would be included with the Gasteropoda, for (barring some exceptional instances) they creep along upon a foot quite as our ideal mollusk would, and as the Gasteropoda do. The head carries no tentacles, thus essentially differing in this respect from the ideal form. The mantle is extended down in front, completely covering the head. The branchiæ are confined to a few pairs of ctenidia, or plume-like gills, within the mantle groove or cavity, and are arranged upon each side of the excretory opening like small feathers.

There are two orders of the Amphineura, the Polyplacophora and the Aplacophora (or Solenogastres), the one name meaning "bearing many plates," and the other "without plates," the word "plate" in this sense being synonymous with "shell." The shell of the first order consists of eight calcareous disks arranged in a longitudinal row along the back or dorsal side of the animal, which overlap like shingles on a roof and admit of great variation of form in the various families. [pg322]

It will be observed from the examples given that the shell plates do not entirely cover the mantle, but that a considerable portion of the upper mantle surface is left exposed along the side of the animal. This exposed portion of the mantle is called the girdle. It is always very much thickened and is often exceedingly tough. In some species it is covered by a great number of calcareous spicules or granules which are embedded in the leathery mantle tissue. Strangely enough, the Chitonidæ (a large family of the Polyplacophora) possess a great number of eyes scattered over the shell plates like minute dots.

The members of this order are to be found in all parts of the world, but their greatest development is upon the west coast of America. In California the student of marine life has a splendid opportunity to examine the chitons. They are generally to be found adhering to the under surface of stones about low-tide mark. They are very sluggish in their movements and may readily be removed from their resting-places by suddenly thrusting a knife-blade under the foot and prying them off. When thus detached they have a habit of rolling up into a ball and so remaining indefinitely; to prevent this they should be placed at once in a jar of sea-water, where they will resume their natural position. For preservation as cabinet specimens, chitons should be tied down between two boards or flat substances, to hold them firmly extended until dried; otherwise they are apt to contract out of shape.

Six or eight species are exceedingly common upon the west [pg323] coast. The collector who has successfully taken a number of these will not fail to note the varying degrees of width of the girdle in the different species. In some cases the girdle partially covers the overlapping shell plates. The largest of all the chitons inhabits the California shores and is known as Cryptochiton stelleri. It measures fully six inches in length and three in width. In Cryptochiton the girdle is continued over the shell plates as a tough, gritty, brownish covering. The shell plates are white, and, as detached pieces, are frequently to be found cast up upon the California beaches, where, from their curious shape, they are often referred to as "butterfly-shells."

On the east coast of America there are comparatively few species, and these are all small and inconspicuous. The three commonest ones are Chiton ruber, C. albus, and C. apiculatus. They may readily be found on stones or dead shells fished up from below low-tide mark, or in rock-pools left by the receding tide.

ORDER APLACOPHORA

This second order of the Amphineura is entirely destitute of the shell plates characteristic of the first. The outer mantle surface, however, develops a number of calcareous granules which correspond to a shell. The Aplacophora are symmetrical, having the mouth and the excretory opening at the anterior and posterior ends respectively. The foot is greatly modified, being narrowed at times to a mere slit along the ventral surface. Some of them have long, worm-like bodies. This is no doubt a very primitive form of mollusk, or, if not a primitive form, it has greatly degenerated from some higher type. They are supposed to be commensal in habit and live in the deeper water offshore.

The Aplacophora are not littoral animals, and it is extremely unlikely that one will ever encounter them upon the beach, unless, possibly, after the severest of storms. We may therefore leave them with this mere mention and proceed to the second class of mollusks, the Gasteropoda. [pg324]

CLASS GASTEROPODA

The class Gasteropoda is the largest and most comprehensive subdivision of the Mollusca, and within its wide range of families many differing details of organization are to be found. As a class it possesses all the most characteristic features of the phylum, though it is frequently modified in a high degree. This class includes all the univalve mollusks (except Nautilus and Dentalia), such as the snails, the whelks, and the host of spirally coiled land, fresh-water, and marine shells.

The gasteropod foot is, as has been remarked, primarily the same as in our schematic mollusk—a flat, muscular disk caused by the thickening of the ventral body-surface. The neck, head, and tentacles are also quite the same, but considerable modification of these organs will be found when we come to examine some specimens. The mantle is always present, except in the nudibranch or non-shell-bearing forms; but in few of the Gasteropoda is the mantle so regularly simple as in our ideal mollusk.

Perhaps the most striking feature of the Gasteropoda, and one that will at first surprise him who has in mind the simple structure of the ideal mollusk, is the fact that they are always asymmetrical—that is to say, a median line drawn longitudinally through a gasteropod will not divide it into halves of similar anatomical structure.

The quality of symmetry is an important one throughout the lower orders of animal life. In nearly all phyletic or class descriptions the word "symmetry" occurs, and its exact meaning must be understood. Take, for example, a human being; a median line drawn vertically would divide him into two similar halves—upon each side would be an eye, an arm, a leg, etc., of similar shape and construction. So far at least as the external features [pg329] go, man is then a symmetrical creature; likewise the vertebrates in general. Cases of actual symmetry are found in the lobsters and crabs and in the segmented worms. It is usual in describing mollusks broadly and in general terms to call them symmetrical animals, yet here is the largest class within the phylum, whose representatives are none of them symmetrical. In the Gasteropoda the mouth is anteriorly placed in the head, just as in the ideal form, but the digestive tract, after traversing the visceral cavity in the usual fashion, suddenly turns forward and terminates in an excretory opening either on the right or on the left side of the animal, just back of the head. The various other orifices for the genital and renal glands are also placed in this unexpected anterior position. The gills, or branchiæ, are to be found upon one side only, forward of the heart, and differ somewhat in appearance from the plume-like processes of the Amphineura.

What, then, has become of the corresponding gill we should expect to find on the other side? The symmetrical shape of the foot is not in the least altered, but what has happened to cause this distortion of the visceral portion of the animal? And, finally, will this torsion of the body of the snail perhaps account for the spiral nature of the shell?

An evolutionary process is supposed to have taken place in mollusks, which, if real, would no doubt account for these curious conditions of torsion in the Gasteropoda; but the theory upon which this process is based is altogether speculative, and is not fully sustained by the facts in the case. Originally all mollusks are presumed to have been symmetrical, and are assumed to have resembled very much in form the schematic creature we have already described. Now, for some reason, certain of the primitive mollusks, but not all of them, began to develop a larger visceral mass, which, continuing to enlarge throughout many generations, began finally to protrude above and form a hump on the dorsal side of the animal. This hump, containing the liver, a portion of the intestines, and the generative glands, as it increased in bulk became so much elevated that it could no longer maintain itself in an erect position over the body, but, impelled by its own [pg330] weight, began to sag over to one side. Such a process would of course tend to twist the digestive tract and bring the excretory opening constantly farther forward on one side. At the same time, this process would necessarily interfere, by the weight of the overhanging viscera and the shell covering the mass, with the development of the branchiæ lying upon that side and now crowded under the visceral mass. Thus, according to this theory, this process has continued until, in the modern gasteropod, the digestive tract has been bent upon itself and twisted from a straight course into a curve of almost 180°, bringing the excretory opening near or just over the head, where it empties into the mantle cavity; while the original right gill, by the same movement, has been brought to a position on the left side of the head, forward of the heart, the original left gill having been crowded out, eventually to atrophy and disappear. The same torsion is found in the nerve-cords; the heart, situated at about the pivotal position of this twisting process, has turned about upon itself, leaving an auricle in front of the ventricle, one auricle, like one of the gills, having been lost. The mantle portion covering the visceral hump naturally continued to secrete its shell, though always in conformity with the change, the result being the familiar spiral form of the usual gasteropod shell.

This theory may not be satisfactory, but the asymmetry of gasteropods is a problem to be solved, and a more interesting line of biological investigation could not be found.

Let us now take a good example of a gasteropod and locate its various organs; at the same time we may use the occasion to refer to more important modifications of these organs which will be encountered later in the various genera. The most available gasteropod on the east coast of the United States for this purpose, is Fulgur, both on account of its large size and its abundance. Buccinum may be used if the student is north of Cape Cod and therefore unable to secure a good living specimen of Fulgur; the anatomical differences between the two are slight.

Note the siphon protruding forward from a notch in the shell. This consists merely in an elongation of a fold of the mantle, which is held in a manner to constitute a tube, through which [pg331] the animal draws in water to supply the gills, lying just back of the siphon and concealed under the mantle in the cavity already spoken of as the mantle cavity. With the exception of that portion of the mantle which constitutes the siphon, no part of its margin, it will be observed, can be seen, the edge of the shell completely hiding it from view.

In some genera the siphon is exceedingly long—in fact, longer than the body of the animal. In these cases the mollusk is generally fond of burying itself in the sand and maintaining communication with the world above only by means of this long, fleshy tube. In some genera the siphon is protected by an elongation of the shell, as in Fasciolaria (Plate LXXVI.). An extreme example of this is given in the figure on page 343, which represents a species of Murex, where the siphon is not only protected by the shell, but the shell itself is further protected by the double row of sharp spines with which it is beset.

There are some genera which possess no siphons at all, in all of which cases there is no notch in the shell opening, the aperture being round, as in Natica and in Littorina (pages 368, 371). The mollusks of this type make a fold in the forward part of the mantle which serves as a siphon. Such a muscular folding in the mantle would be technically called a functional siphon.

On the posterior dorsal side of the foot is attached a horny plate, of concentric structure about a central or subcentral point or nucleus. This is called the operculum, and serves to close the entrance of the shell when the animal is withdrawn, the object no doubt being protective. The opercula vary to a great extent in the different genera; in some cases they are calcareous, in others cartilaginous. When the aperture of the shell is very large it often happens that the operculum does not entirely close the opening, as in Fulgur, but in Buccinum it is a close fit. The operculum is entirely wanting in the Pulmonata, one of the [pg332] large orders of the Gasteropoda. The figures represent some of the commoner types of opercula.

The opercula have been utilized a great deal in the classification of the Gasteropoda, and especially in some groups that have become terrestrial in habit. Often, when shell-characters utterly fail to give a clue to the proper generic position of a new or rare mollusk, the operculum may be relied upon to indicate it.

TENTACLES

Two tentacles project like fleshy horns from the sides of the head. These are not retractile, as in the land-snails, and their office appears to be that of sensory organs. In both Fulgur and Buccinum the tentacles are comparatively short and stout, and have expanded bases; in many other genera they are long and slender. Almost without exception the Gasteropoda possess tentacles. [pg333]

EYES

In Fulgur the eyes are situated near the bases and upon the outer sides of the tentacles; in Buccinum they are extremely small and are mounted about midway between the bases and the tips of the tentacles. This is the usual position for the eyes in the marine Gasteropoda. Only in the pulmonates, or land-snails, are the eyes placed at the summit of the tentacles. Sight does not appear to be a very important sense in the gasteropods, although the eye in some instances becomes a highly developed organ. A number of forms that have the habit of burrowing deep into the sand or mud are quite destitute of visual organs, and certain cave-dwelling land-shells have entirely lost the sense of vision.

MOUTH AND PROBOSCIS

The mouth will easily be seen in both Fulgur and Buccinum. It is a small slit with slightly thickened, fleshy lips, and is placed on the lower forward portion of the head. In the case of both of these genera the mouth is situated at the end of a proboscis. It will be noted that Fulgur has a comparatively long and stout proboscis, or snout, which is not retractile. Buccinum has a smaller one. It is fairly safe to assume that all gasteropods that possess a proboscis are carnivorous. This organ is greatly developed in some genera, where it actually exceeds in length the rest of the animal. In such instances, no doubt, the creature is enabled to reach the interior portions of the shells of its victims and to devour every vestige of their flesh, for the mouth is most conveniently placed just at the end of this long, trunk-like organ. The genera which have no proboscis are, almost without exception, vegetable feeders.

We must now remove the animal from its shell. It is well to boil it first, for this does away with the annoying mucous secretion that is freely exuded by glands in the foot when the creature is roughly handled. Alcoholic specimens are apt to be much contracted and hardened, and are therefore less satisfactory as subjects for anatomical study. If it is not convenient to boil the [pg334] specimen, break away the shell with a hammer, using care not to lacerate the soft, fleshy portion within; when this is accomplished, wash the animal carefully to remove the slimy exudation. Note the "visceral hump," which is spiral, and which formerly occupied the upper-whorl portion of the shell. The thin skin covering it is the mantle, which below is greatly thickened and free, lying about the foot like a heavy fleshy flap.

MANTLE

The mantle-edge in both of these examples is simple; that is to say, it possesses no fringe of tentacles, nor is it supplemented by extra processes, characters which mark many genera of marine Gasteropoda. In Fulgur and Buccinum the mantle-edge does not protrude below the edge of the shell; but in many genera, especially those which possess smooth, glossy shells, like the cowries (Cypræa) and the graceful Oliva, the mantle is proportionately very much larger. In these two genera, when the animal is extended, as in crawling about the sand, the mantle curves upward and incloses a large portion of the shell itself. Indeed, in some genera the shell is almost entirely concealed by this extension of the mantle (Sigaretus, Natica, etc.).

When the shell is removed, the folding of the mantle which constitutes the siphon can be plainly seen. The office of the siphon has already been referred to, also the fact that the presence of a siphon in the gasteropod mollusk may always be determined by merely glancing at the shell alone, for a notch at the base of the aperture indicates the place through which the siphon passed. In Buccinum this is merely a notch, but in Fulgur the siphonal canal of the shell is much longer. Just why the long siphons of some mollusks should be naked and exposed to danger, while others are so carefully protected by elongated, portions of the shell, is a mystery, but nature is full of such contradictions.

THE GASTEROPOD FOOT

The foot is long, broad, and flat on the under side, like a disk. The variations in the gasteropod foot are almost infinite. [pg335] In some of the species it is amazingly large and powerful, as in Polynices (Natica), and in most of the forms which live along sandy beaches. These are sometimes provided in front with a wedge-shaped process called the propodium, which serves admirably as a plow to push aside the heavy wet sand through which the animal forces its way. In Nassa, which is so common all along our coasts, the foot has two terminal appendages or points behind.

There is no single feature of mollusks more important than the foot, for upon the many modifications of this organ the various molluscan classes are founded. The name Gasteropoda means "stomach-foot," the latter organ being merely a thickening of [pg336] the ventral surface of the animal, giving to the creature, when active, the appearance of crawling upon its stomach.

If a living gasteropod is placed in a jar of sea-water and left undisturbed it will soon crawl up the side of the glass and thus afford an excellent view of the extended under surface of its foot. The majority of the gasteropods are lethargic and slow in movement, but others will be found to be exceedingly lively and able to creep up the sides of the jar and make their escape in a surprisingly short time. Further modifications of the foot will be mentioned later.

THE MANTLE CAVITY

Now let us place the animal with the foot below and the head facing us. The spiral visceral hump will point back and away from the observer. The mantle covering the visceral portion is thin and translucent like an ordinary skin, but at the base of the visceral mass the mantle suddenly thickens very greatly, and spreads over the dorsal portion of the foot or the body like a cloak. The space between the body and the loose-lying mantle is called the mantle cavity, and within this area are to be found several important external organs. To find these it is well to cut the mantle flap in a straight line, beginning just back of the head and ending at the point where the mantle is attached to the body. This will most easily be done with scissors. Having thus divided the mantle in front, throw back the two flaps. On the right-hand side (left of the animal), and attached to the inner side of the mantle thus exposed, will be seen the branchiæ, or gills.

THE BRANCHIÆ, OR GILLS

They consist of a row of flattened filaments bound together at the base like the leaves of a book. The blood is conveyed to these gills by a large vein, and is then forced through the thinly walled filaments, being thus brought into close contact with the water, to which it releases its carbon dioxide, and from which it receives the life-giving oxygen. In certain gasteropods there are two sets of gills, one placed upon each side of the body [pg338] (as in the ideal mollusk); but the presence of two sets of gills only indicates, in these gasteropods, that the twisting process of the viscera, already alluded to as so remarkable a feature of this class, has not proceeded far enough to destroy the functional activity of one of the gills.

In general, it may be said that the breathing process of mollusks does not markedly differ from the respiratory methods of higher forms of animals. Whether the breathing is effected by gills or by a pulmonary sac, the essential features of the system are the same as in fishes or mammals. There are, however, some rather peculiar developments in the breathing system of gasteropods that are worthy of notice. The gills themselves differ throughout the various orders of this class both as to their structure and their relative position; in one of the orders (the Pulmonata) the gills have entirely disappeared, and are replaced by a pulmonary sac which fulfils the purpose of a lung.

It is a generally accepted theory that all land or air-breathing mollusks were originally marine, but by a gradual change in their habits have developed into terrestrial forms, losing their gills and acquiring in their place organs which correspond to lungs. The theory is supported by the fact that many species of marine mollusks live between tide-marks, and for several hours daily are obliged to maintain life outside of their native element. The Littorinidæ, which may always be found in abundance on both the east and the west American coasts, usually live high above low-tide line, and some tropical species of this genus actually live in the trees above the reach of high tide. They have gills just as in Buccinum or Fulgur, but the Littorina shell is strongly suggestive of certain land forms, and there is reason to believe that the genus is in course of evolution into a pulmonate. On the other hand, there are to be found in fresh water numerous genera which are true pulmonates, and which are obliged to come to the surface every few minutes to obtain air. One notable genus of marine gasteropods possesses both lungs and gills, and one marine form has entirely lost its gills and breathes only by means of lungs. It is quite likely that all mollusks are able to breathe more or less all along the exposed mantle surface, which is usually [pg339] crowded with capillaries with exceedingly thin walls. This very remarkable method of surface respiration is proved to exist in the nudibranch or shell-less marine Gasteropoda, for they possess neither gills nor lungs.

OSPHRADIUM

Lying just under the gills, and side by side with them, is a smaller, plume-like organ having the appearance of a smaller gill; it is called the osphradium. The office of this organ is not definitely known, but the supposition is that it is the seat of the olfactory nerves. The osphradia are not always present, but whenever found they are placed in close conjunction with the gills, in order, probably, that the animal may best determine the quality of the water brought by the siphon to the breathing-organs. In Buccinum the osphradium is especially prominent. In all mollusks the sense of smell is highly developed. A dead animal anchored to the bottom will very soon attract the carnivorous Mollusca from every direction. This is not a bad way to trap certain species that live upon rocky stations and are otherwise difficult to secure by the dredge.

On the left-hand side (right of the animal), and adhering to the under side of the mantle flap, which has been thrown back, a somewhat inflated and convoluted tube, the rectum, will be seen. It terminates in an opening just within the mantle-edge. By the side of this are the renal and genital openings.

Having now examined the external organs, we may investigate the internal anatomy of our subject. To do this thoroughly requires considerable skill, but for the purpose of merely discovering the relative positions of the principal internal organs a little care only is necessary. The work will be greatly facilitated by boiling the animal for a few minutes, for this serves to harden the tissues and to separate the various organs in a most satisfactory manner.

To begin, open the proboscis from the mouth, cutting back so as to expose the esophagus. It will be seen that the throat is long and very muscular. [pg340]

RADULA

Hidden among the red stripes of muscular fiber which line the inner surface of the throat will be found a fleshy strip covered upon one side with many transverse rows of chitinous teeth. This is the lingual ribbon, or radula. Remove as much of it as possible, and examine it with a hand-glass. The radula is a most important organ, and is a unique possession of Mollusca, except the pelecypods, or bivalves. Usually it lies coiled up like a spiral when not in use; its purpose is to tear and rasp food.

The radula has been the subject of much study by conchologists, and has furnished the basis for an arrangement of the numerous sections of gasteropods into somewhat well-defined groups. If the observer has a strong glass he will notice that each transverse row of teeth on the ribbon consists of a median or central tooth with several points or "cusps." Fulgur has a median tooth with three cusps; Buccinum one with six. On each side of the median tooth is a lateral tooth, which in Fulgur will be seen to have six cusps, and in Buccinum five. In many patterns of radulæ there is, besides the median and lateral teeth, still another paired row, called the marginals. In the accompanying figures are given some examples which show small sections of lingual ribbons. While all the radulæ of mollusks are capable of being grouped by their general characteristics, yet in no two species of mollusks are the radulæ quite identical. [pg341]

VITAL ORGANS, STOMACH, LIVER, RENAL GLANDS, ETC.

The digestive tract will be found to widen out a short distance back into a crop or stomach, and, continuing still further, to lose itself in a soft, brownish mass within the coiled spire, which is the liver. The very large size of the liver leads one to suspect that Fulgur and Buccinum must be voracious creatures to need so large an organ for the secretion of bile. In many species of mollusks the stomach and intestines are filled quite solidly, at times, with a gelatinous transparent substance called the crystalline stylet. Just why the digestive tract should be clogged with this substance no one has yet been able to explain, so here again is a chance for original investigation. The intestine curves about after reaching the liver, and comes forward again to appear once more as the rectum, clinging to the inner surface of the free portion of the mantle.

Closely associated with the liver, but differing slightly in color, is the gonad, or organ in which the genital products are formed. Situated dorsally and forward of the liver and gonad is a large renal gland, which may readily be detected by its peculiar structure. In some forms the kidney is closely associated with the gonad, and seems to coöperate with the latter in the generative functions.

HEART AND VASCULAR SYSTEM

To find the heart, make an incision into the body just at the posterior end of the gills. The heart is white and round, and is inclosed within a cavity known as the pericardium; it has a ventricle and one or two auricles, although in Buccinum and Fulgur there is but one auricle.

There is nothing remarkable about the vascular system to distinguish it from that of many higher forms of animals. It is, however, not completely closed—by which is meant that the blood is not always contained within arteries or veins, and that it does sometimes flow into other organs and floods certain other body-cavities, although the vascular system of mollusks is by no means so completely open as is that of insects and crustaceans. [pg342]

Having examined the animal which inhabits the shell and gained an idea of its anatomy, we may now turn to an inspection of the house which it has built for itself, and here we shall find a delightful subject for study.

THE GASTEROPOD SHELL

An industrious hour of collecting upon almost any beach will provide the student with an abundance of interesting shells. Putting aside the bivalves, the univalve or gasteropod shells remaining should be closely examined for the purpose of becoming acquainted with their various conchological features. The collector will see at once that he has a number of species that differ more or less widely in their general form, size, texture, and sculpture. Some shells will be long in proportion to their width, with many turns of the spire which probably terminates in a sharply pointed apex; others will be almost round, with comparatively few spiral turns which end in a blunt apex, giving to the specimen outlines suggestive of a dome. A wide range of characters will be found in the mouths or apertures of the shells, some being almost if not quite round, others oblong and with a notch cut into the lower portion of the opening, and others possibly with this notch extended into a sort of semi-inclosed channel. A first lesson in classification of the Mollusca may be taken by dividing the results of the first day's collecting of univalve shells into groups according to these prominent shell-characters.

A good knowledge of the parts of a gasteropod shell is essential to the student, and it can readily be acquired. Four specimens are given in the accompanying figures, representing highly divergent [pg343] types of marine gasteropods, and their respective characteristics may be noted by comparing them one with another: Fasciolaria tulipa (Plate LXXVI.), a Floridian shell; Polynices heros, a common species found on all the sandy shores of the American Atlantic coast; Murex tenuispina, an Indo-Pacific species much prized by collectors; and Acmæa testudinalis, commonly found in Maine and Massachusetts at low tide clinging to rocks.

The extreme top of the shell is called the apex, and it may be either sharply pointed or obtuse. Each turn is called a whorl; the last one, and always the largest, is called the body-whorl, the others collectively forming the spire of the shell. When the animal first emerges from the egg it is always provided with one or two whorls, which generally may be distinguished at the apex as smoother than the rest of the spire, and a faint line may be discovered where the shell began its growth after birth. These [pg344] first whorls of embryonic growth are usually referred to as the nepionic whorls. The interstices between the successive whorls are called sutures, and these lines of juncture may be shallow or deep according to the convexity of the whorls. The sculpturing of the whorls is often of great complexity, and exhibits nodules, varices, ribs, revolving striæ, spinous processes, and lines of growth. It frequently happens that there is a complete absence of any sculpturing whatever, the whole surface of the shell being perfectly smooth, save for the faint lines of growth to be detected only under a magnifying-glass. The outer edge of the mouth or aperture of the shell is called the outer lip. This may be more or less thickened, expanded, or simple. The inner lip is called the columella, and may be greatly extended anteriorly. When the mouth of the shell is round, and there is no notch or indentation either above or below, it is said to be continuous.

The anterior canal is for the accommodation of the siphon of the animal, which, as noted above, may be very long or almost entirely absent; therefore the character of the shell generally indicates whether or not the animal itself possesses a long siphon. There is in some forms a notch at the upper extremity of the mouth, which is for the accommodation of the anal discharges. When present it is called the posterior canal.

It will be noted that all the specimens figured as examples, save one, are spiral, the coils revolving about an imaginary axis. When the whorls are not too closely coiled there is left open to the view a hollow space throughout the entire length of the shell, which is called the umbilicus. When the coils of the shell are very compact there is no umbilicus to be seen. The umbilical opening may be very large, giving a clear view of the inner surfaces of all the whorls right through to the apex. The usual gasteropod shell is in reality a hollow tube wound about an imaginary axis. Since the tube increases in size as it progresses, the base of the shell is necessarily wider and larger than the apex. Thus all gasteropod shells may be reduced in shape to the single type of a cone or top, modified by the excessive length or shortness of the spire, or otherwise altered by special peculiarities. In Polynices duplicata (page 368), it will be observed that while the [pg345] umbilicus is fairly large, its external opening, in the adult shell, has been almost completely closed by a callous process thrown off from the inner or columellar lip.

Gasteropod shells may be sinistral or dextral, according as the whorls turn to the left or right. The great majority of marine species are dextral, having the opening on the right, although a few species exhibit the curious property of being constructed upon either the one or the other plan without apparent reason. Sinistral specimens of many normally dextral species have been discovered, but they are so rare as to warrant the belief that such specimens are merely deformities or monstrosities resulting from some accident of birth.

The collector will soon learn to distinguish between young and adult specimens, for those finishing touches of wonder and beauty which the mollusk gives to his protective covering are made only by the adult. The outer lip of young gasteropod shells is usually thin and fragile; even if slightly thickened, it has an unformed or unfinished appearance.

Shells differ greatly in their structure, many species being porcelanous like china, others glassy, and many more are of a softer chalky composition. In the latter case the shell is usually covered with a thick membranous skin, which, when removed, leaves a dull, lusterless, white body beneath. Shells of this texture, when cast upon the beach, soon yield to the weathering action of sun and air. The porcelanous shells are composed of successive layers of carbonate of lime, throughout which is a filmy membranous framework of a substance similar to that of which the covering of the Crustacea is formed. The mode of deposition of the various layers of crystalline calcic carbonate and the peculiar lineation of their outer surfaces give rise to the iridescent or nacreous appearance of some shells.

With the exception of those species in which the mantle of the animal is extended over the edge of the aperture and more or less envelops the entire test, there is an outer skin of membranous or organic matter which overlies the surface of the shell. This skin is sometimes quite thick, often hairy, and is usually of a dull greenish- or brownish-yellow color. In many genera this [pg346] outer covering of the shell is excessively thin. In old specimens the epidermis is usually worn away from the apical whorls. It often happens that the shells of the most exquisite colors and markings are thus rendered somber and unattractive by their tenants during life; when the animal dies, or when such specimens are kept in a cabinet for a period of time, the epidermis dries, cracks, and falls off, revealing the wealth of color and design beneath.

The growth of the gasteropod shell is accomplished by the exudation from the margin of the animal's mantle of a liquid containing the shelly matter in solution. The mantle-edge is provided with a complicated system of glands and pores, from which is secreted this "stony liquor." This more or less viscous liquid, containing the carbonate of lime and the other inorganic materials of which the shell is composed, hardens upon exposure, and the shelly matter is then deposited in crystalline form around the edges or lip of the shell aperture. The gasteropod shell therefore grows by the continual building out of its aperture through successive depositions of shelly matter at the extreme edge of the lip. At the extreme edge of the mantle margin are situated those glands which secrete the materials for the epidermis of the shell, and as one would therefore expect, this outermost layer of epidermis is first produced in the advancing growth of the shell. There also are situated the pigment-glands, which produce the color-secretions. The various layers of the shelly substance are successively deposited inside the mouth of the shell by glands situated just back of the extreme edge of the mantle margin. Thus in the growth stage, if one could examine closely the aperture of a gasteropod shell, one would observe at the extreme tip of the lip this projecting epidermis, just beneath it and just inside the aperture a thin deposit of shelly matter, just beneath this, and farther in, another layer, and still farther in a third layer.

The growth of nearly all gasteropod shells is marked by periods of rest. During the inactive seasons the creature may thicken the edge of the aperture to a greater or less extent by an extra deposit of shelly matter, for otherwise the thin lip might soon be [pg347] injured or broken. These places where the lip was thickened, as a temporary protection until the young animal decided to continue building, appear on the surface of adult shells, and persist as varices, "raised lines of growth," "longitudinal ribs," etc. Such forms of sculptural markings generally occur at equidistant points and preserve a scheme of regularity which would indicate that the periods of rest were of seasonal occurrence. All irregularities and all surface features of the external shell simply reflect certain peculiarities of the mantle margin of the animal; all spinous processes, for instance, as in the marvelous Murex tenuispina, indicate the existence of finger-like processes extending from the mantle margin, which once occupied the hollow thorns projecting from the shell. When the outer surface of a shell is devoid of any sculpturing and is perfectly smooth, one may assume that the mantle margin of the animal was simple. If the edge of the lip has a crenulated appearance and the surface of the whorls is decorated with revolving ribs, the mantle margin was probably folded or wavy. There can be no doubt but that the entire mantle surface is provided to some extent with glands for the secretion of shelly matter, for if any portion of the shell is accidentally injured the animal soon repairs the break with a calcareous deposit. But such repairs are never homogeneous in texture with the other parts of the shell of normal growth; the patches are never covered externally with an epidermis, and they are always devoid of color. The function of the epidermis is to protect the calcareous shell from the corroding agents contained in sea-water. Hence it is that, when the epidermis is removed, "dead shells" exposed to the influence of the water or the weather soon lose their brilliancy and luster, and become undesirable for specimens either for the cabinet or for study. It often happens that living shells, inhabiting a region where, for one cause or another, the water is highly charged with impurities of an acid nature, are discovered to be badly corroded about the apex, where the epidermis is thin and likely to be rubbed off. For this reason specimens collected in harbors near large cities or near the mouths of rivers are apt to be poor and defective.

The inner surface of all shells, if not actually nacreous, is [pg348] always perfectly smooth. When foreign substances, such as grains of sand, enter the shell and cannot be removed by the animal, the irritation caused thereby to the soft, fleshy creature induces discharges of a liquid from the glandular surface of the mantle, which hardens about the offending substance and glazes it over with a smooth, pearly deposit.

Acmæa testudinalis (page 343) presents a special type of gasteropod shell which is found in several families. Here the spire seems to be wholly absent, and the entire shell consists of but one large body-whorl. There are very many of these patelliform species, inhabiting many seas and belonging to many different genera, and in nearly all cases their embryonic shells display a spiral form. After birth the animal does not build his house upon the spiral plan, but expands the shell into one large shield-like covering. The student, however, must not presume that Acmæa is an ancestral type just because the simple character of the shell is suggestive of the model chosen to represent a schematic mollusk; anatomically Acmæa presents the complications of body-torsion which show a very considerable evolutionary change, and indicate that its simple shell is probably a degenerate form of a once more highly developed and convoluted one.

The forms, the architecture, and the painting of gasteropod shells are so infinite in variety that it would be unwise to attempt a description of their marvels. A close observer of nature's works soon becomes prepared for every surprise, but he never ceases to be charmed and fascinated by his new discoveries. The careful student alone can learn really to see and appreciate the wonders of nature, and this is especially true in the study of the Mollusca.

CLASSIFICATION OF GASTEROPODS

The Gasteropoda far exceed all the other divisions of the Mollusca in the number of their genera and species. Apparently this has not always been the case. There is evidence tending to show that in past geological epochs the pelecypods (the bivalve shells) outnumbered the gasteropods, but that in the course of time the increase in the genera of gasteropods has been more [pg349] rapid. To judge also from the very large number of extinct families among the cephalopods, which once flourished in astonishing abundance, it would appear that they are a dying race.

The classification of the Gasteropoda is primarily a division into three great orders: the Opisthobranchiata, the Prosobranchiata, and the Pulmonata. The Pulmonata, which include the land and fresh-water gasteropod shells, are characterized by the presence of a breathing-sac, or lung, instead of gills. They are, therefore, essentially air-breathers, and would perish if kept too long under water. The Opisthobranchiata and Prosobranchiata are marine, and, like all animals which breathe by means of gills, soon die when removed from the water. We have already noted, however, how some genera of marine gasteropods that find their station about high-tide mark are able to live for considerable periods out of the water, notwithstanding the fact that they are fully equipped with gills and not possessed of lungs. Indeed, there is one large family of prosobranchs (the Cyclostomatidæ) that has become entirely terrestrial in habit, its members having lost their gills and acquired lungs, but their organization otherwise is so essentially that of the prosobranchs that they have never been considered as pulmonates.

The main difference between these two orders of marine gasteropods is that in the prosobranchs the breathing-organs (the gills) are placed in a position forward of the heart, and the degree of torsion (page 330) characteristic of this molluscan class has been continued until the auricle of the heart is in front of the ventricle. There is always a shell, usually spiral, and, with few exceptions, an operculum. In the opisthobranchs, on the other hand, the relative position of the heart and gills is reversed, and they further differ from the prosobranchs in that the sexes are always united in each individual. The opisthobranchs are not always provided with a shell. One division of the order, known as the "nudibranchs," are entirely naked. These are commonly called the "sea-slugs," and are to be found crawling about the marine vegetation in shallow water, in tide-pools, and on the piling of old docks. Curiously enough, the sea-slugs (see page 354) have no gills at all, but, having lost these apparently essential organs, are [pg350] enabled to "breathe water" through their skin. They are wonderfully beautiful creatures, and the collector must not fail to secure some specimens, put them into a jar of sea-water, and watch them expand.

There are other more superficial differences between the prosobranchs and the opisthobranchs, which will enable even a beginner to distinguish them at a glance. When the latter are possessed of an external shell, it is bulbous, generally glassy, and with a simple lip, the aperture extending the entire length of the shell. Again, the mantle or the propodium of the foot is greatly extended and usually covers the shell almost wholly.

With the exception of the nudibranchs, which are common all along the Atlantic shore, especially north of Cape Cod, there are very few opisthobranchs to be found in American waters. Their shells are not very abundantly found anywhere, though in Florida there are two or three species which an untrained collector might discover.

Practically all the gasteropod or univalve shells that will be taken by the ordinarily expert collector along the shore are prosobranchs. This order includes the great majority of marine gasteropods, and is entitled to the distinction of claiming, in the great number of its genera and species, the most startling eccentricities of form and color to be found among the Mollusca, if not among all marine invertebrates.

Only those species which are actually abundant on the Atlantic and Pacific shores of the United States, and which are likely to be found by the untrained collector, are selected from the long list of forms which belong to the three faunal regions involved.

ORDER OPISTHOBRANCHIATA

Suborder TECTIBRANCHIATA

As has already been remarked, shell-bearing opisthobranchs are not abundantly represented in number of species in North American waters. South of Cape Cod, in muddy bays and well-sheltered places, the little shell, Haminea solitaria, may, however, often be found in considerable numbers.

Closely allied to these outer-shell-bearing opisthobranchs is a large and important group of tectibranchs, known as [pg352] "sea-hares." They have a mantle so greatly developed that it actually covers the shell, and its edges unite and fuse over the top. The shell, in consequence, having almost ceased to be of use as a protection, has degenerated into a mere horny plate, and has lost all resemblance to the ordinary gasteropod shell. Having practically lost its protective office and become a mere internal plate, it is quite probable that it will in time wholly disappear. The gills of the sea-hares are concealed under a flap of the mantle, their position being posterior to the heart. The most conspicuous representative of this type of tectibranchs in the United States is the following:

Suborder NUDIBRANCHIATA

The opisthobranchs are divided into two suborders, the second of which is called Nudibranchiata. The name is well chosen and very suggestive, for it means "naked or exposed gills"; but this anatomical feature is only one of the peculiarities of this suborder. The nudibranchs are commonly known as "sea-slugs"; for, like the land-slugs, which are also true mollusks, they possess no shell at all. That they at one time carried a shell is evident from the fact that they are born with a rudimentary testaceous covering, which soon afterward disappears.

A striking peculiarity of the nudibranchs is that the conventional molluscan mantle is not usually apparent. Instead of seeing the usual flaps or folds of the mantle which more or less encircle mollusks, and which one seems to have a right to expect, [pg353] they are entirely absent, and the body of the sea-slug assumes in consequence a worm-like appearance. Other notable features of the nudibranchs are the great number of tentacular processes that usually project from the dorsal region of the animal, and, in many of the genera, an entire absence of gills. When the gills are present, as is the case in several of the nudibranch families, they are not placed along the side of the animal, where one would naturally look for them, but are arranged in the form of a rosette of plume-like processes situated in the posterior dorsal region, or, in other words, on the animal's back.

Nudibranchs are commonly to be found all along the Atlantic and Pacific coasts of North America, and more especially in the colder waters north of Cape Cod. They are essentially littoral, and live upon algæ in shallow water, upon eel-grass in sheltered places, and in tide-pools, where there is more or less vegetation. They crawl about the fronds of algæ, or swim, foot upward, with a gentle and undulating motion, or, when caught between tides, may be seen clinging to the under surface of rocks. Protective resemblances have been so remarkably developed in the nudibranchs that they are not always easy to discover; indeed, one may actually be looking at one for some time without suspecting it to be other than some torn fragment of seaweed.

There are many species belonging to several genera which frequent the Maine and Massachusetts coasts, but those most likely to be encountered are the following:

When discovered at low tide upon moist seaweed or stones, or when disturbed in the water, nudibranchs often appear like small lumps of jelly-like tissue, without a single attractive feature. It is only when they are placed in a jar of sea-water and left unmolested for a few moments that they unfold their beauties to the view. On the Pacific coast there are numerous species of nudibranchs, occupying corresponding shore stations and exhibiting the same degree of high coloration. There are over a thousand species of sea-slugs scattered about the various seas. They find their greatest development in tropical waters, and for brilliancy of tint and variation in form are unequaled by any other class of animal life, save perhaps the butterflies.

ORDER PROSOBRANCHIATA

To this exceedingly large and comprehensive order of gasteropods belong the great majority of univalve mollusks. In point of number of genera and species and in abundance of individuals, the prosobranchs probably exceed all the other orders of mollusks combined. They may be called the typical gasteropods, the shell being univalvular and generally spiral, and the animal exhibiting the singular torsion of the visceral mass which has placed the breathing-organs forward of the heart. They are provided with an operculum (placed upon the posterior dorsal portion of the foot), which is used to close the aperture of the shell against [pg356] enemies when the animal retires within its fortress. They are all marine except a very few families, which, supposedly of marine derivation, have become terrestrial in habit.

The prosobranchs are further subdivided into suborders according to certain peculiarities of the heart and breathing-organs. There is a group of these prosobranchs which gives evidence of an inferior degree of that visceral torsion which is always found in the gasteropods. In this group, or suborder, the heart has two auricles, and there is a pair of gills instead of only a single one. Other internal organs are paired just as they were represented to be in the schematic mollusk. This group also seems to show its primitive character in the want of a proboscis and a siphon, or, in some families, by having the ventricle of the heart traversed by the intestinal canal, just as in the lower class of mollusks, which includes the clams and oysters. For the most part the shells of this group are not typically spiral, but are patelliform, shield-like coverings, with only a suggestion of a spiral form at the very tip of the apex. This group of primitive prosobranchs is included in the following suborder:

Suborder DIATOCARDIA

The first family to be noted is the Acmæidæ. Its principal genus, Acmæa, is well represented on both the east and the west coast of the United States.

This family is closely allied to the Fissurellidæ. The species are known on the Pacific coast by the name of abalone shells, and in England and the Channel Islands as ormers or sea-ears. There are no species of Haliotis on the east coast of the United States, but one has recently been dredged at a considerable depth in West Indian waters. This family, with the last, possesses the striking anatomical feature of having the heart traversed by the digestive tract. It also has two gills, the degree of torsion in the visceral mass not being sufficient to have crowded out and destroyed the original right gill. The shell is spiral, but is so greatly flattened, and the body-whorl is so greatly extended, that the shell quite loses the spiral appearance. Along the dorsal side of the shell is a row of holes, through which project numerous tentacular processes from the mantle. The outer surface of the shell, before it is polished, is usually rough and unattractive, but within, when the [pg359] animal is removed, it displays a most beautiful and highly colored nacreous surface. The spot near the center of the inner shell surface where the muscles of the foot were attached is usually most brilliantly colored. The shell of the abalone is susceptible of taking a very high degree of polish, and is extensively used in commerce for colored mother-of-pearl and for inlaid work. Haliotis is a vegetable-feeding genus. They cling with great tenacity to rocks about low tide, and it requires skill to remove them without breaking the shell. There are several species in California. The Chinese use the abalone for food, and have waged a persistent war upon the family along the Pacific coast until the specimens are not nearly as common as formerly. They are also eaten in France and in Japan.

This is one of the largest and most interesting families of the Mollusca. It contains many apparently widely separated genera and a host of species, which for the most part are littoral, the majority actually living between tide-marks. The typical trochid shell is top-shaped or pyramidal, having a broad base and many closely wound flat whorls terminating in a sharp apex. All the trochids are nacreous within the aperture—a character which is constant throughout the family. The animal has but one gill (the left), a short snout, and often frontal lobes on the head. The edge of the mantle or the epipodial line of the foot is usually ornamented with from three to five cirri. The tentacles are [pg360] long and slender, with short peduncles for the eyes; the operculum is corneous, with a central nucleus. The animals are herbivorous, feeding upon algæ. The trochids are essentially tropical shells, and the most of the genera which are comprised in the family are only to be encountered in the warm waters of the Pacific and Indian oceans. Some forms are very beautiful, and frequently are used as mantel ornaments, and the shells of one little species, which is opalescent in its coloring, are still extensively gathered in the East Indies, to be polished and strung like pearls in necklaces.

On the Atlantic coast north of Cape Cod the trochids are represented by the genus Margarita, with five or six species. The shells are small, thin, and globosely depressed, with smooth or transversely striated whorls. The aperture is nearly circular, with a simple lip.

This genus is better represented on the Pacific coast of the United States than upon the Atlantic. It comprises a series of marvelously beautiful shells, often exquisitely colored. They are regularly conical or pyramidal in shape, with flattened bases. One never tires in the search for calliostomas. They are not common enough to cause one to lose interest, and whenever a good specimen is captured it seems as though one had found some gem cut and polished by nature's skilful hand and prepared for a place of honor in the cabinet.

This genus is represented in California by several species, the commonest of which is probably C. funebrale—a doleful name, no doubt given on account of the jet-black color.

This family is very closely allied to the trochids, the most striking difference being in the operculum, which in the Turbinidæ is calcareous and usually smooth and very convex on the outside. [pg363] The shells are nacreous within, and the animal, with its rows of waving cirri upon each side, is very suggestive of Trochus. They are, for the most part, shallow-water or littoral forms.

The Neritidæ are strictly littoral forms, almost entirely confined to the warmer waters of tropical seas. The animal preserves the usual diatocardian features—has a short snout and long tentacles. Unlike the trochids and Turbo, it has no cirri along the epipodial margin. The shells are peculiarly shaped, the spire being greatly flattened and scarcely noticeable on account of the unduly large development of the body-whorl; thus the shell takes on a decidedly patelliform appearance. It is without an umbilicus. In the principal genus Nerita the outer lip is sharp on the edge, but greatly thickened just within.

The genus Neritina is very closely allied to the last, having quite the same form of shell; but it is usually more globular and [pg364] variously ornamented by bright spots or zigzag lines of coloration. The neritinas have acquired the habit of ascending rivers, until they have become almost wholly a brackish- or fresh-water genus. The metropolis of this genus is in the South Sea Islands, where it attains a wonderful development in the clear running streams of the volcanic islands.

The prosobranch gasteropods thus far considered (belonging to the suborder Diatocardia) all show by their anatomical structure that the process of visceral torsion, though carried very far within them, has not been complete enough to crowd out and finally destroy one of each of the paired organs. Both auricles of the heart (with some exceptions) were left intact.

Suborder MONOTOCARDIA

In this the second suborder of the prosobranch gasteropods, the twisting visceral process has been carried to the extreme. The heart has but one auricle. There is but one gill (on the left side), and this is attached to the inner side of the mantle flap. In other respects the presence of certain specialized organs would probably indicate that gasteropods belonging to this suborder are a step higher in the scale of life than those which belong to the Diatocardia.

The genus Janthina has an exceedingly thin and semi-transparent shell, deep violet in color on the base and lighter blue on the spire. An interesting feature of this genus is the mode of depositing the ova. The female exudes from a gland in the foot a [pg365] glutinous secretion which hardens in water, and, being filled with air-bubbles, constitutes a float. On the under side of this are deposited the eggs in rows of little capsules. While attached to this float it is impossible for a Janthina to sink, and hence it is that so many of these creatures are sacrificed in onshore gales of wind.

The shells of Scala have such a peculiar scheme of decoration that once seen they can never be mistaken. They are generally pure white, with well-rounded whorls, all of which are crossed at even distances by greatly elevated and smooth ribs. Each rib represents a rest-period, when the creature thickened the rim of the shell-aperture. The aperture is generally round, with a continuous lip. The animal has a retractile proboscis and long, slender tentacles with eyes at the outer bases, and is a predaceous, [pg366] carnivorous creature. Some Asiatic species of this genus, remarkable for their beauty and rarity, have been greatly prized by collectors. A single specimen of the now well-known S. pretiosa of China has been sold for two hundred dollars—a fancy price, indeed, for a shell which can now be bought for a dollar! There are over fifty species of Scala on the Atlantic coast, but most of them are either rare or belong to a zone of deeper water; there are, however, four or five species which are exceedingly common.

This large and interesting family is well represented in the Atlantic waters of the United States, but its more beautiful members live in the tropics. The New England and New Jersey species are dull in color, but offer much of interest to the collector and student. The foot is enormously large, and carries in front a great shield-like fleshy process, which curves back over the head of the animal and serves as a plow in pushing its way through the heavy wet sand of the beach. When the creature is thus seen extended in the act of crawling, one wonders how it is possible for it to withdraw so great an amount of body into its shell; but if it is suddenly seized or irritated, it will quickly [pg367] demonstrate its ability to hide itself completely within its house and to close the door very effectively by means of its operculum. The eyes seem to be wanting, or they are concealed under the skin of the head. The shell is usually quite large, with a depressed spire and well-rounded whorls—especially the body-whorl, which appears to be greatly swollen. The umbilicus is usually open and moderately large, the lip simple.

A very interesting species of this genus occurs on the east coast, sparingly in New Jersey, but very abundantly south of Hatteras. Sigaretus is a modified Natica. The spire is flattened and minute. The body-whorl, being greatly expanded, gives a wide, flaring, oblique aperture. The shell is ear-shaped and white, with fine revolving lines. There is no umbilicus. The operculum is small and rudimentary. The animal is large, with an enormous foot and greatly developed propodium, and is a sand-dweller. The common east-coast form is S. perspectivus. (Plate LXVIII.)

Crucibulum has a peculiar rounded shield-like form, with a very small apex on one side. Within there is a cup-shaped appendage attached by one side to the inner margin of the shell. This latter feature at once determines the genus.

Littorina is probably the most characteristic genus of Northern littoral regions. Together with some of its allied genera it is also, probably, equally characteristic of various tropical littoral faunas all over the world. The family comprises strictly between-the-tides genera and species. Indeed, it is suspected that some species of Littorina are making very fair progress toward a terrestrial condition, for they actually live above high-tide mark,—even in the branches of overhanging trees,—and must certainly pass days at a time out of their natural element. That such a transformation is possible need not for a moment be doubted, for there are many land mollusks to-day that give abundant evidence of having been at some past time aquatic or marine species. These changes in nature are constantly going on, and the gradual substitution of a lung for a gill is no very startling metamorphosis. [pg371]

The littorinas fairly swarm in favorable localities upon all shore stations. In Maine and Massachusetts the bold, rocky coast furnishes a home for several species. Often the rocks at low tide are black with them; the algæ that cling in wet masses to the exposed rocks are alive with them. One cannot walk about in such localities without crushing hundreds of specimens. Sometimes they will be found clinging in clusters upon the piling of old wharves, or crawling about the bottom at or about the low-tide mark. The best specimens of Littorina are found in stations where they are bathed twice a day by pure, uncontaminated sea-water; those living near the mouths of streams, or where the water is brackish or impure, are usually small and degenerate. They are vegetable feeders, and have received the common name of "periwinkles." In Great Britain they are used among the poorer classes for food. The animal has a short, broad muzzle, and eyes at the outer bases of the tentacles. The foot is longitudinally grooved, and there is a rudimentary siphonal fold in the mantle. The shells are turbinated, usually heavy, few-whorled, and with a round aperture.

Closely allied to Littorina is the genus Lacuna, one species of which, L. vincta, is very abundant on the New England coast. A curious and distinguishing feature of this genus is the umbilicus, which forms a lengthened groove along the columella. L. vincta rarely exceeds one half of an inch in length, and is thin, with a pointed spire of five whorls. It is either of a uniform horn-color, or purplish, or banded with chestnut. It may best be found upon marine plants in sheltered places, or may sometimes be gathered in quantity from the roots of Laminaria washed in by storms.

The specific representatives of this genus are mostly tropical. T. nodulosus is abundant in Florida. It is about one half of an inch long, and has the flattened columella and round mouth characteristic of Littorina. It is decorated somewhat elaborately by revolving rows of nodules which cover the entire shell. Its station and habits are the same as those of Littorina.

In this family we meet with a somewhat new type of shell—the long, turriculate shell, with many whorls and with a channeled [pg374] aperture. The Cerithiidæ include a large number of genera, mostly tropical in distribution. Their shells are usually highly ornamented in various schemes of sculpture, but they lack beauty in color. The animal is provided with a siphon, as is indicated by the anterior canal of the shell. The operculum is corneous, with a nearly central nucleus.

These are allied genera, having numerous species upon our coasts, but the shells are so small that the inexpert collector is not likely to notice them. Hosts of these minute, turreted, decussated, blackish shells are to be found on the wiry grasses of salt-marshes. They are also found on algæ at low-water mark. In Triforis the whorls turn to the left. Range from Cape Cod to South Carolina. [pg375]

This is a particularly interesting family, but it is tropical, and is represented on the shores of the United States by only one [pg376] genus, Strombus, of which we have but a few species. Strombus is a scavenger,—a buzzard among mollusks,—and its sense of smell is evidently very acute. Its eyes are much more highly developed than the usual gasteropod visual organs, and they are placed at the tip-ends of two very substantial eye-stalks or-pedicels. The tentacles are slender and project from the eye-pedicels. The foot is curiously developed; that portion of it which would naturally constitute the creeping-disk is exceedingly small, but the metapodium (the hinder part of the foot, upon which the operculum is situated) is very large. The corneous operculum upon its end, which is far too small to close the entrance of the shell when the creature retires within it, looks like a claw. Instead of creeping along the sand, Strombus proceeds by jumps or awkward leaps, turning its heavy shell first to one side, then to the other. The shell is usually heavy, with the outer lip greatly thickened.

Cypræa is one of the "aristocratic" genera. Whether the shell or the animal itself is considered, there is probably no genus of mollusks which offers so much of beauty and interest to the collector and student. The genus is a tropical one, and finds its metropolis among the coral-fringed islands of the equatorial Pacific. Despite their brilliant colors and general attractiveness, the cowries—for such is their popular name—are very modest and shy; they prefer to hide among rocks, where they may be secure from molestation, for probably their conspicuous appearance is a real source of danger to them. In the animal of Cypræa the mantle is provided with two large lateral lobes, which are reflexed and meet over the top of the shell; thus, when the mantle is fully extended, the shell is entirely concealed. These mantle lobes are often furnished with numerous forked, tufted, or ramified filaments. The foot is long; there is no operculum. The color of the animal is often very striking in its intensity. A description of the cowry-shell is hardly necessary, so familiar is every one with it. A deposit of enamel is made all over the shell, and its painting and decoration, usually very elaborate, is reserved for the adult as a final process in the artistic completion of its home. The aperture is as long as the shell, is channeled at both ends, and is toothed along both margins. The spire is insignificant and is concealed by layers of enamel. In the young the shell has a very different appearance, resembling a sharp-lipped Oliva, and its scheme of coloration may be entirely different from that employed by the adult.

Among the Cypræidæ are many remarkable species. The splendid Cypræa aurantia, a native of the Fiji Islands, is one of the shells most sought after by enthusiastic collectors. The natives [pg378] learned its value long ago, and hold specimens of it at very substantial prices. It is worn as an ornament by chiefs and as a mark of distinction. The well-known C. moneta, also a native of the Pacific Islands, has been very extensively used as money throughout the South Seas and in Africa. There are many collectors of shells who confine their efforts almost exclusively to this and to one or two of the other "aristocratic" genera. From an esthetic point of view this is very natural, but biologically the less pretentious mollusks are quite as interesting.

Of the one hundred and fifty or more species in existence only three are to be found upon the Atlantic coast of the United States, and the chances are decidedly against the finding of any of them north of extreme southern Florida.

In the genus Trivia the shell is shaped in every way like that of Cypræa, but its surface is never smooth. In the middle of the back is a longitudinal groove, from which run transverse ribs, which continue around to and enter into the aperture. The shells are always small, never exceeding one half of an inch in length, and their color is generally reddish or brownish, passing to pink.

This small family furnishes two conspicuously handsome species belonging to the genus Dolium, which range from Hatteras southward into the West Indies.

The cassides, commonly known as the "helmet-shells," are carnivorous mollusks, which lead an active life in sandy stations, prowling about in search of bivalves, upon which they prey. They have a large siphon and a fairly large and extensible proboscis. The foot is broad and strong, being well adapted for plowing through the sand. The shell of Cassis is large, generally heavy and inflated, with a short spire and a short, recurved anterior canal. The lip is much thickened. Upon the Atlantic coast of North America there are four species of Cassis. They are all properly West Indian in their faunal relations, but have found lodgment on the American shore at various points. All of them have been taken in the neighborhood of Cape Hatteras, two of them in West Florida, and two in Texas.

It seems like making a long leap to pass suddenly from the Cassididæ to the Muricidæ. In the natural biological order, as it appears in our present state of knowledge, a host of families and genera intervene between these two. But they are omitted here, either because they do not conspicuously occur upon our own shores, or because they are free-swimming pelagic mollusks, which live only far out at sea and rarely are found on the beaches. The family Muricidæ is an exceedingly large one, including a [pg382] bewildering number of well-characterized genera. It has many representatives in every sea, but, as is apt to be the case, the finest and most striking species are tropical. The animal is not peculiar in any way, being altogether a conventional prosobranch gasteropod, with moderately long foot, and the usual tentacles placed upon a small head. There is a retractile proboscis, which suggests carnivorous habits. In reality the Muricidæ are perfect pirates among the Mollusca, attacking nearly every species they encounter, piercing its shell and devouring the unfortunate inhabitant. They live in rocky and gravelly places or about coral reefs. Their shells are seldom colored, except about the aperture. What the shells lack in color, however, they fully gain in oddness of form and in sculpturing. The anterior canal varies from a mere notch to an astonishingly long channel. The tendency to nodes, varices, spires, and varicose processes in general is a prominent feature of the family.

There are several genera, with numerous species, upon the east and west coasts of the United States, but we can do no more here than mention those which are very common.

Of this tropical genus there are two Floridian species—M. rufus and M. pomum. The genus has been very extensively divided into subgenera, based upon shell-characters alone. Some of these subgenera are usually accepted at full generic value, and their substitution for the old, well-established name Murex is to be expected. These two Floridian species fall within different subgeneric lines, and the student who goes to a museum to compare his catch with the labeled specimens on exhibition will probably be puzzled to find his two murices named Chicoreus rufus and Phyllonotus pomum respectively. But for our purposes the name Murex will do well enough.

The genus Urosalpinx is closely allied to Murex and Trophon. Several of its species are found on the east coast of the United States.

On the west coast of the United States occurs a striking development of a group of the Muricidæ of a curious foliaceous appearance, belonging to the genera Pteronotus, Ocinebra, and Cerostoma.

This is considered a subfamily of the Muricidæ, and the group therefore bears the subfamily termination -inæ. There is no vital difference between it and the subfamily Muricinæ. The operculum in the Purpurinæ has a lateral nucleus instead of a subterminal one, but beyond this there are no essential differences. The shell of the purpuras is generally heavy and solid, being adapted to a life among rocks which are exposed to the beating of the surf. There is a lack of that extravagant sculptural design so characteristic of the true murices, most of the purpuras being comparatively smooth, in order, no doubt, that they may offer as little resistance as possible to the rushing, seething waters of exposed rocky shores.

The Purpurinæ, like some of the murices, when mutilated, exude a reddish-purple fluid. On account of this, the ancient Romans used to gather great quantities of certain Mediterranean forms belonging to these families, place them in large mortars, [pg386] and grind them up, shell and all. A garment dipped in the mixture and then exposed to the sun would receive a rich purple dye. This was the basis of the famous "Tyrian purple." The process was lost, and was rediscovered many centuries later, but it was long ago abandoned in favor of the far superior modern chemical dyes.

This genus, which is very closely allied to Purpura, is almost wholly confined to the west coast of the United States. The name is given on account of a peculiarity, which has, however, already been noticed in Cerostoma, namely, a horn-like projection from the basal portion of the outer lip. In all other respects this genus is nothing but a true Purpura. [pg388]

This is a large family of small but often exceedingly beautiful shells. Their distribution is mostly tropical, but the list of North American species is a very generous one indeed if the deeper-water forms are included. The animal is quite the same as in the Buccinidæ, to be described later. (See also description of Buccinum undatum on page 330.) The shells are usually quite solid, with a long, narrow slit for an aperture; the outer lip is thickened on the inside, especially about the middle portion, and is deeply toothed; and the lower portion of the columellar lip is also ribbed or toothed.

These are familiar, and often very characteristic, littoral shells in all parts of the world. Where they exist at all they are generally to be found in astonishingly large numbers, sometimes even crowding out all other mollusks. They are exceedingly active and predaceous, feeding upon other mollusks, whose shells they bore through by means of the sharp teeth upon their lingual ribbon. The Nassidæ of the east coast find a relentless enemy in the small hermit-crabs, which attack them, drag them from their coverings, and then proceed to occupy the empty shells themselves; the torn and lacerated Nassa animal is thereupon leisurely eaten, a retribution probably well deserved. The animal of Nassa (the principal genus of Nassidæ) is peculiar in having frequently a bifurcated tail; or, to speak more correctly, the posterior end of the foot is terminated by two appendices. It has a long siphon, and eyes placed upon the outer sides and near the base of the tentacles. The operculum has serrated edges.

From the number of subfamilies and genera included in this exceedingly large and comprehensive family, it would almost [pg392] seem that it has served as a sort of dumping-ground for various groups of mollusks of uncertain biological affinities. Although the family has recently been reduced by the removal of several large families, it still remains a bulky one.

The animal is described at some length on page 330. It has no striking peculiarities. The siphon in Buccinum is fairly long; the eyes are placed about midway between the base and the end of the tentacles. It is in general a conventional prosobranch animal. The great majority of the members of this family have a boreal range and are found widely distributed within the colder waters of the world.

Of the two genera of this family which occur in American waters, Fulgur may be taken as the most characteristic mollusk of the American Atlantic fauna; that is to say, Fulgur occurs only on the American east coast. Its range is from Cape Cod to the West Indies. The two Northern species are F. carica and [pg395] F. canaliculata, both of which are exceedingly common in sandy shore stations from Cape Cod southward.

This family comprises a number of genera of mollusks which have a fusiform shell, with a long-drawn-out spire and a long anterior canal. The animal is in no manner remarkable; no essential differences are to be noted from the usual conventional type of gasteropod mollusk, represented in the two families last described.

This genus is of tropical range, and contains many species of shells which are more or less conspicuous for their large size or their beauty of form. Three species occur in Floridian waters, and all of them may be taken about low-tide mark on the sandy flats which are so characteristic of Florida bays and harbors. All of them are sluggish animals which crawl very slowly along the bottom or bury themselves almost wholly in the sand, leaving only the tip of the spire projecting slightly above.

The Volutidæ, like the cowries, are "aristocratic" shells. As was stated above, there are many collectors who have become so fascinated by the shells of a few of these "first families of the Mollusca" that they make great efforts and spend no small sums in seeking to complete their cabinet series of the rare and more beautiful forms. The Volutidæ certainly have very beautiful shells, and they are for the most part exceedingly rare. The reason of their rarity has no doubt something to do with their habits. They are probably largely dwellers upon rocky ground, where the dredge cannot reach them. There is but one species of Voluta upon the American coasts which is available to the shore-collector, and this is the well-known and much-sought-after V. junonia. The animal of Voluta has a very broad foot, and a head curiously divided into two lobes, upon which are placed sessile eyes. A remarkable feature of the genus is the lack of an operculum. [pg399]

This is a family of exquisite little shells. In point of beauty they would rival the volutes were they not so much handicapped by their small size. The largest Marginella is not more than an inch and a half in length, while the great majority of its two hundred tropical species do not exceed one half an inch. The animal is very similar to that of Voluta; indeed, the marginellas were until recently included in the Volutidæ. The shell is also suggestive of Voluta. It is porcelanous, highly polished, and shining like all shells which are covered by a portion of the mantle when the animal is extended. Forty-seven species of Marginella are recorded from the Atlantic coast of the United States. The marginellas frequent sandy or muddy sheltered spots, and may be collected between tide-marks. In California there are several species, which are so minute that it seems hardly worth while to attempt a description of them. They are white and very inconspicuous little shells. One is tempted, however, to speak of some of the fine marginellas of the Bahamas. The animals are quite as beautifully marked as the shells themselves, while the shell of one species is used in jewelry on account of its pearly luster suffused with the most delicate pink.

The genus Oliva is one of the favorites among collectors. It comprises smooth, highly polished, porcelanous, and oval shells with a deeply notched, long, narrow aperture. The columellar lip is usually heavily calloused and ornamented with oblique folds. The animal's foot is very large, and extends laterally into lobes which curve back over the shell. In front the propodium is very large, forming, as in Natica and Polynices, a sort of plow. The mantle lobes almost cover the shell when extended.

The genus Olivella resembles Oliva very closely in conchological characters, but the shells are, with few exceptions, exceedingly small, and usually have a somewhat more elongated spire than is the case in the genus Oliva proper. The animal of Olivella seems to be a degenerate, for it possesses neither tentacles nor eyes. In habit and station it resembles Oliva.

This is a comprehensive family of several highly diversified genera. Its most prominent genus is Conus, a name which indicates the principal feature of the shell, for it is almost an exact cone in shape. Conus, along with Voluta and Cypræa, is entitled to the honor of being considered an aristocrat among mollusks. There are about three hundred and fifty species known, mostly tropical and Indo-Pacific in distribution. The shells have many points of beauty and are often of very high coloration and eccentric markings. Some of the rarer forms are famous in conchological annals for the enormous prices which they have commanded. The rare and beautiful Conus gloria-maris once brought £43 ($215) at an auction sale in London. In all shells of Conus there is a notch at the upper edge of the aperture for the accommodation of a posterior canal. In some other genera of this family this notch becomes a more prominent feature. The animal has a well-developed foot, a retractile proboscis, eyes situated upon the tentacles, and a fairly long siphon. Upon the under surface of the foot is a conspicuous pore, which opens into a water-vascular system of the foot. Conus is accused of having a poison-gland connected with the radula and of having shown vicious traits when captured. The animals are shy, and remain most of the time in hiding, while their pretty shells during life are generally rendered obscure by a dull, colorless epidermis. There are but few species of Conus upon the Atlantic shores of the United States, and these are confined to the warmer waters of Florida and the Gulf of Mexico. [pg402]

The last family of the Gasteropoda to be considered is the Cancellariidæ, which has but one genus, Cancellaria. There are several species upon the east coast belonging to deeper-water zones, but one well-known species, C. reticulata, is very common on shore stations from Hatteras south. The shell is oblong and solid, with a moderate spire, and whorls slightly flattened below the sutures, and is very roughly granulated or reticulated. The aperture is narrowly ovate, and is ribbed inside. The columella has two very strong and prominent plaits. The color is white, banded and variegated with reddish-brown. Length an inch or more. (Plate LXXVII.)

CLASS SCAPHOPODA

Family DENTALIDÆ

In nearly all collections of shells from the northeast coast of the United States are certain specimens about one to one and a half inches long, pure white, and shaped very much like an elephant's tusk. They are round, hollow tubes, slightly curved, of larger diameter at one end than at the other, and with an opening at either end. There are two very common species of these tooth shells upon the New England coast, [pg403] Dentalium dentale and Entalis striolata. The first has a simple round hole at the smaller end of the shell, and is faintly marked by longitudinal striæ; the other is a smooth shell which has a notch-like fissure on the margin of the apical perforation. Neither of these species is, strictly speaking, a littoral form, for all the Dentalidæ range into deep water, many of them living only in the profounder depths of the ocean. But these two species are exceedingly common in the New England coastal waters, at very moderate depths, and may sometimes be found upon the beach cast up by storms. They live buried in the mud, and feed upon infusorians and all manner of microscopic organisms.

Upon the west coast Dentalium pretiosum is very abundant north of California. It is almost like the east-coast Dentalium, but is more slender. The Indians used to gather these shells and string them together upon long threads to be carried about and used as money. In California occurs Dentalium hexagonum, a very delicate little species with a slightly angulated shell.

The animal of the Dentalidæ is remarkable, and easily merits the rank of a separate molluscan class. It has no head, no tentacles, no eyes, no heart, and no gills. It is a mollusk because it has a mantle, a foot, and a radula. Its position, therefore, is between the Gasteropoda, which it resembles in its univalve shell and radula, and the Pelecypoda, to which it is related by the pointed foot and the absence of head and tentacles, and also by the symmetry which pervades its organization.

Upon either side of the mouth, just beneath the flap of the mantle, are bunches of ciliated, contractile filaments (captacula), flattened at the end, which are supposed to be breathing-organs, and are perhaps exserted for the purpose of catching food. [pg404]

The entire absence of such important organs as the heart and gills, together with the fact that they are undoubted mollusks, would indicate that the Scaphopoda are very degenerate animals. The circulatory and respiratory system of mollusks is typically of a high order.

A great many specimens of the Dentalidæ dredged in New England waters are dead shells, occupied by a worm which seals up the larger opening, leaving only a small aperture through which it protrudes its long white body. These must not mislead the collector into a vain search for a mantle and other molluscan characteristics of anatomy.

Some of the larger species of Dentalium from deep-sea stations are four to five inches in length. [pg405]

CLASS PELECYPODA

This is a large and important class of the Mollusca, comprising an extensive group of animals, which vary widely in structure. Next to the Gasteropoda, it is the largest class of the phylum in number of genera and species. The name indicates a "hatchet-shaped" foot, but in many cases it is a misnomer. Acephala, meaning "without a head," is also employed for this class, and is, perhaps, a better term. Lamellibranchiata, referring to the type of gills prevalent throughout the division, is another name often used. The popular name "bivalves" is an altogether correct one, for all the animals of this class have two shells. To the Pelecypoda belong the oysters, clams, scallops, mussels, and, in short, all the bivalve mollusks (the word "valve" meaning "shell"). The organization of a pelecypod is entirely similar to that of a gasteropod or a chiton in its fundamental or essential plan, but it differs widely from both in matters of detail. If the student will keep in mind the general principles of gasteropod or the amphineuran structure when he dissects his first pelecypod, he will quickly see that the latter is about the same as a chiton would be were it folded over from a longitudinal median line as axis along its back, so that the opposite mantle-edges would meet, and its various shell-plates would unite upon either side into a single valve; or it is very like a gasteropod made symmetrical, and covered upon its two sides by separate shells instead of covered over its top by one shell. The loss of head, eyes, and tentacles, the substitution of labial palps, the extension and greater development of the gills, the modification of the foot and mantle, and the presence of certain special glands in the Pelecypoda become mere matters of anatomical detail. [pg410]

Any large clam will serve for dissection. In the neighborhood of New York the edible species known as the "Little Neck" clam (Venus mercenaria), or the larger Mactra of the sandy shores, will answer the purpose very well. In Florida, Callista, Venus, and Cardium are all available. On the west coast the large, heavy Tivela crassatelloides is probably the best subject. The oyster (Ostrea) is a degenerate type; and the scallops (Pecten) and the mussels (Mytilus and Modiola) have certain special modifications of their organs which might prove confusing, so these genera are not recommended for dissection and study at first.

Boiling is apt to shrivel and distort the soft, fleshy animal of the bivalves, and it is far better to examine a fresh specimen. The surest way of opening a clam without injuring the animal is to break one of the shells by sharp taps of a hammer, using great care not to lacerate the body within by a too vigorous assault. Pick off the broken pieces after having separated them carefully with a knife from the mantle margin, to which they cling, and after having cut through the tough adductor muscles as close to the shell as possible. The subject for anatomical study is then prepared "upon the half-shell."

THE MANTLE

The mantle is generally very thin, often a fleshy film of the finest tissue, and adheres to the inner side of each valve. The outer rim of the mantle is thickened and free, i.e., is not attached to the shell. This free portion is capable of slight extension beyond the margin of the shell when the valves are opened and the animal is off guard. In many genera the mantle edge is highly ornate, being waved, crenulated, or fluted, or is beset with several rows of papillæ, and is often richly colored. Mr. Hickson, a naturalist, who traveled in Celebes, says that the brilliant coloring of the mantle margins of mollusks contributed largely to the extraordinary color-effects upon the coral reefs.

It will be seen that the mantle entirely incloses the animal at the back and sides, just as the cover of a book incloses the pages or printed portion. At the posterior end of the animal there is usually a point—or perhaps two points—at which the flaps of [pg411] the mantle lobes unite in order to form two openings. These openings are called the siphons.

SIPHONS

In some cases the mantle lobes do not actually unite to form regular siphonal openings, but in life the free mantle-edges have a way of adjusting themselves posteriorly to form functional siphons without actually coalescing. Usually, however, the mantle flaps not only unite posteriorly to form true siphons, but are capable at that point of varying degrees of protrusion from the shell, and when extended the siphons appear as two tubes. In some genera these siphonal tubes are very long; in others they are fastened together and surrounded by a tough, leathery integument, [pg412] which, like the siphons proper, is only an extended portion of the mantle-edge. The orifices of the siphons are generally papillaceous. These two siphons (for there are always two if there are any at all) are the anal or excurrent (upper) and the branchial or incurrent siphon. The function of the latter is to draw in the pure water to bathe the gills and to furnish food, while the office of the former is to eject waste materials and the water which has already passed over the gills.

MANTLE FUSION

Besides the points of juncture where the mantle-edges unite to form the siphons, the coalescence of the two mantle lobes may be extended, and they may become further united and fused together at other points. Indeed, the fusion of the mantle-edges may become almost complete; but it always leaves the siphonal openings and a third opening through which the foot may be extended. This opening for the foot is called the pedal opening, or orifice. In such cases, therefore, the mantle becomes much like a bag or sac. The degree of fusion of the mantle-edges appears to correspond closely with certain changes in the organization of the animal, and this feature must be regarded as a very important character. [pg413]

The figures on pages 411, 412, and 413 show the degrees of mantle fusion in various groups from the open to the almost wholly closed types. One (A, page 413) gives an example of very large siphons united together and protected by the tough, leathery integument. To the right of this cut may be seen the foot projecting from the pedal opening in the mantle. Another gives the two siphons of Cardium, the lower or branchial one being the longer. The mantle-edges below are fluted, and a large foot projects forward. Another shows two siphons of Scrobicularia, of the free and greatly extended type. Fig. B (page 413) illustrates the ventral portion of a pelecypod, which shows very well the most advanced type of mantle fusion. Besides the siphonal openings at the end of the long projection to the left, the only other opening is the very small orifice marked "2," for the accommodation of a small, insignificant foot. In the other figures different degrees of mantle fusion are indicated.

Before removing the mantle from one side of the specimen to be examined, note the two strong muscles which are at either end of the body. These are the anterior and posterior adductor muscles, their office being to hold the valves tightly shut. They are of great strength, as any one may prove to his satisfaction by attempting to open a clam. Through a long series of forms these two muscles approach each other in position, and in the scallops and the oysters there is but one adductor muscle, occupying a central position. Morphologically it is the survival of the posterior adductor.

THE BRANCHIÆ OR GILLS

Removing carefully the thin, fleshy mantle, the gills are exposed to view—that is, of course, the gills of that side of the [pg414] animal, for there are two sets, one upon each side of the body, or visceral mass, and lying between the body proper and the mantle folds. Each set consists of two plate-like bodies with a texture of reticulated or basketwork appearance. Thus there are the inner and outer right gills and the inner and outer left gills. If one gill is removed and carefully examined it will itself probably be found to be double, consisting of many filaments placed side by side and then doubled back like a row of hairpins, the filaments being united by interciliary processes, or by vascular channels together with more or less dense connective tissue.

The modifications of the pelecypod gills are difficult to follow, but the principle upon which they perform their duties is the same in all cases. The gill-filaments are all connected with a long vein, and, being hollow, admit the blood, which is aërated by close contact with the water and is then returned to another vein in immediate connection with the auricles of the heart. There is another function accomplished by the gills, which in some families seems to be quite as important as their respiratory one, namely, the office of giving lodgment to the ova while in process of development before hatching. At certain seasons the gills of a number of pelecypod genera become literally filled with eggs; sometimes this curious phenomenon extends to the mantle itself, and more or less to the entire surface of the animal. The eggs are first regularly ejected from the genital ducts and find lodgment upon the body-surface, but usually only upon the gills, where they remain as in a brood-pouch between the lamellæ of the inner and outer gills. When the eggs hatch, the free-swimming young escape from the mantle cavity. Probably not more than one individual in a million ever reaches maturity.

The figure on page 408 shows the mantle removed, exhibiting the gills, the foot, the labial palps, and the pericardium, inside of which is the heart. Removing the gills, we find exposed the body, or visceral mass, which, as in the Gasteropoda, is thickened below into the foot. A longitudinal section is shown on page 408, the visceral mass being sliced almost through the middle; a portion of the gills of the farther side shows below. [pg415]

THE FOOT

The foot undergoes great variation, from a strong, powerful organ capable of forcing its way through heavy gravelly bottom or burrowing deeply into the sand or mud, to the merest trace of a pedal organ. In the oyster the foot has become almost entirely atrophied; the stationary life led by the animal renders such an organ quite unnecessary. Excepting in a few families, the pelecypod foot is well developed. In a number of genera the foot contains a gland for the secretion of long silk-like or horn-like fibers, which are collectively called a byssus. The use of a byssus is for attachment to any object to effect a temporary or permanent lodgment. The accompanying cut shows Mytilus edulis, a common east-coast pelecypod, attached by its byssus to a piece of wood. Most bivalves having a strong byssus exhibit a feeble development of the foot; nearly all bivalves, however, show traces, sometimes only in the embryo, of a byssal gland.

The visceral mass contains the liver, the exceedingly large generative glands, the kidneys, etc., and through all this soft whitish or reddish mass the alimentary canal wanders about in a tortuous fashion, finally passing through the pericardium and the ventricle of the heart, and terminating just over and back of the posterior adductor muscle. [pg416]

The pelecypods have no head or tentacles, but the place of the latter is taken by two pairs of triangular flaps upon either side of the mouth. These are called the labial palps, and they no doubt operate by means of their ciliated surface to keep in motion the current of water over the gills and to the mouth.

As a rule, pelecypods have no eyes, but when eyes are present they are situated upon the edge of the mantle. The eyes are not highly developed organs, but they nevertheless appear to be very sensitive to light, for the bivalves which are so endowed will, when kept in aquaria, instantly close their shells when the shadow of a fish passes over them.

The heart lies in the pericardium and is situated dorsally, just in front of the posterior adductor muscle. It has a median ventricle and two lateral auricles, each connected with the branchiæ upon its respective side. It seems a curious economy that passes the intestine through the ventricle, but this is the case in the great majority of pelecypod genera. The vascular system is closed and is of a high order. It is probable that "breathing" takes place upon the inner mantle surfaces as well as in the gills themselves; for these surfaces are crowded with excessively fine and delicate capillaries, which bring the blood very near to the water. This power of "breathing by the skin" is quite characteristic of the Mollusca in general.

Having once familiarized one's self with the more prominent features of pelecypod organization, it becomes very interesting to examine anatomically every new form that is captured. Surprises are always in store, and sometimes the peculiar juxtaposition and relative sizes of the organs are a trifle confusing; but, upon the whole, the bivalve organization is simple and lends itself far more readily than does that of the gasteropods to satisfactory examination. Some of the more striking anatomical peculiarities are reserved for mention in the notes upon the various genera and species common upon our shores.

THE PELECYPOD SHELL

As has been seen, the testaceous covering of the Pelecypoda consists of two valves or shells which fit more or less closely and [pg417] firmly together and are placed one upon either side of the animal. The two valves are always held together tightly along a dorsal margin by a "hinge ligament," an exceedingly tough, leathery substance, and they are usually secured the more firmly by a system of interlocking teeth, which project from the hinge. The opening and shutting of the valves is controlled by the adductor muscles of the animal, by the ligament which binds the valves together, and by the cartilage, an elastic pad of rubber-like appearance which is lodged just within the hinge, and is compressed when the valves are closed together. Thus, when the valves are closed, there is always a strain upon the adductor to overcome the elastic resistance of the cartilage. When a pelecypod dies and the pull of the adductor muscles is released, the valves gape open.

The summit or apex of the valve is called the umbo, or beak. It is usually twisted to some extent, and in certain forms develops a suggestive spiral figure. The beaks of the valves are the points where the shell-growth begins, the secretion of calcareous matter being made by the mantle margin and deposited about the edges of the valves; the growth is therefore constantly away from the umbones.

The umbones usually point forward. In many species they touch each other over the hinge-margin or approximate very closely; in other species the hinge-margin is very wide and the beaks are comparatively far apart. The hinge-margin, lying adjacent to the umbones, is known as the dorsal margin of the shell, in contradistinction to the ventral margin, opposite the umbones. The anterior margin is the front edge and the posterior margin the hinder edge of the shells, through which the siphons may project.

When the umbones are about central in respect to the posterior [pg418] and anterior margins, the shells are said to be equilateral. When the two valves are almost exactly alike in size and shape they are called equivalve.

In many forms there is a heart-shaped space upon the dorsal margin of the closed valves forward of the umbones, called the lunule. Similarly placed back of the umbones is sometimes a more or less clearly defined space called the escutcheon. The outer surface of bivalve shells admits of infinite variety of sculpturing and ornamentation, ranging from a perfectly smooth to a heavily ribbed, nodose, spinous, or deeply decussated surface. The color-markings are often brilliant and eccentric.

The right and left valves may be distinguished by remembering that the siphons are always posterior, and that the umbones usually point forward.

The hinge of bivalve shells undergoes many variations in the different genera. The simplest type is a smooth edentate surface where the two valves meet and are held together only by the strong ligament. Generally, however, there is a system of interlocking teeth, those in the center of the hinge being the cardinals and those upon either side the laterals. In some forms there are rows of fine comb-like teeth along the hinge-margin, with no distinction between cardinals and laterals.

The object of these hinge-teeth is at once obvious, for they give a rigidity and increased strength to the entire mechanism, especially when closed. There is occasionally a saucer-shaped plate or platform just under the cardinal teeth and within the shell, called the fossette. Upon this rests the internal elastic cartilage.

Upon the smooth interior surfaces of the valves are always certain markings, which correspond to anatomical features of the animal and are consequently of considerable importance in the determination of the systematic position of the specimen. First, the well-marked impressions left by the adductor muscles will be noted; then a more or less distinct line which, describing roughly a circle, connects the two muscle scars. This line represents the points at which the mantle became detached from the shell. In other words, all the space within this pallial line (barring the [pg419] muscle scars) was, in life, covered by the mantle, which adhered tightly to it. The space between this pallial line and the outer edge of the valve was occupied in life by the free portion of the mantle. Frequently a depression in the pallial line toward the center of the valve is seen in the posterior end. This is called the pallial sinus, and marks the space occupied by the siphons. The pallial sinus is absent, moderate, or deep, according as the animal possessed no siphons, or small or large ones.

The length of bivalve shells is measured from their anterior to their posterior ends, while the height indicates the greatest diameter between the umbones and the ventral margin.

The greatest possible degree of variation exists in the structure of the pelecypod shell. Every degree of thickness from the most fragile, tissue-like structure to the very heavy and ponderous tests of some of the Veneridæ is to be found. There is also a range in size from the very minute Spheria to the giant Tridacna of Eastern seas, which weighs several hundred pounds. As in the Gasteropoda, there is fortunately a very close parallelism between shell and anatomical variations. One very quickly learns to place a bivalve in its systematic position by a mere glance at the shell alone. While the higher classification into orders, suborders, etc., is based upon anatomical features, the genera often and the species always are founded upon conchological or shell characters.

The Pelecypoda offer one of the most interesting fields for investigation and study among the invertebrates. Although by no means neglected, they have not received as much attention on the part of biologists as has been given to other phyla, or indeed to the other classes of this same phylum.

CLASSIFICATION OF THE PELECYPODA

Nearly every systematic writer upon the mollusks has attempted to give a good classification of the bivalves, yet none of the results is wholly satisfactory. The scheme now generally adopted is one based upon modifications of the gills, or branchiæ, and has practically replaced all the older classifications, which depended [pg420] upon the presence or absence of siphons, the degree of mantle fusion, the arrangement of teeth upon the hinge, the number of adductor muscles, etc. The idea of arrangement according to gill-structure is substantially this: the development of the gill from the simplest and most rudimentary type through successive stages to a higher, more complex, and presumably more efficient type, marks the natural progress or development of the pelecypod animal itself. By adopting the gill as a guide one follows, therefore, a natural method. Upon the other hand, the presence or absence of siphons, the shape of the foot, the number of adductor muscles, all depend merely upon the acquired habits of the animal, these particular features being subject to modification according to environment and changed conditions.

The five orders of the Pelecypoda are: Protobranchiata, Filibranchiata, Pseudolamellibranchiata, Eulamellibranchiata, Septibranchiata.

The first includes the simpler type of gill as represented in the accompanying figure (A). Its filaments are short and not reflected. The second, represented in Fig. B, has the filaments long, reflected, and connected (each filament to its adjacent ones) by means of surface cilia. The third type of gill resembles the last except that the ends of the filaments of the outer gill are attached to the mantle, and the ends of the filaments of the inner gill are attached to the foot or visceral mass. The fourth type of gill is far more highly [pg421] developed. The adjacent filaments are connected, not by cilia, but by vascular channels, and the depending and recurved portions of each filament are also connected in a manner presumed to admit of the passage of blood. This gives to the organ the appearance of basketwork or network. The ends of the filaments are attached to the mantle and to the visceral mass, as in the last order, forming cavities or chambers above (see Fig. C). This order includes the great majority of the Pelecypoda.

The fifth and last order is confined to but two rather obscure families, in which the gill-development is carried to the point of substitution of muscular partitions which form a separate chamber connected with the mantle cavity by a narrow slit, the surface of the chamber having respiratory functions (Fig. D).

The collector of living marine objects who has become fascinated by their beauty and who derives pleasure from examining the greater beauty of their structures will find a rich field for research in the pelecypod gills. But unless he has time at his disposal and some skill with a microscope, he would do well not to venture too far into this alluring but difficult and vexatious subject.

Our coastal waters are fairly rich in bivalves, but the most strikingly handsome species of this class—and there are many of them—are inhabitants of warmer seas. Of the great number of bivalves to be found upon our own shores we can only mention briefly some of the commonest species.

ORDER PROTOBRANCHIATA

In this family the gills are of the simplest and most primitive type. The mantle-edges are entirely open along the ventral margin, but they are united posteriorly in some of the Nuculidæ to form two short siphons. The palps are exceedingly large. The foot is also large, and by its disk-like surface is adapted to creeping, much as is a gasteropod foot; its edges are often crenulated or scalloped, and there is no trace of a byssus. The shells are [pg422] equivalve, and their most prominent feature is the hinge, which is beset with sharp, comb-like teeth in two straight rows, one upon each side of a central pit, a space reserved for the ligament.

Family SOLENOMYIDÆ

Two species of this genus, which are greatly prized by collectors on account of the extraordinary development of the epidermis of the shell, occur in New England waters. The strong corneous periostracum of a deep chestnut-color projects considerably beyond the margins of the valves; the shells are exceedingly thin and fragile, and are marked with radiating lines. The two species are easily distinguished by their difference in size. S. velum is about one inch long and one half of an inch high. S. borealis, of arctic range, is quite twice that size. Their anatomy is similar in essentials to that of Yoldia. These species live near shore in sandy bottoms, and are occasionally found upon the beach between tides. Chelsea Beach, just north of Boston, is an often-quoted locality.

ORDER FILIBRANCHIATA

There are several families of this order which are well represented in both the Atlantic and the Pacific waters of the United States. The characteristic feature of this group of bivalves is the filamentous gill, that is, a gill with the filaments long, doubled back, and united to each other only by ciliary junctures. These [pg424] junctures are so slight that they break readily when a specimen of a gill is handled, leaving the filaments free. The presence of a byssal gland in the foot, and often a well-developed byssus, is another characteristic of this order.

Family ANOMIIDÆ

This is a family of peculiar and highly specialized forms. Anomia has an irregularly rounded shell, with one convex and one flat or concave valve. There is no regular hinge or well-defined hinge-margin, but a raised fossette, or cartilage plate, occupies a position at the top of the valves. In the flat valve there is a large oblong hole just under the apex, through which projects a calcified byssus, by means of which the animal secures itself to oysters, dead shells, stones, or any solid object. The anomias, which have become stationary in habit, have practically lost their foot. The gills are very large and curved, while all the organs seem to be abnormally placed on account of the huge byssus and byssal muscle. For the byssus to pass, as it does, through a specially prepared hole in one of the valves is an extraordinary departure from the conventional types of byssiferous species. The heart is not traversed by the intestine. Altogether, then, Anomia is a very curious genus.

Family ARCIDÆ

The Arcidæ may always be distinguished by the long row of comb-like teeth upon the hinge, the total want of siphons (a fact which may be discovered in the shell alone by its lack of a pallial sinus), and the solid trapezoidal or round shell, with its tendency to strong ribs radiating from the umbones. The periostracum, or epidermis, is heavy and often velvety or even hairy. The animal of Arca has the gills placed in an oblique position; the foot is large and strongly developed. No trace of mantle fusion exists. The mantle-edges bear a row of composite eyes. The gill-filaments are entirely free, there being even no ciliary junctions.

Family MYTILIDÆ

The Mytilidæ are a large family, including the mussels, so commonly found between tides upon all shores. The two ordinary genera Mytilus and Modiola, which often occur associated together upon our eastern coast, may readily be distinguished one from the other by the position of their beaks. In the former genus the beak is terminal, that is, it is situated at the very tip-end of the shell; in the latter genus it is not quite terminal. Aside from this simple feature, the genera are practically the same, the animals being identical. Mytilus and Modiola, commonly known as mussels, have acquired the stationary habit and are provided with a relatively small foot (in some species amounting to no more than a mere tubercle); but in place of a useful foot is a well-developed byssogenous gland, which secretes an [pg427] exceedingly tough, fibrous byssus. By means of this the animal may not only attach itself firmly to any sort of object, but may actually move about. Fibers of the byssus are thrown out, and, as though possessed of life, they seize upon objects in the direction in which Mytilus desires to move, and by contraction of the muscles which control the byssus the animal is drawn forward, the operation being then repeated. It must be a very tedious method of travel. However, the Mytilidæ are not restless creatures. They pass their lives content to remain firmly fixed to some object, and their movements, if any, are within a very narrow circle. The animal has very long gills of the usual filamentous type. The mantle fuses at one point to form an anal siphon, the lower or branchial one being, therefore, functional. The palps are large. One curious feature of this group is the enormous extent of the genital glands, which actually appear to pervade the entire structure of the animal, gills, mantle, foot, and all. At times the whole being is a veritable receptacle for myriads of tiny yellowish eggs.

The Mytilidæ are of universal distribution, and are for the most part of littoral or shallow-water range. Some species are esteemed as an article of food, notably Mytilus edulis.

Mussel-culture has been profitably carried on in France for a long time, but the genus has not been utilized to any extent as food in this country. [pg428]

ORDER PSEUDOLAMELLIBRANCHIATA

This third order of Pelecypoda is made up of a number of families in which the gills are filamentous, but in which the filaments [pg430] have become united at their ends to the mantle (on the outer gills) and to the body-mass (on the inner gills). Here also the first traces of the higher type of gill found in the next order appear; that is, a gill in which the filaments are connected by vascular channels instead of by cilia. This order therefore is presumed to connect the true filamentous type of gill with the fully developed lamellar type. As the filaments do not always fuse with the mantle or foot, the description of the pseudolamellibranch gill becomes somewhat vague, and there is some room for doubt whether this order should exist at all.

Most of the genera placed in it are monomyarian; that is, they have but one adductor muscle, or if two, the anterior one is very small and unimportant. The mantle-edges are entirely open, there being no regularly formed siphons. As a rule, the foot is exceedingly small or quite aborted.

Family AVICULIDÆ

In this family there is an exception to the rule just stated: the foot is long. There is a byssus, and the gills (by their outer ascending filaments) are concrescent with the mantle.

The interior of all the Aviculidæ is of a highly polished nacre, and some of the larger species have been extensively collected for mother-of-pearl. To the Aviculidæ belong the pearl-oysters (Meleagrina margaritifera).

A delightful air of romance and adventure surrounds the pearl-fisheries, about which much has been written. The pearl is an abnormal product formed by the deposition of nacre around some foreign object, such as a grain of sand, or—usually, it is said—an egg which has failed to develop properly. They are seldom found in individuals having favorable conditions of growth, but those which are greatly crowded together and covered with various parasites and growths are most productive of them. The pearl is the same in substance as the nacreous shell of the pearl-oyster, and its iridescence is due to the fine striæ of the undulating layers of which it is composed. The pearl as well as the shell is produced by the shell-glands of the mantle. The value of the [pg431] pearl is based on the brilliancy of the nacre, the size, and the form. Luster, or "orient," is to the pearl what brilliancy is to the diamond. The round form has the greatest value, next the pear-shape, and lastly the oval. Pearls of inferior value are produced by other species than Meleagrina margaritifera, the true pearl-oyster. Many bivalves secrete similar bodies, but as they have the nature of the shell, those produced by mollusks having lusterless interiors are of no value. Beautiful pink pearls are found in the gasteropod Strombus gigas, the conch-shell of the West Indies. The shells of the pearl-oyster are themselves very valuable, being the "mother-of-pearl" used in the manufacture of buttons, knife-handles, inlay-work, and so on. They have three grades of commercial value; of the first are the "silver-lipped," from the South Seas, of the second the "black-lipped," from Manila and Ceylon, and of the third the "bullock-shells," from Panama.

Family OSTREIDÆ

This family probably interests more people than any other one in the class save Aviculidæ. The latter furnishes the pearl-oysters, the former the edible oysters, the two thus appealing to two very strong human cravings—those of vanity and hunger.

Few realize what an enormous business the oyster trade has become in the United States. The value of it is stated to be over thirteen million dollars annually, twenty-five million bushels of oysters being taken from the Chesapeake alone. The edibility of the oyster has been known from early times, for vast heaps of empty oyster-shells, known as kitchen-middens, occur in various parts of the world. Some of them are of such size and extent as to warrant the belief that their formation must have required centuries. Shell-mounds are found along the coasts of Florida and are of some archæological value. The cultivation of oysters as recorded by Pliny dates from the first century B.C., at which [pg433] time a Roman named Sergius Orata first cultivated oysters at Baiæ. The acuteness of the gastronomic sense of a Roman epicure is thus described by Juvenal:

The methods employed in oyster-farming resemble those of agriculture, in that the bed is prepared, seed is sown, superfluous and foreign growths are weeded out, enemies are driven off, and the crop is harvested at stated seasons. The oyster is ovoviviparous; that is, it retains its eggs until they are partly matured. These are held in the gills and mantle folds until the time of spawning, which begins in May and lasts through the summer months. The larvæ are ejected as ciliated spheres, called spat, and swim freely about for some time, often several days, before finding a resting-spot. The oyster-grower secures many of the larvæ by placing in their way substances to which they can attach themselves. The American culturist strews his carefully prepared beds with empty oyster-shells, on which the spat settle, and the seed is thus secured; for the spat, once fastened, lose the power of locomotion and become fixed. At the end of a year the shells which hold the young oysters (now about an inch long and called "fry") are taken up, and the fry are thinned out and replanted, or are sold to other oyster-farmers.

During the period of their growth the oysters are sometimes transplanted several times. At the end of three to five years they have attained marketable size, and the beds are then harvested and prepared for another crop. Some oystermen have several acres of bottom under cultivation. These areas are obtained by purchase or grant from the State, and their limits are as defined [pg434] as are the fenced-off acres of upland meadows. The business of the oyster-culturist is to plant the young oysters and watch their development, keeping the beds thinned, that the oysters may not be too crowded for their normal and symmetrical growth, and protecting them from their enemies, of which there are many. The principal enemies of the oyster are the starfish and the predaceous mollusks Urosalpinx and Nassa. Whole beds have been known to be destroyed in a single night by the visitations of starfishes, hence a constant watchfulness is required on the part of the oysterman. Policing the oyster-farms is another of his cares, for pirates abound, and a bed may be robbed in the night as easily as an orchard may be despoiled of its fruit. Oyster-culture is carried on extensively in Long Island Sound, on the coasts of New Jersey and Virginia, and in the Chesapeake Bay. The oysters from certain localities are esteemed more than others, the flavor of the oyster being very dependent upon the purity of the water and on the organisms upon which it feeds. It has been definitely shown that oysters grown in contaminated waters have been the agents of transmitting disease, notably typhoid fever and cholera.

Oyster-culture has reached the highest degree of perfection in France, where miles of muddy shores left by the ebb-tide are utilized for the purpose. The famous parc at Arcachon, covering ten thousand acres, illustrates the system generally practised. The spat is there collected on tiles coated with cement, piled in layers crosswise, and secured in crates. These tiles are exposed in favorable localities and collect the swimming embryos. The rough cement holding the spat is then chipped off the tiles and placed in wire trays. These ambulances, or caisses ostreophiles, placed between short posts, protect the fry from their enemies. At low tide the young oysters are carefully examined and sorted, and at the right age they are removed to open areas. The parc is divided into regular squares by canals of suitable width, some of the squares having banks and gates to retain the water of the receding tide if desired. Each man's parc is separated from that of his neighbor by canals of greater width, and often by stakes having a few branches on the ends. These [pg435] pignons, which sway in the wind, are said to frighten away the predaceous ray which is apt to hover about the preserves. The parcs are finally thinned out by sending the oysters to other parcs to be fattened. There is a celebrated parc d'élevage at Marennes. It is a collection of artificial ponds, the floors of which are covered with algæ, which harbor vast numbers of diatoms and other microscopic organisms on which the oysters feed. The green diatom (Navicula ostrearia) gives to the oysters of Marennes the green color and peculiar flavor which is so much esteemed by the epicures of France. To the American, however, the green oyster is not acceptable.

Family PECTINIDÆ

The scallop-shells (Pecten) are objects too familiar to require any general description. The rounded valve, usually ornamented with radiating ribs, and the wing-like projections (called "ears"), from each side of the umbonal region, are never-failing characters. The outline of Pecten has been considerably employed in conventional designs for mural decorations; indeed, the figure [pg436] of a well-known Mediterranean pecten (P. jacobius), found commonly in Palestine, became an emblem of religious significance during the middle ages. Returning crusaders fastened to their garments a specimen of "St. James's shell" as an evidence of the fact that they had been to the Holy Land, and the design of the shell came to be adopted upon many coats of arms and also in the insignia of various orders of devout and adventurous knights of the middle ages.

The animal is of the highest type of monomyarian mollusks, that is, of bivalve mollusks with only a single adductor muscle. Unlike most pelecypods, which have a very small foot, Pecten rarely has a byssus, and is neither a stationary nor a sluggish creature. It can propel itself through the water by spasmodically closing and opening its valves, in an eccentric, darting sort of flight, though most of the time it rests quietly upon the bottom. The mantle is entirely open and highly ornate about its margin, which is, furthermore, the seat of many eyes, capable, apparently, of no mean degree of vision. The adductor muscle is very large and strong, and occupies a central position, about which the gills circle; the latter are plainly filamentous.

ORDER EULAMELLIBRANCHIATA

With the pectens we leave behind all pelecypods with the true filamentous type of gill. In the order Eulamellibranchiata we find all the families to be possessed of the basketwork or crisscross branchial structure. Each gill is fundamentally formed of filaments which project downward, and then suddenly turn upon themselves and ascend; the ascending and descending limbs are connected, however, by processes of presumably vascular function, and adjacent filaments are connected by truly vascular channels. The closer connection of the filaments to form of each gill a sort of plate is further effected [pg439] by connective tissue, which sometimes is dense enough (though always porous) to obscure the reticulated appearance of the organ. Furthermore, the edge of the outer lamella of the outer gill unites with the mantle; likewise the edge of the inner lamella of the inner gill unites with the body-mass, and behind the body-mass with the gills upon the other side of the animal. This union of the four gills in a straight median line behind the foot and body-mass forms a septum, which divides off from the mantle cavity a "suprabranchial" cavity. Into this cavity the excreta are discharged, and with it the anal or excurrent siphon connects. The branchial or incurrent siphon thus pours its current of water into the lower mantle cavity, to bathe the gills and feed the mouth, while the fresh water is not contaminated by any open and wide connection with the excretory processes. In many of the forms where the siphons are very long and united, this septum, formed by the union of the dorsal edges of the inner gills back of the foot, is continued far into the siphons, constituting the division of the two into the anal and branchial siphons.

Another feature of this order is the marked tendency to mantle fusion. As there are always siphons, the mantle-edges must necessarily have fused at two points at least, in order to have formed the siphons. The tendency, however, is for the fusion to continue, narrowing the pedal opening more and more, as though the mantle were endeavoring to envelop the entire animal in a bag or sac open only at one end (siphonal opening), but yet slightly ripped along one seam (pedal opening).

This order includes the great majority of pelecypods, and admits of many very confusing modifications in its most essential features.

Family CARDITIDÆ

In this, the first family of the order, most of the characteristic features just spoken of are present. Mantle fusion, however, has not progressed beyond a degree which is just sufficient to form the siphons. There is a byssiferous gland. The name Carditidæ refers to the heart-shape of the shells. [pg440]

Family ASTARTIDÆ

Notwithstanding their rather small size, there is a trimness about the shells of Astarte which, taken together with their rich chestnut epidermis, makes them very interesting and desirable additions to the cabinet. The family is one of cold-water range, with a few representatives on the New England coast. Live specimens are not easily captured, for they live in deeper water than one would care to wade in, nevertheless they are frequently cast upon the beaches after storms. The animal has a very short efferent siphon, large labial palps, and very obliquely placed gills. Not more than twenty living species of Astarte are known, and all of them belong in, or are wanderers from, polar seas. Fully three hundred fossil species of this genus have been described from Mesozoic rocks in all parts of the world. The question naturally arises whether in these its dying days Astarte has sought colder waters in which to pass its remaining existence, or whether climates have changed. The fact that such strictly [pg441] tropical genera as Voluta and Conus are found fossil in northern Siberia seems to be evidence in proof of great climatic variations.

Family CYPRINIDÆ

This family is represented by one species upon the New England coast, which is much sought after by collectors. It is one of the larger clams, but is too uncommon to have received a popular name and to be generally well known by the fishermen along the shore.

Family LUCINIDÆ

This family finds its metropolis in warmer waters, and the best representatives of it must be sought for upon the Floridian beaches or in the shallow bays of that sandy coast. A long vermiform foot is a characteristic of the animal, as is also the fact that at times there is only a single gill upon each side of the body. In some of the Lucinidæ, more so than in most other pelecypods, the chief function of the gills is to furnish a brooding-place for the thousands of ova which the creatures generate. Sometimes a Lucina will be captured with the gills swollen out of all proportion, and literally stuffed with tiny, microscopic eggs. At such times the gills lose all semblance of branchial organs. The shells are orbicular, with depressed small umbones, a distinct lunule, a semi-external ligament, two cardinal teeth, and laterals (a variable feature). There is no pallial sinus. The color is white, and the outlines are rounded.

Family TELLINIDÆ

If we should create an aristocracy of beauty among the bivalves, as has been done by conchologists among the gasteropods, this family would deserve high rank. Most of the American species of Tellina are too small to impress one very greatly with their beauty, but in the West Indies and in the tropical Pacific waters are some wonderfully handsome shells belonging to this or to the allied genus Macoma. However, we have in Florida the very striking T. radiata, a truly beautiful shell, which, were it less common, would be highly prized in collections. Rarity, no doubt, adds a wonderful luster to shells as well as to gems. The [pg444] animal of Tellina has long, slender siphons, which are separate. The gills are small, and the outer lamella or branchial fold is directed dorsally. Although the foot shows evidences of a byssogenous gland, there is no actual byssus. The shells are porcelanous and translucent, equivalve, with an external ligament, and at least two cardinal teeth in each valve.

Family DONACIDÆ

The Donacidæ are represented upon our coasts by comparatively few species, all belonging to the genus Donax. The shells are under an inch in length, and have a peculiarly shortened anterior portion; thus they are inequilateral. Their ventral margins are finely denticulate. The pallial sinus is deep. There are two or three cardinal teeth and a variable number of laterals.

Family MACTRIDÆ

This is a very large family of universal distribution and with a great number of genera and subgenera, rather confusedly gathered into subfamilies. The dominant genus Mactra comprises the largest bivalve upon the east coast of the United States.

The mactras live in the sand near the margin of the water, often upon the exposed open coast. The mantle is open, except where it is fused to form the siphons. These are short and united. The outer gill is dorsally directed; that is to say, it does not depend into the mantle cavity as does the inner gill, but projects just the other way; it is also smaller than the inner one. The foot is strong, bent, and tongue-shaped, and no doubt well adapted to the rough life in the surf and the heavy, shifting sands. The main characteristic of the mactra shell is the prominent triangular-shaped fossette, or cartilage plate, situated internally and just under the beaks. The shells are equivalve, and devoid of bright colors or striking sculptural features. Internally the pallial line is plain, and the sinus well marked but not deep.

Family VENERIDÆ

In many respects this is the most distinguished pelecypod family. It is the largest in number of genera and species, is of world-wide distribution, and supplies to hungry man a number [pg448] of comestible species. Several of its genera have been named after various goddesses and nymphs on account of the great beauty of their shells. But from a purely biological point of view also the Veneridæ have claims to distinction, for they seem to represent about the highest type of shell-development among the bivalves. The test is extremely hard and often porcelanous. It is solid without being ponderous and unwieldy in the sense of causing the animal to be helplessly overburdened by the sheer weight of its shell. The valves are equal and have three stout cardinal teeth. The foot is strong, the animal is active, the siphons are free or partially united, and the gills are more or less crumpled and folded. There is a compactness and well-regulated arrangement of the organs in the Veneridæ, which impress one who has examined the anatomy of many pelecypods much as a well-built, efficient, and space-economizing machine would impress a mechanic. None of the organs are weak or crowded out to furnish room for the undue or awkward development of other organs. A good balance is preserved between them all, the result being a high type of pelecypod.

If we do not expect to find any of the more remarkable forms of the Veneridæ upon our shores we shall be the less disappointed when returning from collecting-expeditions. Nevertheless, there are a few species of Cytherea, Dosinia, and Tivela in North American waters which are very handsome shells; but those of our species which are included under the generic name Venus are in point of beauty not worthy of their promising name.

The coast of California is also favored by the Veneridæ, a number of large species belonging to several genera being present.

There are three species on the west coast. This genus is very closely allied to Venus, and is considered by many to be only a subgenus of the latter. All three species are white, solid, heavy shells which exhibit the same scheme of sculpturing, namely, numerous longitudinal ribs crossed by larger and less frequent concentric ridges.

This is a prominent genus of the Veneridæ. Its chief feature is the total want of lateral teeth. There are several large species in California.

Family PETRICOLIDÆ

Family CARDIIDÆ

This is another important family of the Pelecypoda, which, with the Veneridæ, the Mactridæ, and the Tellinidæ, is entitled to distinction on account of its high organization, its high type of shell, its universal geographical distribution, and its great beauty. The dominant genus is Cardium—a name given on account of the fact that the shell is shaped like a heart. The animal has a very long, recurved, and surprisingly strong foot. The mantle-edges are quite freely open to the siphonal region and are highly papillate and waved. The siphons are usually very short, but have wide exterior openings and are also strongly papillate about their margins. The gills are obliquely situated, and seem to be thicker and heavier than is usual in pelecypods; they are much folded, the outer lamella being the smaller. With such a pointed foot and such short siphons Cardium is obviously not a deep-burrowing genus; but it does partially bury itself in soft semi-liquid sand. Its progression is effected by leaps which it is enabled to make by reaching far out with its foot, then suddenly twisting to one side and throwing the shell several inches. The shell is ventricose, is closed or gapes slightly posteriorly, and has prominent subcentral umbones and an external ligament. The sculpture-scheme of Cardium (if the shell is not perfectly smooth) is one of radiating ribs or ridges, which, being regular, form a perfect crenulation of the ventral margin. There are two cardinal teeth in the center, and one lateral tooth upon both the anterior and the posterior side: the latter are situated at some little distance from the beaks.

Family MYIDÆ

In this family we encounter, rather suddenly, some new features not heretofore seen in the pelecypod structure. In the first place, the siphons are enormously large, are united, and are surrounded by a leathery epidermis. The mantle-edges are fused together along the entire ventral margin, except for a small slit through which the foot may project. Although the animal may withdraw the long siphons into its shell, yet they remain to a certain extent exposed, for the valves gape widely posteriorly, and only slightly less so anteriorly. In the economy of these forms the shell seems to play a less important part than it does in the Veneridæ, in the Tellinidæ, and generally in those families whose shells are strong and, closing firmly, afford the animal within a real protection. The shell of Mya (the principal genus) is thin, white, and of a softer chalky texture; it gapes widely "fore and aft," and has a loosely constructed hinge apparatus, consisting of an erect projecting tooth, which fits into a pit in the opposite valve.

Family SOLENIDÆ

In this family are included the long, slender bivalves commonly known as "razor-shells." Every one who has been to the sea-shore has become familiar with these odd-looking mollusks, for their valves are always to be found upon every beach. Their station is upon sandy flats or bars more or less exposed at low tide. They burrow into the sand perpendicularly to a depth of two or three feet, remaining hidden most of the time. Occasionally a colony of them will be seen, each one projecting slightly from his burrow. If approached most cautiously some of them may be captured, but if the sand is jarred they all take fright and disappear in an instant. It is no easy matter to capture a "razor" when once he has taken warning, for he will dig down into the sand about as fast as one can follow with a spade. A good way to catch one is to approach his burrow carefully, and then plunge a spade obliquely down below him, thereby [pg458] cutting off his retreat. So tenaciously will they cling to the sand by expanding the muscular foot that the shell may be pulled entirely off the body before they will let go.

Family GLYCIMERIDÆ

Family PHOLADIDÆ

There is a striking resemblance between the shells of this rock-boring family and those of the petricolas—a resemblance which consists principally in the texture of the shell and the tendency to different types of sculpturing upon the posterior and anterior surfaces of the valves.

In Pholas the anterior part of the hinge-margin is reflected back over the umbones, and a long rib-like tooth springs from under the umbonal region and curves out almost to the center of the valves. The shell gapes "fore and aft," and is thin, white, very hard, and brittle. The animal has a short, truncated foot and a small orifice in the mantle through which the foot may be projected. The siphons are long and are united almost to their ends. Dorsally, an exposed portion of the animal is protected by accessory calcareous plates. The habits of Pholas are very interesting. It is found in holes gouged out of solid rock or out of pieces of wood; sometimes, like Petricola, it may be found excavating in hard clay. As the anterior end of a Pholas shell is the larger in diameter, and is the end which is most deeply buried in the rock (the opening of the burrow being comparatively small), there was some mystery as to the way in which the creature manages to get inside its rocky dwelling. Observations in aquaria have shown that the young Pholas begins his process of home-building very early in life. The wearing away of the stone is effected by constantly turning the shell around, scraping with the anterior edges of the valves. A lodging-place having been secured, Pholas is obliged to work constantly to enlarge his burrow for the accommodation of his growing shell. The long siphons may project from the hole and draw in food and breath, but the animal is a prisoner for life. When Pholas has withdrawn his long siphons he is reasonably secure from his enemies, but [pg461] nevertheless thousands of them are destroyed by predatory starfishes, who know how to get at their victims. The restless crustaceans, ever on the outlook for a meal, often nip the siphons of the rock-dwellers, and a kind of worm sometimes attacks them, and, destroying the animal, proceeds to occupy the empty shell and burrow.

Family TEREDINIDÆ

Family PANDORIDÆ

CLASS CEPHALOPODA

The Cephalopoda form a singularly isolated group, and are so superior in organization and intelligence to all other mollusks that it is difficult to believe that they are first cousins to the lethargic gasteropod and the simply constructed bivalve. But the class bears the stamp of its origin in a mantle, a radula, and a disposition of internal organs and functions which, although highly perfected, is essentially molluscan.

Along the Atlantic coast of the United States, particularly in its northern portion, occur several examples of cephalopods belonging to the genera Ommastrephes and Loligo, all the species of which are referred to, in common parlance, as "squids." They frequent shallow water, and are often to be found in weirs, darting about with rapid, spasmodic movements, or perhaps lying motionless on the bottom. The squids enter the weirs for the purpose of capturing the young mackerel which are caught in these traps. The squid lies quietly upon the bottom, which it simulates so closely in color as to be almost invisible, and when [pg465] a school of fishes swims over it, darts suddenly into the midst of it, seizes a fish with its sucker-bearing arms, and kills it by the bite of its parrot-like beak or jaws. Sometimes it happens that squids, while pursuing fish too near shore, precipitate themselves upon the beach, where they flounder about, ejecting water from their siphons, which pushes them only farther away from the water, and squirting out "ink" from their ink-sacs in a vain endeavor to hide themselves from view. On bright moonlight nights squids often go ashore in vast numbers, and perish within a few inches of their native element, which they seem to be unable to regain. These creatures usually swim backward, and the theory is that, dazzled by the bright light of the moon, they continue to gaze at it while swimming, and if there happens to be a shore in the direction of their movements, they suddenly find themselves beached. The fishermen of Canada and New England take advantage of this habit and capture great quantities of squids by placing bright lights in the bows of their boats and then rowing toward shore, thus driving the squids out of the water. The Banks fishermen use them as bait for catching cod. The right claimed by American fishing-schooners to purchase squids in Newfoundland has helped to keep alive the quarrel between Canadian and American fishermen, which has vexed their respective governments for many years.

The range in size among the species of this class is very remarkable. The little sepiolas are about an inch long; the squids of our coasts vary in length from eight inches to one foot; and the giant Architeuthis of the North Atlantic measures, often, fifty feet from the end of its arms to the tip of its tail. Such a creature, with its long arms provided with suckers, its powerful jaws, and its rapid, alert movements, is a formidable foe. These animals have been the basis of many legends about sea-serpents and sea-monsters. A gruesome story of an octopus is told by Victor Hugo in "The Toilers of the Sea," where he gives a thrilling account of a man's encounter with a devil-fish in a cave. One who has read this tale has a vivid picture in his mind of the giant squid, and the danger of meeting one of these many-armed foes. Victor Hugo's devil-fish, [pg466] however, is an animal not true to nature, but a composite, having the attributes of the polyp and of the octopus, and the name of a large ray of Southern waters, a real fish, the Cephaloptera, known in its localities as devil-fish. This monstrosity of the novelist's imagination has, however, done more to acquaint the general public with these interesting cephalopods than have the descriptions of scientists.

The giant squid, which is such a dangerous foe, has its own enemy in the sperm-whale. The cachalot swims through the water with its lower jaw hanging, the cephalopod grasps the jaw, and the whale then shuts his capacious mouth upon it. Whalemen describe conflicts between these enormous creatures, the whale always being the conqueror. Sperm-whales killed by man often eject great quantities of the squids in their death throes, showing this food to be almost their exclusive diet.

The name "cephalopod," meaning "feet around the head," is descriptive in part of their anatomy. The head is usually marked off by a neck-constriction, and it bears two highly organized eyes. The foot is fused in part with the head above the eyes and around the mouth; on the upper side it is divided into eight or ten long arm-like processes, bearing suckers, which act as organs of prehension. The under part of the foot forms a tube called the funnel. Through the funnel the animal expels water from the mantle cavity, and thus propels itself through the water.

The mantle covers the body of the animal, and is a cup-shaped or conical envelope, open only at the anterior end, through which project the head and siphon or funnel. It is attached to the body by a line on the dorsal side, the anterior margin being free and open, but provided with an arrangement of cartilages by which it can be hooked on to the siphon, thus completely closing the entrance to the mantle cavity. The mantle is very muscular, and is constantly expanding and contracting, taking water into the mantle cavity through the mantle opening for respiratory purposes, or expelling it through the siphon for propulsion; in the latter case the mantle opening is closed at the moment of ejecting the water. When the siphon is in its normal position [pg467] the animal swims backward; but it can be turned back over the edge of the mantle, giving a forward movement.

The surface of the mantle is covered with pigment-cells (chromatophores). There are sets of chromatophores containing different colors. The cells are opened or closed at will by muscular action of their walls. When open the cells seem to fuse together, giving a solid color-surface, or spots of color as desired, in blue, red, yellow, or brown; when closed they seem as specks on the almost transparent tissues of the animal. Flashes of changing color follow one another with great rapidity over the living animal. In swimming it assumes the color of its surroundings.

Another curious means of protection possessed by the dibranchiate cephalopods is an ink-bag, the brown or black secretions of which are ejected through the siphon, clouding the water when the animal wishes to escape from danger. The ink taken from the ink-sac of Sepia is an article of commerce.

Only Nautilus and the female Argonauta have the characteristic external shell of mollusks. In all other forms the shell is internal or is invested in the integument of the mantle. Of such is the cuttlebone of commerce, which is a calcareous leaf-like body obtained from Sepia, the cuttlefish. The common squid Loligo has a horny substance situated in the dorsal side of the mantle, called the pen. Spirula has a spiral internal shell divided into chambers. Vast numbers of these shells are cast upon the beaches of the Pacific Islands, and they have also been found on the shore of Nantucket.

Cephalopods are separated into two subclasses. In the first, the Tetrabranchiata, there are four branchiæ, four nephridia, and four auricles. They are without an ink-sac, and have the foot divided into lobes bearing sheathed tentacles. Nautilus is the only genus.

SUBCLASS TETRABRANCHIATA

Probably the best-known cephalopod is Nautilus—the pearly-shelled, chambered nautilus made immortal in the beautiful poem of Oliver Wendell Holmes. The shell of Nautilus is a flat spiral; the interior is divided by septa forming a series of chambers; [pg468] the septa are perforated, and through the opening runs a tube or prolongation of the body, the siphuncle, which extends to the tip of the shell. The chambers are filled with gas. The animal in the course of its growth moves forward into a newly formed chamber and builds a new septum, closing the cavity last occupied. Nautilus lives among the coral reefs of the southern Pacific. Its four or five species are the remnants of a once very extensive race of cephalopods. The fossil remains of many species of Nautilus, together with various other genera of shell-bearing cephalopods, indicate that this group has seen its best days. The dibranchiate genera, however, appear to have reached their maximum at the present day.

SUBCLASS DIBRANCHIATA

The second subclass, the Dibranchiata, is characterized by two branchiæ and two auricles. The main part of the foot is divided into eight or ten long arms provided with numerous suckers arranged in from one to four rows on the ventral side of the arms. They have also an ink-sac. The Dibranchiata are divided into two orders: the Octopoda, which have eight arms, and comprise the Octopus and Argonauta; and the Decapoda, which have ten arms, and comprise Spirula, Ommastrephes, Sepia, and Loligo. In these animals two of the ten arms are longer than the others, and these tentacular arms have suckers only on their broadened, club-like ends, they are kept retracted within grooves, one on each side of the head, except when needed for prehension. [pg469]

CHORDATA
CLASS UROCHORDA or TUNICATA

The most conspicuous animals of this class are the ascidians, which are common objects on rocky coasts. The simple ascidians are peculiar leathery, sac-shaped bodies which send out jets of water when touched. This habit gives them the common name of "sea-squirts." Some are highly colored, especially those of Southern waters; others are somber, unattractive bodies, often growing in masses. The compound ascidians are gelatinous colonies, sometimes forming thin incrustations, sometimes jelly-like masses, on seaweeds, shells, etc. This class comprises also the beautiful Salpa, a genus of free-swimming animals having transparent bodies encircled by rings of muscular bands, and in one stage forming chains of attached organisms which swim on the surface of the sea and of bays.

The tunicates are by some authors classed with the vertebrate animals because in the larval stage they have a notochord; this disappears, however, in the adult form, and the animals are considered degenerates. The tunicates are interesting to biologists from the remarkable changes they undergo in their life-history, and (in some genera) the marked phase of alternation of generation. One of their curious anatomical features is the blood-vascular system. The circulation is propelled by wave-like contractions of the heart, which, after forcing the blood one way for a time, stops and reverses the blood-current. The tunicates are widely distributed, and occur at all depths. (Plate LXXXV.) [pg475]

The animals of this genus are transparent, subcylindrical, smooth, gelatinous bodies encircled by bands of white muscular fiber. They strikingly exemplify alternation of generations. They occur in two distinct conditions, one being solitary, the other consisting of animals united in chains. The solitary individuals are about an inch long, and have two long processes at the posterior end. These single animals reproduce by budding, and form series of individuals in small chains, the animals being arranged in two rows. The chains grow to the length of a foot or more, and contain twenty to thirty pairs of salpas. Each of these connected individuals produces in turn a single egg, which becomes a single Salpa, and this again, like its grandmother, reproduces by budding. Thus the animals are alike only in alternate generations. The naturalist Chamisso, who discovered the relationship between the two forms, expressed it as follows: a Salpa mother is not like its daughter or its mother, but resembles its sister, its grandmother, and its granddaughter. The single zoöids liberate many colonies during the summer, which grow rapidly, and in the autumn the chains are exceedingly abundant. The Salpa chains swim about with a serpentine movement, and are beautiful, delicate objects with their transparent bodies banded with white, tinged with pink, and streaked with blue.

SIMPLE ASCIDIANS

These are solitary and usually fixed; they are never free-swimming, and when in colonies each animal has a distinct test. All the larger ascidians, or sea-squirts, belong to this group.

Body more or less globular, membranous, attached or free; orifices on very contractile tubes.

The animal is attached, the body coriaceous, and the orifices four-lobed. Frequently associated in groups, the individuals often differing in color.

Test gelatinous or cartilaginous; attached; it grows in bunches under stones at low-water mark. Sometimes it is variously [pg477] colored, but otherwise it is repulsive in aspect. The apertures are wide apart; one orifice is eight-lobed, the other six-lobed.

COMPOUND ASCIDIANS

Ascidians of this group form fixed colonies, and are embedded in gelatinous material, the animals having a common test, but not being united by any internal union. The colonies thus formed are flat and incrusting, or are branched and lobed, or sometimes elevated on stalks. The zoöids are in some cases dotted irregularly over the entire surface, in others are in rows, or again are in groups. They have various colors—purple, yellow, blue, gray, and green. They are common on eel-grass, the piles of wharves, the bottoms of boats, and so on.

INDEX

Heavy-faced type is used to indicate names of classes, orders, genera, etc.; heavy-faced numerals to indicate the place where the fullest description is given

A
Abdomen, 243, 246.
Abductor muscles, 302.
Aboral, 202.
- Surface, 201.
Abyssal, 23.
Acalephs, 134.
Acanthalithodes, 240, 271.
- A. hispidus, 240, 271.
Acephala, 409.
Acetabularia, 51, 57.
- A. crenulata, 51, 57.
Acmæa, 9, 309, 312.
- A. mitra, 324, 357.
- A. patina, 324, 357.
- A. testudinalis, 41, 42, 324, 343, 348, 356.
- A. testudinalis, var. alveus, 324, 357.
Acmæidæ, 324, 356.
Acontia, 145.
Acorn-shell, 254.
Actiniaria, 141, 142, 143, 144.
Actinozoa, 112, 115, 141, 142.
Adamsia palliata, 144, 267.
Adductor muscles, 302, 413, 417.
Æolididæ, 324.
Æolis, 41, 42, 309, 324, 354.
- Æ. papillosa, 324, 354.
Æquoreidæ, 116, 128.
Ætea, 188, 194.
- Æ. anguinea, 188, 194.
Agarum, 36, 42, 63, 68, 69.
Aglaophemia, 127.
- A. struthioides, 116, 127.
Ahnfeldtia, 76, 82.
- A. plicata, 76, 82.
Alaria, 63, 69.
- A. esculenta, 41, 42, 63, 69.
Albunæa, 240, 269.
- A. gibbesii, 240, 269.
Alcyonacea, 141, 151.
Alcyonaria, 141, 142, 150, 152.
Alcyonidium, 189, 192, 197.
- A. hirsutum, 189, 197.
- A. hispidum, 189, 198.
- A. parasiticum, 189, 198.
- A. ramosum, 189, 197.
Alcyonium, 141, 151.
- A. palmatum, 141, 150, 161.
Aleutian province, 311.
Algæ, 25, 48, 62, 76.
- Botanical facts about, 25.
Alternation of generation, 120, 121.
Amarœcium, 473, 477.
- A. pellucidum, 473, 477.
Ambulacra, 201, 202, 205, 214, 218.
Ambulacral groove, 205.
- Ossicles, 205.
- Zones, 201, 202, 205, 218, 229.
American division, 24.
Amphictenidæ, 162, 183.
Amphineura, 300, 316, 317, 320, 321, 323.
Amphipoda, 242, 289.
Amphissa, 312.
- A. corrugata, 326, 389.
Amphitrite, 161, 182.
- A. ornata, 161, 182.
Amphiura, 213, 215.
- A. squamata, 213, 215.
Ampullæ, 201, 205, 206, 218.
Anadyomene, 51, 57.
- A. flabellata, 51, 57.
Anatomy, 20.
- Of higher Crustacea, 246.
Anemone Cave, 40.
Angel's-wings, 461.
Animal-flowers, 142.
Animal life in its lowest forms, 21.
Annelida, 305.
Annulata, 159, 161, 164, 170.
Anomia, 405, 424.
- A. aculeata, 405, 425.
- A. lampe, 405, 425.
- A. simplex, 405, 424.
Anomiidæ, 405, 424.
Anomura, 240, 264.
Antennæ, 243, 246, 258.
Antennules, 243, 246, 258.
Antheneidæ, 204, 209.
Anthomedusæ, 116.
Aperture, 302.
Apex, 343.
Aphrodite, 161, 174.
- A. aculeata, 161, 174.
Aphroditidæ, 161, 172, 173.
Aplacophora, 300, 321, 323.
Aplysella violacea, 105.
Aplysia Wilcoxii, 352.
Aplysiidæ, 324.
Apoda, 228, 233.
Appendicularia, 472.
Arabella, 161, 179.
- A. opalina, 161, 179.
Arbacia, 217, 222.
- A. punctulata, 217, 222.
Arbaciadæ, 217, 222.
Arca, 310, 405, 425.
- A. noæ, 405, 426.
- A. pexata, 405, 425.
- A. ponderosa, 405, 426.
Arcachon, 434.
Architeuthis, 465.
Arcidæ, 405, 425.
Arctic province, 309.
Arctica, 406, 441.
- A. islandica, 406, 441.
Arenicola, 162, 172, 184.
- A. marina, 162, 184.
Arenicolidæ, 162, 184.
Argonauta, 464, 467, 468.
- A. argo, 464, 469.
Aristocratic genera, 313, 377, 398, 401.
Aristotle's lantern, 203.
Arthrocladia, 62, 67.
- A. villosa, 62, 67.
Arthropoda, 238, 244.
Arthrostraca, 242, 289.
Articulata, 188.
Ascidia, 473, 476.
- A. amphora, 473, 477.
- A. callosa, 473, 477.
- A. compositæ, 473.
- A. simplices, 473.
Ascidiacea, 473.
Ascidians, 8, 474.
- Compound, 474, 477.
- Simple, 474, 475.
Ascophyllum, 63, 73.
- A. nodosum, 43, 63, 73.
Asperococcus, 62, 66.
- A. echinatus, 62, 66.
Astacoidæ, 240, 261.
Astarte, 309, 406, 440.
- A. castanea, 406, 441.
- A. undata, 406, 441.
Astartidæ, 406, 440.
Asterias, 204, 212.
- A. Forbesii, 204, 207, 212.
- A. gigantea, 204, 207, 212.
- A. ochracea, 204, 212.
- A. vulgaris, 43, 204, 207, 212.
Asteriidæ, 204, 212.
Asterina, 204, 210.
- A. folium, 204, 210.
- A. miniata, 204, 211.
Asterinidæ, 204, 210.
Asteroidea, 200, 204, 205.
Astræa, 141, 146, 147, 148.
Astrangia, 141, 150.
- A. danaë, 13, 141, 150.
Astropecten, 204, 209.
- A. articularis, 204, 209.
Astropectinidæ, 204, 208.
Astrophyton, 213, 215.
- A. Agassizii, 213, 215.
Astyris gausapata, 326, 389.
Asymmetrical, 328.
Aurelia, 133, 137.
- A. flavidula, 133, 137.
Auricula, 231.
Auriculata, 201.
Avicula, 405, 431.
- A. atlantica, 405, 431.
Avicularia, 190, 193.
Aviculidæ, 405, 430.
B
Balanus, 239, 250, 254.
- B. balanoides, 239, 255.
- B. crenatus, 256.
- B. eburneus, 239, 255.
- B. geniculatus, 239, 256.
- B. ovularis, 255.
- B. rugosus, 239, 256.
- B. tintinnabulum, 239, 256.
Bangia, 78, 96.
- B. fusco-purpurea, 43, 78, 96.
Bangiaceæ, 78, 96.
Barnacles, 8, 43, 245, 250.
Bathymetrical division, 23.
Bdelloura, 160, 167.
- B. Candida, 160, 167.
- B. rustica, 160, 167.
Beach-flea, 245, 289.
Beak, 417.
Bela, 309.
Benthos, 23.
Beroïda, 154, 157.
Bilateral symmetry, 20, 302, 320, 321.
Binomial nomenclature, 28.
Bipinnaria, 201.
Biramous, 243, 257.
Bittium, 326, 374.
- B. nigrum, 326.
Bivalves, 306, 307, 314, 315, 409.
- Mud-boring, 452.
- Rock-boring, 452, 460.
Blastostyles, 120.
Blue crab, 275.
Blue-green seaweeds, 47, 48, 49.
Body-whorl, 304, 343.
Bolina, 154, 156.
- B. alata, 154, 156.
- B. septentrionalis, 154, 156.
- B. vitrea, 154, 156.
Boltenia, 473, 476.
- B. clavata, 473, 476.
Bopyridæ, 292.
Boreal, 23.
Boring amphipod, 290.
Boring-sponges, 105.
Bostrychia, 77, 89.
- B. rivularis, 77, 89.
Botanical facts about algæ, 25.
Botryllus, 473, 477.
- B. gouldii, 473, 477.
Bougainvillea, 124.
- B. superciliaris, 116, 124.
Box-crab, 287.
Brachyura, 241, 258, 272.
Brain-corals, 146.
Branchiæ, 302, 319, 329, 336, 413.
- Dermal, 208.
Branchiolaria, 201.
Brissopsis, 217, 227.
- B. lyrifera, 217, 227.
"Brit," 249.
Brittle-stars, 43, 200, 214.
Brown bodies, 190, 193.
Bryopsis, 51, 59.
- B. plumosa, 51, 59.
Bryozoa, 191.
Buccal mass, 302, 317.
Buccinidæ, 327, 391.
Buccinum, 12, 309, 313, 327, 330, 392.
- B. undatum, 42, 44, 314, 327, 331, 392.
Bucidium parasiticum, 144.
Bugula, 188, 192, 193, 195.
- B. flabellata, 188, 196.
- B. Murrayana, 188, 196.
- B. turrita, 43, 188, 195.
Bulla, 324, 351.
- B. nebulosa, 324, 351.
- B. occidentalis, 324, 351.
- B. solitaria, 324.
Bullidæ, 324.
Butterfly-shells, 323.
Byssus, 415, 426, 432.
C
Caberea, 188, 195.
- C. Ellisii, 188, 195.
Cake-urchins, 218, 224.
Calappa, 241, 287.
- C. flamma, 241, 287.
Calappidæ, 241, 287.
Calcarea, 100, 104, 106.
Calcareous hydroids, 129.
- Seaweeds, 31, 147.
Californian province, 312.
Callinectes, 241, 275.
- C. hastatus, 12, 275.
- C. sapidus, 241, 274, 275.
Calliostoma, 312, 325, 361.
- C. annulatum, 325, 361.
- C. canaliculatum, 325, 361.
- C. costatum, 325, 361.
- C. jujubinum, 325, 361.
- C. occidentale, 325, 361.
Callista, 311, 410.
- C. gigantea, 450.
- C. maculata, 450.
Callithamnion, 15, 78, 79, 90.
- C. americanum, 78, 90.
- C. Baileyi, 78, 91.
- C. byssoideum, 78, 91.
- C. floccosum, 78, 91.
- C. Pylaisæi, 78, 91.
- C. seirospermum, 78, 91.
Callophyllis, 76, 82.
- C. laciniata, 76, 82.
- C. variegata, 76, 82.
Calothrix, 48, 49.
Cameo-cutting, 381.
Campanularians, 116, 121, 125.
Canal, 302.
- Anterior, 344.
- Posterior, 344.
- System of sponge, 103.
Cancellaria, 310, 327, 402.
- C. reticulata, 327, 402.
Cancellariidæ, 327, 402.
Cancellus, 266.
Cancer, 241, 277.
- C. antennarius, 241, 280.
- C. borealis, 241, 277.
- C. irroratus, 241, 277.
- C. magister, 241, 278.
- C. productus, 241, 278.
Cancroidæ, 241, 277.
Caprella, 8, 242, 291.
- C. geometrica, 242, 291.
Capulidæ, 325, 369.
Carapace, 243, 246.
Carcinides, 241, 274.
- C. mænas, 241, 274.
Carcinus mænas, 41, 274.
Cardiidæ, 407, 453.
Cardita, 406, 440.
- C. borealis, 406, 440.
- C. floridana, 406, 440.
Carditidæ, 406, 439.
Cardium, 310, 311, 407, 410, 413, 453.
- C. corbis, 407, 454.
- C. elatum, 407, 454.
- C. islandicum, 407, 454.
- C. isocardia, 407, 454.
- C. lævigatum, 407, 454.
- C. magnum, 407, 453.
- C. mortoni, 407, 454.
- C. pinnulatum, 407, 454.
- C. quadrigenarium, 407, 454.
- C. serratum, 407, 454.
- C. substriatum, 407, 454.
Caribbean province, 310.
Carinated, 302.
Cartilage, 417.
Cartilaginous, 27.
Cassididæ, 326, 380.
Cassiopeia, 133, 140.
- C. frondosa, 133, 140.
Cassis, 310, 326, 380.
- C. cameo, 326, 380.
- C. inflata, 326, 381.
- C. Madagascarensis, 381.
- C. testiculus, 326, 381.
- C. tuberosa, 326, 380.
Caudina, 228, 233.
- C. arenata, 228, 233.
Caulerpa, 51, 56, 59.
- C. Mexicana, 51, 60.
- C. paspaloides, Plate VIII.
- C. plumaris, Plate VIII.
- C. plumosa, 51.
- C. prolifera, 51, 60.
- C. Wurdemanii, 51.
Caulerpaceæ, 51, 59.
Cellepora, 188, 197.
- C. pumicosa, 188, 197.
- C. ramulosa, 188, 197.
- C. scabra, 188, 197.
Cellularia, 188, 195.
- C. ternata, 188, 195.
Cellularina, 188.
Cenobita, 240, 268.
- C. diogenes, 240, 268.
Cenobitidæ, 240, 268.
Cephalic, 243, 246.
Cephalopoda, 301, 315, 320, 321, 464.
Cephalothorax, 243, 246, 272.
Ceramieæ, 78, 90.
Ceramium, 27, 43, 78, 92.
- C. diaphanum, 78, 93.
- C. fastigiatum, 78, 93.
- C. rubrum, 78, 92.
- C. rubrum, var. proliferum, 78, 93.
- C. rubrum, var. secundatum, 78, 93.
- C. strictum, 78, 93.
- C. tenuissimum, 78, 93.
- C. tenuissimum, var. patentissimum, 78, 93.
Cerata, 353.
Cerebratulus, 160, 170.
- C. angulatus, 160, 170.
Cerianthus, 144.
Cerithidea, 326, 375.
- C. sacrata, 326, 375.
- C. scalariformis, 326, 375.
Cerithiidæ, 326, 373.
Cerithium, 326, 374.
- C. floridanum, 326, 374.
- C. minimum, 326, 374.
- C. muscarum, 326, 374.
Cerostoma, 326, 385, 387.
- C. foliatum, 326, 385.
- C. nuttallii, 326, 385.
Cestida, 154, 157.
Cestoda, 160.
Cestum, 154, 157.
- C. veneris, 154, 157.
Cetochilus, 239, 249.
Chætæ, 173.
Chætangieæ, 76, 80.
Chætobranchus, 161, 182.
- C. sanguineus, 161, 182.
Chætomorpha, 51, 53.
- C. ærea, 51, 53.
- C. linum, 51, 54.
- C. melagonium, 51, 53.
- C. picquotiana, 54.
- C. tortuosa, 53.
Chætopoda, 161, 171.
Chalinopsilla, 100, 107.
- C. arbuscula, 100, 107.
- C. oculata, 100, 107.
Chamædoris, 51, 56.
- C. annulata, 51, 56.
Champia, 77, 85.
- C. parvula, 77, 85.
Charybdæa, 133, 137.
- C. marsupialis, 133, 137.
Cheilostomata, 188, 194.
Chelæ, 243, 258.
Cheliped, 243, 258.
Chelura, 242, 290.
- C. terebrans, 13, 242, 290.
Chicoreus rufus, 382.
Chione, 406, 451.
- C. fluctifraga, 406, 451.
- C. simillima, 406, 451.
- C. succincta, 406, 451.
Chiridotea, 242, 294.
- C. cæca, 242, 294.
- C. entomon, 242, 294.
Chiton, 9, 309, 322.
- C. albus, 323.
- C. apiculatus, 323.
- C. ruber, 41, 323.
- C. spinosus, 322.
Chitonidæ, 312, 322.
Chlorophyceæ, 28, 47, 51.
Chlorostoma, 312, 325, 362.
- C. brunneum, 325, 362.
- C. funebrale, 325, 362.
Choanocytes, 102.
Choanoflagellata, 102.
Chondria, 77, 90.
- C. dasyphylla, 77, 90.
- C. striolata, 77, 90.
- C. tenuissima, 77, 90.
Chondrospongiæ, 100.
Chondrus, 76, 80.
- C. crispus, 38, 76, 80.
Chorda, 63, 68, 69.
- C. filum, 63, 69.
Chordaria, 62, 67.
- C. flagelliformis, 43, 44, 62, 67.
Chordariaceæ, 62, 67.
Chordata, 19, 472, 474.
Chorus, 312, 326, 388.
- C. belcheri, 326, 388.
Chromatophores, 467.
Chrysodomus, 12, 309, 313, 327, 392.
- C. decemcostatus, 327, 392.
Chylocladia, 77, 85.
- C. articulata, 77, 85.
Cidaridæ, 217, 222.
Cidaris, 217, 222.
- C. tribuloides, 217, 222.
Ciliary flames, 164.
Cinereous, 302.
Cirolana, 242, 292.
- C. concharum, 242, 292.
Cirratulidæ, 161, 181.
Cirratulus, 161, 181.
- C. grandis, 161, 181.
Cirri, 172, 302.
Cirripedia, 239, 250.
Cirripeds, 251.
Cistenides, 162, 183.
- C. Gouldii, 162, 183.
Cladocera, 238.
Cladophora, 26, 51, 54.
- C. arcta, 51, 54.
- C. gracilis, 51, 54.
- C. rupestris, 51, 54.
Cladostephus, 62, 65.
- C. verticillatus, 62, 65.
Clam, 321, 448.
- Giant, 447.
- Hard-shell, 448, 451, 456.
- Little Neck, 410, 448.
- Soft-shell, 456.
- Worms, 176.
Classification, 19.
- Of gasteropods, 348.
- Of mollusks, 320.
Clava, 122.
- C. leptostyla, 116, 122.
Clibanarius, 240, 267.
- C. vittatus, 240, 267.
Cliona, 100, 106.
- C. sulphurea, 100, 105, 106.
Cloaca, 229.
Clymenella, 162, 183.
- C. torquata, 162, 183.
Clypeaster, 217, 224.
- C. ravenellii, 217, 224.
Clypeastroidea, 217, 224.
Clytia, 126.
- C. bicophora, 116, 126.
- C. poterium, 116, 126.
Cockles, 453.
Codiaceæ, 51, 59.
Codium, 51, 59.
- C. tomentosum, 51, 59.
Cœlenterata, 111, 112, 113.
Cœlopleurus, 217, 222.
- C. floridanus, 217, 222.
Cœnosarc, 118.
Coffee-shells, 379.
Collecting, 6.
- And preserving seaweeds, 15.
- At Bar Harbor, 40.
Columbella, 326, 388.
- C. avara, 326, 389.
- C. corrugata, 326, 389.
- C. gausapata, 326, 389.
- C. lunata, 326, 389.
- C. mercatoria, 326, 388.
- C. similis, 326, 389.
Columbellidæ, 326, 388.
Columella, 302, 344.
Comatula, 234, 235.
Comb-jellies, 112, 115, 155.
Communal life, 121.
Conceptacles, 72.
Conchs, 377.
Conch-shell, 376.
Concrescent, 302.
Confervaceæ, 26, 51, 53.
Conidæ, 327, 401.
Connostomæ, 133.
Conus, 313, 327, 401.
- C. floridanus, 327, 402.
- C. gloria-maris, 401.
- C. pealei, 327, 402.
Copepoda, 239, 249.
Corallina, 29, 78, 96.
- C. officinalis, 41, 43, 78, 96.
- C. rubrum, 142, 146, 147.
Coralline Crags, 192.
- Zone, 30, 31.
Corallineæ, 78, 95.
Corallite, 146.
Corallum, 146.
Corals, 112.
Cordate, 302.
Cormophytes, 25.
Cornacuspongiæ, 100.
Coronula diadema, 255.
Corymorpha pendula, 116.
Coryne, 116, 123.
- C. mirabilis, 116, 123.
Cosmocephala, 160, 170.
- C. ochracea, 160, 170.
Costæ, 302.
Cowry-shell, 377.
Crabe enragé, 274.
Crabs, 244, 247, 272.
- Blue, 275.
- Box-, 287.
- Fiddler-, 241, 282.
- Ghost-, 282.
- Green, 274.
- Hermit-, 264.
- Kelp-, 286.
- Lady-, 276.
- Mud-, 281.
- Oyster-, 287.
- Purple shore-, 281.
- Red, 278.
- Rock-, 277, 280.
- Sand-, 11, 241, 276, 282.
- Sheep-, 285.
- Shore-, 281.
- Spider-, 241, 284.
- Stone-, 280.
- Swimming, 241, 274.
- Toad-, 285.
- Walking, 241.
- Yellow shore-, 281.
Crangon, 240, 260.
- C. franciscorum, 240, 261.
- C. vulgaris, 240, 260.
Crawfish, 240, 259, 261.
Creeping Polyzoa, 193.
Crenulated, 302.
Crepidula, 325, 369.
- C. aculeata, 325, 369.
- C. adunca, 370.
- C. fornicata, 325, 369.
- C. navicelloides, 370.
- C. plana, 325, 369.
- C. rugosa, 370.
Cribrella, 204, 207, 211.
- C. sanguinolenta, 204, 211.
Crimson Bluffs, 33.
Crinoidea, 200, 234.
Crinoids, 202, 235.
- Fossil, 235.
Crisia, 188, 194.
- C. eburnea, 188, 194.
Crossaster, 204, 211.
- C. papposus, 204, 211.
Crucibulum, 325, 370.
- C. spinosum, 325, 370.
- C. striatum, 325, 370.
Crustacea, 238, 244, 248, 257, 262.
Cryptochiton, 323.
- C. stelleri, 323.
Cryptogams, 25.
Cryptolithodes, 240, 271.
- C. sitchensis, 240, 271.
Cryptonemiaceæ, 78, 94.
Cryptozonia, 204, 211.
Crystalline stylet, 302, 341.
Ctenidia, 302.
Ctenodiscus, 204, 208.
- C. corniculatus, 204, 208.
Ctenophora, 112, 115, 154, 155.
Ctenostomata, 189, 197.
Cubomedusæ, 133, 137.
Cucumaria crocea, 231.
- C. lævigata, 231.
Cumacea, 242, 288.
Cutleria, 63, 71.
- C. multifida, 63, 71.
Cutleriaceæ, 63, 71.
Cuttlefishes, 44, 315, 467.
Cuvieria squamata, 232.
Cuvierian organs, 231.
Cyanea, 133, 136, 138.
- C. arctica, 44, 133, 138, 144.
- C. fulva, 133, 139.
- C. versicolor, 133, 139.
Cyanophyceæ, 28, 48, 49.
Cyclomyaria, 472.
Cyclops, 239, 249, 250.
Cyclostomata, 188, 193.
Cydippida, 154, 156.
Cymopolia, 51, 57.
- C. barbata, 51, 57.
Cynthia, 473, 476.
- C. carnea, 473, 476.
- C. partita, 473, 476.
- C. pyriformis, 473, 476.
Cypræa, 326, 334, 377.
- C. aurantia, 377.
- C. exanthema, 326, 378.
- C. moneta, 378.
- C. spadacea, 326, 379.
- C. spurca, 326, 378.
Cypræidæ, 326, 377.
Cypridina, 238.
- C. islandica, 441.
Cyprinidæ, 406, 441.
Cypris, 238.
Cyrena, 311.
Cystoclonium, 77, 83.
- C. cirrhosa, 77, 83.
- C. purpurascens, 77, 83.
Cystoseira, 63, 73.
- C. expansa, 63, 73.
Cytherea, 406, 450.
- C. gigantea, 406, 450.
- C. maculata, 406, 450.
D
Dactylopores, 129.
Dactylozoöids, 129.
Daphnia, 238.
Dasya, 77, 79, 89.
- D. elegans, 77, 89.
- D. plumosa, 77, 89.
Dasycladaceæ, 51, 57.
Dasycladus, 51, 57.
- D. occidentalis, 51, 57.
Decapoda, 240, 257, 301, 468.
Decussated, 303.
Delesseria, 77, 79, 86.
- D. alata, 77, 86.
- D. Leprieurii, 77, 86.
- D. sinuosa, 77, 86.
Delesserieæ, 77, 85.
Dendronotidæ, 324.
Dendronotus, 41, 42, 324, 353.
- D. arborescens, 324, 353.
Dentalidæ, 327, 402.
Dentalium, 268, 327, 328, 404.
- D. dentale, 327, 403.
- D. hexagonum, 327, 403.
- D. pretiosum, 327, 403.
Dermal branchiæ, 208.
Desmacidonidæ, 100.
Desmarestia, 15, 62, 66.
- D. aculeata, 43, 62, 66.
- D. ligulata, 62, 67.
- D. viridis, 62, 66.
Desmarestiaceæ, 62, 66.
Desmids, 33.
Desmosticha, 217, 221.
Devil's pocket-books, 12.
Dextral, 303, 345.
Diadema, 217, 222.
- D. setosum, 217, 222.
Diadematidæ, 217, 222.
Diastopora, 188, 194.
- D. patina, 188, 194.
Diastylis, 242, 288.
- D. quadrispinosus, 242, 288.
Diatocardia, 300, 324, 356.
Diatomaceæ, 38.
Diatomaceous ooze, 21.
Diatoms, 21, 32.
- Green, 435.
Dibranchiata, 301, 464, 468.
Dictyosiphon, 62, 67.
- D. fœniculaceus, 62, 67.
Dictyosiphonaceæ, 62, 67.
Dictyota, 63, 70.
- D. dichotoma, 63, 70.
- D. fasciola, 63, 70.
Dictyotaceæ, 63, 70.
Diopatra, 10, 161, 178.
- D. cuprea, 161, 178.
Diploria, 141, 148.
- D. cerebriformis, 141, 148.
Discomedusæ, 133, 137.
Distribution of algæ, 30.
- Of animal life in the sea, 23.
Doliidæ, 326, 379.
Doliolum, 472.
Dolium, 310, 326, 379.
- D. galea, 326, 379.
- D. perdix, 326, 379.
Donacidæ, 406, 445.
Donax, 10, 406, 445.
- D. californicus, 406, 445.
- D. variabilis, 406, 445.
Dorididæ, 324.
Doris, 309, 324, 354.
- D. bilamellata, 324, 354.
Dorocidaris, 217, 222.
- D. Blakei, 217, 222.
- D. papillota, 217, 222.
Dorsal surface, 201, 202.
Dosinia, 406, 450.
- D. discus, 406, 450.
- D. elegans, 406, 450.
Drill, 383.
Dromia, 105.
Dromidæ, 240, 264.
Dulse, 38.
Dumontieæ, 78, 94.
E
Ears, 247, 435.
- Of corn, 12.
Echidnocerus, 240, 270.
- E. cibarius, 240, 270.
- E. foriminatus, 240, 271.
Echinanthidæ, 217, 224.
Echinanthus, 217, 225.
- E. rosaceus, 217, 225.
Echinarachnius, 217, 225.
- E. excentricus, 217, 225.
- E. parma, 44, 217, 225.
Echinaster, 204, 211.
- E. sentus, 204, 211.
Echinasteridæ, 204, 211.
Echinidæ, 217, 223.
Echinodermata, 200, 202, 305.
Echinoidea, 200, 203, 217, 218, 221.
Echinometra, 217, 223.
- E. subangularis, 217, 223.
Echinometridæ, 217, 223.
Echinus, 217, 224.
- E. gracilis, 217, 224.
Ectocarpaceæ, 28, 62, 64.
Ectocarpus, 28, 29, 62, 64.
- E. Hooperi, 29.
- E. littoralis, 62, 64.
- E. siliculosus, 62, 65.
- E. tomentosus, 62, 65.
- E. viridis, 62, 65.
Ectoderm, 101, 118.
Ectoprocta, 188, 193.
Edwardsia, 144.
Eel-grass, 12.
Egg-capsules, 314.
Egg-cases, 11, 12, 367.
Eggs, 248, 314, 343, 414.
Elachista, 62, 67.
Elachistaceæ, 67.
Elytra, 173.
Embryology, 20.
Encœliaceæ, 62, 65.
Encope, 217, 226.
- E. michelini, 217, 226.
Endoderm, 101, 118.
Endopodite, 243, 246.
Ensis, 310, 407, 458.
- E. americanus, 458.
- E. directus, 407, 458.
Entalis, 327.
- E. striolata, 327, 403.
Enteromorpha, 26, 30, 51, 55.
- E. clathrata, 51, 55.
- E. compressa, 51, 55.
- E. intestinalis, 51, 55.
- E. lanceolata, 51, 56.
Entomostraca, 238, 249.
Entoprocta, 189, 198.
Ephyrula, 136.
Epialtus, 241, 286.
- E. productus, 241, 286.
Epidermis, 303, 345, 347.
Epimera, 243.
Epipodite, 243.
Epistoma, 243.
Epizoanthus americanus, 267.
Equilateral, 418.
Equivalve, 418.
Erect Polyzoa, 193.
Errantia, 161, 173, 180.
Escharella, 188, 197.
- E. variabilis, 188, 197.
Escharina, 188.
Escutcheon, 418.
Esperiopsis, 100.
- E. quatsinoensis, 100.
Eucheuma, 77, 84.
- E. isiforme, 77, 84.
Eucope, 125.
- E. diaphana, 116, 125.
Eucratea, 188, 195.
E. chelata, 188, 195.
Eudendrium ramosum, 116, Plate XLI.
Eugorgia aurantica, Plate XLVI.
Eulamellibranchiata, 301, 406, 420, 438.
Eunicea lugubris, Plate XLVII.
Eunicidæ, 161, 178.
Eupagurus kroyeri, 267.
- E. prideaux, 267.
- E. pubescens, 267.
Eupanopeus, 241.
- E. herbstii, 241, 281.
Euphausia, 239, 247.
Euphyllopoda, 238.
Eupleura, 326, 384.
- E. caudata, 326, 384.
Euryalida, 213, 215.
Eurypanopeus, 241.
- E. depressus, 241, 281.
Euspongia, 100, 107.
- E. officinalis, 100, 107.
- E. officinalis, var. adriatica, 100, 108.
- E. officinalis, var. dura, 100, 108.
- E. officinalis, var. mollissima, 100, 108.
- E. officinalis, var. rotunda, 100, 108.
Eusponginæ, 100.
Euthora, 77, 83.
- E. cristata, 77, 83.
Exopodite, 243, 246.
Exoskeleton, 201, 203, 205.
Ex-umbrella, 120.
Eyes, 247, 322, 333, 415, 416.
F
Family, 20.
Fasciolaria, 311, 327, 331, 397.
- F. distans, 327, 397.
- F. gigantea, 327, 397.
- F. tulipa, 327, 397.
Fasciolariidæ, 327.
Feather-stars, 200, 234.
Fenja, 144.
Fiddler-crabs, 12, 241, 282.
Filamentous plants, 26.
Filibranchiata, 301, 405, 420, 423.
Finger-pores, 129.
Fissurella, 324, 357.
- F. alternata, 324, 357.
- F. aspersa, 324.
- F. barbadensis, 324, 357.
Fissurellidæ, 324, 357.
Flagellate Infusoria, 102.
Flatworms, 164.
Florideæ, 28, 31, 76.
Flustra, 188, 196.
- F. foliacea, 192.
- F. membranacea, 188, 196.
Flustrina, 188.
Foot, 303, 317, 320, 321, 328, 415.
- Gasteropod, 334.
Foraminifera, 21, 22.
Fossette, 303, 418.
Fovia, 160, 167.
- F. Warrenii, 160, 167.
Free-swimming colonies, 130.
Frond, 26.
Fucaceæ, 27, 63, 71.
Fucus, 15, 17, 30, 63, 64, 72.
- F. ceranoides, 63, 73.
- F. furcatus, 63, 73.
- F. serratus, 63, 73.
- F. vesiculosus, 38, 63, 72.
Fulgur, 10, 11, 310, 314, 327, 330, 394.
- F. canaliculata, 12, 327, 395.
- F. carica, 12, 327, 395.
- F. perversa, 327, 396.
- F. pyrum, 327, 396.
Functional siphon, 331.
Fuscous, 303.
Fusiform, 303.
G
Gammarus, 9, 43, 242, 290.
- G. annulatus, 290.
- G. locusta, 242, 290.
- G. mucronatus, 290.
Gasteropoda, 300, 320, 324, 328, 335.
Gastric mill, 243, 247.
Gastropores, 129.
Gelasimus minax, 282.
- G. pugilator, 282.
- G. pugnax, 282.
Gelatinous, 27.
Gelidieæ, 76, 80.
Gelidium, 76, 80.
- G. corneum, 76, 80.
- G. Coulteri, Plate XVII.
Generic name, 28.
Genus, 20.
Geographical distribution, 308.
Gephyrea, 171, 185.
Geryonopsidæ, 116, 128.
Ghost-crab, 282.
Giant crab of Japan, 244.
Gigartina, 28, 76, 81.
- G. mamillosa, 76, 81.
- G. microphylla, 76, 81.
- G. radula, 76, 81.
- G. spinosa, 76, 81.
Gigartinaceæ, 28, 76, 80.
Gills, 247, 329, 336, 413.
Girdle, 322.
Glass-rope sponge, 102.
Globigerina, 21.
Globigerina ooze, 21.
Gloiosiphonia, 78, 94.
- G. capillaris, 78, 94.
Gloiosiphonieæ, 78, 94.
Glove sponge, 104.
Glycera, 161, 180.
- G. americana, 161, 180.
- G. dibranchiata, 161, 180.
Glyceridæ, 161, 179.
Glycimeridæ, 407, 459.
Glycimeris, 407, 459.
- G. generosa, 407, 459.
Glyphis, 324, 358.
- G. aspersa, 324, 358.
Gonads, 135, 341.
Gonangium, 118.
Gonophore, 118.
Goose-barnacle, 252.
Gorgonacea, 141, 152.
Gorgonia anceps, Plate XLVI.
- G. flabellum, Plate XLVII.
Gracilaria, 77, 84.
- G. lichenoides, 39.
- G. multipartita, 77, 84.
- G. spinosa, 39.
Grantia, 100, 106.
- G. ciliata, 100, 105, 106.
Grapsidæ, 241, 281.
Grass sponge, 104.
Grateloupia, 78, 94.
- G. Cutleria, 78, 94.
Grateloupieæ, 78, 94.
Green glands, 246.
Griffithsia, 15, 29, 78, 91.
- G. Bornetiana, 78, 91.
- G. corallina, 29.
Grinnellia, 29, 77, 86.
- G. Americana, 29, 77, 86.
Gymnogongrus, 76, 82.
- G. Norvegicus, 76, 82.
Gymnolæmata, 188, 193.
H
Halcyonoida, 141, 150.
Halcyonoids, 142.
Halichondria, 100, 107.
- H. panicea, 100, 107.
Halidrys, 63, 73.
- H. osmunda, 63, 73.
Halimeda, 51, 58.
- H. opuntia, 51, 59.
- H. tridens, 51, 59.
- H. tuna, 51, 58.
Haliotidæ, 324, 358.
Haliotis, 9, 312, 324, 358.
- H. cracherodii, 324, 359.
- H. rufescens, 324, 359.
- H. splendens, 324, 359.
Haliseris, 63, 71.
- H. polypodioides, 63, 71.
Halosaccion, 78, 95.
- H. ramentaceum, 78, 95.
Halymenia, 78, 94.
- H. ligulata, 78, 94.
Haminea solitaria, 324, 351.
Harmothoë, 161, 174.
- H. imbricata, 161, 174.
Heart, 416.
Heart and vascular system, 341.
Heart-urchins, 218, 226.
Heliaster, 204, 205, 212.
- H. multiradiata, 204, 212.
Heliasteridæ, 204, 212.
Helipora, 147.
Helmet-shells, 380.
Helminthocladieæ, 76, 79.
Hemigrapsus, 241, 281.
- H. nudus, 241, 281.
- H. oregonensis, 241, 281.
Hemimyaria, 472.
Herbarium, 17.
Hermit-crabs, 12, 258, 259, 264, 362.
Heterocœla, 100.
Heterograpsus nudus, 281.
- H. oregonensis, 281.
Heterorrhaphidæ, 100.
Hildenbrandtia, 78, 95.
- H. rosea, 40, 78, 95.
Himanthalia, 63, 71.
- H. lorea, 63, 71.
Hippa, 10, 240, 268.
- H. analoga, 240, 269.
- H. talpoida, 10, 11, 240, 268.
Hippasteria, 204, 209.
- H. phrygiana, 204, 209.
Hippidæ, 240, 268.
Hippoconcha, 240, 264.
- H. arcuata, 240, 264.
Hippospongia, 100, 108.
- H. canaliculata, 100, 108.
- H. canaliculata, var. flabellum 100, 109.
- H. canaliculata, var. gossypina, 100, 108.
- H. equina, 100, 108.
- H. equina, var. agaricina, 108.
- H. equina, var. cerebriformis, 100, 108.
- H. equina, var. dura, 108.
- H. equina, var. elastica, 100, 108.
- H. equina, var. meandriformis, 100, 108.
Hircinia, 100, 109.
- H. campana, 100, 109.
Histology, 20.
Holdfasts, 26.
Holocampa, 141, 145.
- H. producta, 141, 145.
Holothuria edulis, 232.
Holothurians, 202, 203.
Holothuroidea, 200, 228, 229.
Homarus, 240, 261.
- H. americanus, 240, 262.
- H. capensis, 261.
- H. vulgaris, 261.
Homorrhaphidæ, 100.
How to arrange a herbarium, 17.
Hyas, 241, 284, 285.
- H. araneus, 241, 285.
- H. coarctatus, 241, 285.
- H. lyratus, 241, 285.
Hybocodon, 124.
- H. prolifer, 116, 124.
Hydractinia, 116, 122.
- H. polyclina, 116, 122, 266.
Hydrallmania falcata, 127.
Hydranth, 118, 119.
Hydrocorallina, 117, 129.
Hydroids, 22, 114, 119.
Hydrorhiza, 118.
Hydrosoma, 118.
Hydrotheca, 118.
Hydrozoa, 112, 114, 116, 119, 120.
Hypnea, 77, 84.
- H. musciformis, 77, 84.
I
Ideal mollusk, 317.
Idotea, 242, 293.
- I. irrorata, 293.
- I. marina, 242, 293.
- I. metallica, 242, 294.
- I. ochotensis, 242, 294.
- I. wosnesenskii, 242, 294.
Idyia, 154, 157.
- I. cyanthina, 154, 158.
- I. roseola, 154, 157.
Inarticulata, 188.
Infusoria, 21, 101.
Interambulacral areas, 201, 202, 218.
Introvert, 186.
Iridæa, 76, 82.
Isopoda, 242, 291.
Isopods, 12.
J
Janthina, 325, 364.
- J. fragilis, 325, 365.
Janthinidæ, 325, 364.
Jellyfishes, 7, 44, 112, 115, 119, 134.
Jonah crab, 277.
K
Kelp, 38.
Kingdom, 19.
Kitchen-middens, 432.
L
Labial palps, 416.
Labiosa canaliculata, 447.
Lacuna, 309, 326, 373.
- L. vincta, 12, 44, 326, 373.
Lady-crab, 276.
Lambrus, 241, 286.
- L. pourtalesii, 241, 286.
Lamellibranchiata, 409.
Lamelliform, 303.
Laminaria, 43, 63, 70.
- L. digitata, 44, 63, 70.
- L. longicruris, 63, 70.
- L. saccharina, 63, 70.
Laminariaceæ, 31, 35, 38, 63, 64, 68.
Laminarian zone, 30,31.
Larva, 201.
Larvacea, 472.
Laurencia, 77, 89.
- L. pinnatifida, 77, 89.
Laver, 38.
Leathesia, 62, 68.
- L. difformis, 41, 68.
- L. tuberiformis, 68.
Leda, 309, 405, 422.
- L. tenuisulcata, 405, 422.
Lepas, 239, 250, 252.
- L. anatifera, 239, 253.
- L. pectinata, 239, 253.
- L. striata, 239, 253.
Leptodora, 238.
Leptogorgia Agassizii, Plate XLVII.
- L. rigida, Plate XLVII.
Leptoliniæ, 116, 121.
Leptomedusæ, 116.
Leptoplana, 160, 166.
- L. folium, 160, 166.
Lessonia, 36, 63.
Leucosolenia, 100, 106.
- L. botryoides, 100, 106.
Liagora, 76.
Libinia, 241, 284.
- L. dubia, 241, 284.
- L. emarginata, 241, 284.
Ligament, 417.
Limnoria, 242, 292.
- L. lignorum, 13, 242, 290, 292.
Limpets, 9.
Limulus, 242, 294.
- L. moluccanus, 295.
- L. polyphemus, 242, 294.
Linerges, 133, 139.
- L. mercurius, 133, 139.
Lines of growth, 344, 347.
Lineus marinus, 167.
- L. sanguineus, 168.
Lingual ribbon, 303, 340.
Lip, inner, 344.
- Outer, 344.
Lithocysts, 135.
Lithodes, 240, 270.
- L. maia, 240, 270.
Lithodidæ, 240, 270.
Littoral, 23.
- Species, 308.
- Zone, 30.
Littorina, 9, 309, 311, 325, 338, 370.
- L. angulifera, 325, 372.
- L. irrorata, 325, 372.
- L. litorea, 8, 41, 42, 325, 371.
- L. palliata, 42, 325, 372.
- L. planaxis, 325, 373.
- L. rudis, 41, 42, 325, 371.
- L. scutulata, 325, 373.
Littorinella minuta, 12.
Littorinidæ, 325, 338, 370.
Livona, 325, 362.
- L. pica, 268, 325, 362.
Lizzia, 120.
Lobata, 154, 156.
Lobsters, 240, 247, 250, 258, 259, 261.
Loligo, 464, 467, 469.
- L. brevis, 464, 469.
- L. Pealei, 464, 469.
Lomentaria, 77, 85.
- L. Baileyana, 77, 85.
Lophophore, 190, 193.
Lophothuria, 228.
- L. fabricii, 228, 232.
Loripes, 406, 443.
- L. edentula, 406, 443.
Lottia, 324, 357.
- L. gigantea, 324, 357.
Lovenia, 217, 227.
- L. cordiformis, 217, 227.
Loxorhynchus, 241, 285.
- L. crispatus, 241, 285.
Lucapina, 324, 358.
- L. crenulata, 324, 358.
Lucernaria, 133, 136.
- L. auricula, 133, 136.
Lucina, 311, 406, 442.
- L. californica, 406, 443.
- L. dentata, 406, 443.
- L. floridana, 406, 442.
- L. nuttallii, 406, 443.
- L. pennsylvanica, 406, 442.
- L. tigrina, 406, 442.
Lucinidæ, 406, 442.
Luidia, 204, 209.
- L. alternata, 204, 209.
- L. clathrata, 204, 209.
- L. senegalensis, 204, 209.
Lumbriconereis, 161, 179.
- L. tenuis, 161, 179.
Lunatia, 12, 309, 314, 325, 367.
- L. heros, 10, 12, 44, 325, 367.
- L. lewisii, 325, 368.
- L. triseriata, 325, 367.
Lunules, 224, 303, 418.
Lyngbya, 48.
- L. æstuarii, 50.
- L. ferruginea, 50.
- L. majuscula, 50.
M
Macoma, 406, 444.
- M. baltica, 406, 445.
- M. nasuta, 406, 444.
- M. proxima, 406, 445.
- M. secta, 406, 444.
- M. tenta, 406, 445.
Macrocystis, 35, 63.
- M. pyrifera, 36, 70.
Macrura, 240, 258, 259, 272.
Mactra, 310, 406, 410, 446.
- M. lateralis, 406, 447.
- M. ovalis, 406, 447.
- M. similis, 406, 447.
- M. solidissima, 406, 446.
Mactridæ, 406, 446.
Madreporic plate, 201, 203, 206, 218.
Maiidæ, 241, 284.
Malacostraca, 239, 257.
Mandibles, 246, 258.
Mantle, 303, 316, 319, 328, 331, 410.
Mantle cavity, 303, 319, 336.
Mantle fusion, 412.
Margarita, 309, 325, 360.
- M. cinerea, 325, 360.
- M. helicina, 12, 44, 325, 360.
- M. undulata, 325, 360.
Margin, 417.
- Anterior, 417.
- Dorsal, 417.
- Posterior, 417.
- Ventral, 417.
Marginella, 311, 327, 399.
- M. apicina, 327, 399.
Marginellidæ, 327, 399.
Marine invertebrates, 97.
Maxillæ, 243, 246, 258.
Maxillipeds, 243, 246, 258.
Meckelia, 160, 169.
- M. ingens, 160, 169.
- M. rosea, 160, 169.
Mediaster, 204, 209.
- M. æqualis, 204, 209.
Megalops, 248, 273.
Meleagrina margaritifera, 313, 430, 431.
Melita nitida, 290.
Mellita, 217, 225.
- M. testudinata, 217, 225.
Melobesia, 78, 96.
Melongena, 311, 327, 396.
- M. corona, 327, 396.
Membranaceous, 27.
Membranipora, 188, 192, 196.
- M. lineata, 188, 196.
- M. pilosa, 43, 188, 196.
- M. tenuis, 188, 197.
Menippe, 241, 280.
- M. mercenaria, 241, 280.
Meristomes, 242, 294.
Mesoderm, 101, 118.
Mesoglœa, 62, 68.
- M. divaricata, 62, 68.
- M. virescens, 62, 68.
Metalia, 217, 227.
- M. pectoralis, 217, 227.
Metameres, 243.
Metapodium, 376.
Metazoa, 101.
Metridium marginatum, 42.
Microciona, 100, 107.
- M. prolifera, 100, 107.
Microcladia, 78, 93.
- M. borealis, 78, 93.
- M. Coulteri, 78, 93.
Millepora, 129.
- M. alcicornis, 117, 129.
Mitra, 313.
Mnemiopsis, 154, 157.
- M. Leidyii, 154, 157.
Modiola, 309, 405, 426.
- M. modiolus, 405, 428.
- M. nigra, 429.
- M. plicatula, 405, 429.
- M. recta, 405, 429.
- M. tulipa, 405, 429.
Mœra levis, 290.
Moina, 238.
Moira, 217, 226.
- M. atropos, 217, 226.
Molgula, 473, 475.
- M. arenata, 473, 476.
- M. manhattensis, 473, 475.
- M. pellucida, 473, 476.
Mollia, 188, 197.
- M. hyalina, 188, 197.
Mollusca, 300, 305, 328.
Monoceras, 312, 326, 387.
- M. engonatum, 326, 388.
- M. lapilloides, 326, 388.
Monomyarian, 303, 430.
Monostroma, 26, 51, 55.
Monotocardia, 300, 325, 364.
Morphology, 20.
Moss-animals, 191.
Mother-of-pearl, 431.
Moulting, 248, 259, 263.
Mounting seaweeds, 16.
Mouth, 329, 333.
Mud-crabs, 12.
Muddy shores, 12.
Multivalve, 307.
Murex, 326, 331, 382.
- M. fulvescens, 383.
- M. pomum, 326, 383.
- M. rufus, 326, 382.
- M. tenuispina, 343, 347.
Muricea specifera, Plate XLVI.
Muricidæ, 326, 381.
Muricinæ, 326, 381, 385.
Muscles, 248.
Musical sands, 2.
Mussel, great horse-, 428.
Mussels, 43, 321, 426.
Mya, 309, 407, 456.
- M. arenaria, 3, 42, 44, 311, 407, 456.
Mycedium fragile, Plate XLV.
Myidæ, 407, 456.
Myrionema, 62, 68.
Mysis, 239, 257.
- M. sternolepsis, 239, 257.
Mytilidæ, 406, 426.
Mytilus, 41, 309, 406, 426.
- M. californicus, 405, 428.
- M. edulis, 42, 43, 287, 405, 427, 428.
- M. hamatus, 405, 428.
N
Naming of plants, 28.
Nanomia, 130.
- N. cara, 117, 130.
Narcomedusæ, 117.
Nassa, 3, 10, 12, 327, 335, 390.
- N. fossata, 327, 391.
- N. mendica, 327, 391.
- N. obsoleta, 10, 12, 327, 390.
- N. perpinguis, 327, 391.
- N. tegula, 327, 391.
- N. trivittata, 10, 11, 327, 390.
- N. vibex, 327, 391.
Nassidæ, 327, 390.
Natica, 311, 325, 334, 367.
- N. canrena, 325, 368.
- N. clausa, 325, 368.
- N. heros, 367.
Naticidæ, 325, 366.
Nauplius, 248, 251.
Nautilus, 328, 467.
Navicula ostrearia, 435.
Nekton, 23.
Nemalion, 76, 79.
- N. multifidum, 76, 79.
Nemalionaceæ, 76, 79.
Nemathelminthes, 159, 161, 170.
Nematoda, 161, 170.
Nematophore, 118.
Nemerteans, 167.
Nemertes, 160, 169.
- N. socialis, 160, 169.
- N. viridis, 160, 169.
Nemertinea, 160, 167.
Neopanopeus, 241.
- N. texana, 241, 281.
Nephridia, 319.
Nephridium, 303.
Nephthydidæ, 161, 177.
Nephthys, 161, 178.
- N. ingens, 161, 178.
- N. picta, 161, 178.
Nereidæ, 161, 176.
Nereis, 161, 176.
- N. limbata, 161, 177.
- N. pelagica, 161, 177.
- N. virens, 161, 177.
Nereocystis, 63, 70.
- N. Lütkeana, 35.
Nerine, 161, 181.
- N. agilis, 161, 181.
- N. coniocephala, 161, 181.
Nerita, 325, 363.
- N. peleronta, 325, 363.
- N. tessellata, 325, 363.
- N. versicolor, 325.
Neritidæ, 325, 363.
Neritina, 311, 325, 363.
- N. reclivata, 325, 364.
- N. viridis, 325, 364.
Nervous system, 247, 320.
Neverita, 309, 325, 368.
- N. duplicata, 11, 325, 367.
- N. recluziana, 325, 368.
Nicothoë, 239, 250.
Nidorella, 204, 210.
- N. armata, 204, 210.
Nitophyllum, 77, 85.
- N. laceratum, 77, 85.
- N. punctatum, 77, 86.
- N. Ruprechteanum, 77, 86.
Noah's-ark shell, 426.
Node, 303.
Nodules, 344.
Non-Calcarea, 100, 104, 106.
Norrisia, 312.
Nostocaceæ, 48.
Nucula, 309, 405, 422.
- N. proxima, 405, 422.
Nuculidæ, 405, 421.
Nudibranch, 328, 349, 353.
Nudibranchiata, 300, 324, 352.
Nullipores, 31, 147.
Nummulites, 22.
O
Obelia, 125.
- O. commissuralis, 116, 125.
Oceania, 125.
- O. languida, 116, 125.
Ocinebra, 326, 384.
- O. circumtexta, 385.
- O. interfossa, 326, 385.
- O. lurida, 326, 384.
- O. poulsoni, 326, 384.
Octopi, 315.
Octopoda, 301, 464, 468.
Octopus, 464, 468.
Oculina, 141, 148.
Ocypoda, 11, 241, 282.
- O. arenaria, 241, 274, 282.
Ocypodidæ, 241, 282.
Odontophore, 303.
Oliva, 10, 311, 313, 327, 334, 400.
- O. literata, 327, 400.
Olivella, 10, 312, 327, 400.
- O. biplicata, 327, 400.
- O. boetica, 327, 401.
- O. mutica, 327, 400.
Olividæ, 327, 400.
Ommastrephes, 464, 468, 469.
- O. illecebrosus, 464, 469.
Opercula, 193.
Operculum, 254, 303, 331, 355.
Ophiocoma, 213, 216.
- O. æthiops, 213, 216.
- O. Alexandri, 213, 216.
- O. riisei, 213, 216.
Ophiopholis, 213, 215.
- O. aculeata, 43, 213, 215.
Ophiothrix, 213, 216.
- O. angulata, 213, 216.
Ophiurida, 213, 215.
Ophiuroidea, 200, 213, 214.
Opisthobranchiata, 300, 324, 349, 350.
Oral, 202.
- Surface, 201.
Orbits, 243.
Orchestia, 11, 43, 242, 289.
- O. agilis, 242, 289.
Organ-pipe coral, 151.
Organs of feeling, 249.
Orifice, 190, 412.
Oscillaria, 48, 49.
Osphradium, 303, 339.
Ossicles, 201, 203, 218.
Ostracoda, 238.
Ostrea, 405, 410, 435.
- O. edulis, 435.
- O. frons, 405, 435.
- O. lurida, 405, 435.
- O. virginica, 310, 405, 435.
Ostreidæ, 405, 432.
Otocysts, 165, 303.
Otter Cliffs, 43.
Ovalipes, 241, 276.
- O. ocellatus, 241, 276.
Ovicell, 190, 193.
Oyster-crab, 287.
Oyster-culture, 432.
Oysters, 321, 432.
- Pearl-, 430, 431, 432.
P
Pacific faunal divisions 311.
Pacygrapsus, 241, 282.
- P. crassipes, 241, 282.
Padina, 63, 71.
- P. pavonia, 63, 71.
Paguridæ, 240, 264.
Pagurus, 240, 267.
- P. bernhardus, 240, 267.
- P. longicarpus, 240, 267.
- P. pollicaris, 240, 267.
Palæmonetes, 240, 260.
- P. vulgaris, 240, 260.
Palæmon vulgaris, 260.
Pallial line, 303, 418.
- Sinus, 303, 419.
Palps, 176, 416.
Palpus, 258.
Panamic province, 312.
Pandora, 407, 463.
- P. trilineata, 407, 463.
Pandoridæ, 407, 463.
Panopeus, 12, 281.
Pantopoda, 242, 296.
Panulirus, 240. 263.
- P. americanus, 263.
- P. argus, 240, 263.
- P. interruptus, 240, 263.
Papillaceous, 303.
Paraphyses, 72.
Parapodia, 171.
Parenchyma, 26.
Parypha, 123.
- P. crocea, 116, 123.
Peachia, 144.
Pearls, 430, 431.
Pecten, 309, 405, 435.
- P. æquisulcatus, 405, 438.
- P. dislocatus, 405, 437.
- P. hastatus, 405, 438.
- P. irradians, 405, 437.
- P. islandicus, 405, 436.
- P. jacobius, 436.
- P. magellanicus, 287, 405, 436.
- P. tenuiscostatus, 436.
Pectinidæ, 405, 435.
Pedal opening, 412.
Pedata, 228, 231.
Pedicellariæ, 201, 205, 219.
Pedicellina, 189, 198.
- P. americana, 189, 198.
Pelagia, 133, 139.
- P. cyanella, 133, 139.
Pelagic, 23.
- Flora, 38.
Pelecypoda, 301, 320, 321, 405, 409, 420.
- Classification of, 419.
Peltogaster, 239, 256.
Pen, 467.
Penæus, 240, 260.
- P. brasiliensis, 240, 260.
- P. setiferus, 240, 260.
Penicillus, 51, 58.
- P. capitatus, 51, 58.
- P. dumentosus, 51, 58.
- P. Phœnix, 51, 58.
Pennaria, 124.
- P. gibbosa, 116, 124.
- P. tiarella, 116, 124.
Pennatula, 141.
- P. aculeata, Plate XLVII.
- P. borealis, Plate XLVII.
Pennatulacea, 141, 153.
Pentaceros, 204, 210.
- P. occidentalis, 204, 210.
- P. reticularis, 204, 210.
Pentacerotidæ, 204, 210.
Pentacrinus, 234, 235.
Pentacta, 228, 232.
- P. frondosa, 43, 228, 232.
Pentagonasteridæ, 204, 209.
Pericardium, 341, 416.
Pericolpa, 133, 136.
- P. quadrigata, 133, 136.
Peridinieæ, 38.
Periostracum, 303, 425.
Perisaltic, 172.
Perisarc, 118, 119.
Peristome, 190, 194, 218, 303.
Peristomium, 176.
Periwinkles, 371.
Perna, 405, 432.
- P. ephippium, 405, 432.
Peromedusæ, 133, 136.
Petricola, 407, 452.
- P. carditoides, 407, 452.
- P. pholadiformis, 407, 452.
Petricolidæ, 407, 452.
Petrocelis, 78, 95.
- P. cruenta, 40, 78, 95.
Petrolisthes, 240, 270.
- P. armatus, 240, 270.
- P. sexspinosus, 240, 270.
Peyssonnelia, 78, 95.
- P. Dubyi, 78, 95.
Phæophyceæ, 28, 61, 62.
Phanerogams, 25.
Phanerozonia, 204, 208.
Phascolosoma, 162, 186.
- P. Gouldii, 162, 186.
Pholadidæ, 407, 460.
Pholas, 407, 460.
- P. californica, 407, 461.
- P. costata, 407, 461.
- P. truncata, 407, 461.
Phoxichilidium, 242, 297.
- P. maxillare, 242, 297.
Phyla, 19.
Phyllitis, 62, 66.
- P. fascia, 62, 66.
Phyllodoce, 161, 175.
- P. gracilis, 161, 175.
Phyllodocidæ, 161, 175.
Phyllolithodes, 240, 271.
- P. papillosus, 240, 271.
Phyllonotus pomum, 382.
Phyllophora, 76, 81.
- P. Brodiæi, 76, 82.
- P. membranifolia, 76, 82.
Phyllopoda, 238.
Phyllospora, 63, 73.
- P. Menziesii, 63, 73.
Phylum, 19.
Phyncopodia helianthoides, 207.
Physalia, 131.
- P. arethusa, 117, 131.
Pikea, 78, 94.
- P. californica, 78, 94.
Pill-bugs, 291.
Pinna, 405, 431.
- P. muricata, 405, 431.
- P. seminuda, 405, 431.
Pinnotheres, 241, 287.
- P. maculatum, 287.
- P. ostreum, 241, 287.
Pinnotheriidæ, 241, 287.
Pitho, 241, 286.
- P. aculeata, 241, 286.
Placunanomia, 405, 425.
- P. macrochisma, 405, 425.
Planaria, 160, 167.
- P. grisea, 160, 167.
Planarians, 166.
Planarian worms, 12.
Plankton, 21, 23.
Planocera, 160, 166.
- P. nebulosa, 160, 166.
Planula, 120, 135.
Platyhelminthes, 159, 160, 164.
Platyonichus ocellatus, 276.
Pleurobrachia, 154, 156.
- P. rhododactyla, 154, 156.
Pleurococcus, 26.
- P. vulgaris, 25.
Plocamium, 77, 85.
- P. coccineum, 77, 85.
Plumularia, 127.
- P. falcata, 116, 127.
Plumularians, 116, 127.
Pluteus, 201, 220.
Polian vessels, 201.
Polina, 160, 170.
- P. glutinosa, 160, 170.
Polychæta, 161, 172.
Polycirrus, 161, 182.
- P. eximius, 161, 182.
Polycladida, 160, 165.
Polyides, 78, 95.
- P. rotundus, 78, 95.
Polymastia, 100, 106.
- P. robusta, 100, 106.
Polynices, 12, 310, 314, 325, 335, 367.
- P. duplicata, 11, 325, 344, 367.
- P. heros, 8, 10, 44, 325, 343, 367.
- P. lewisii, 325, 368.
- P. recluziana, 325, 368.
- P. triseriata, 325, 367.
Polynoë, 161, 174.
- P. squamata, 161, 174.
- P. sublevis, 161, 174.
Polyphemus, 238.
Polypide, 190, 192.
Polyplacophora, 300, 321.
Polyps, 111, 114, 119.
Polysiphonia, 77, 87.
- P. Baileyi, 77, 88.
- P. dendroidea, 77, 87.
- P. fastigiata, 43, 77, 87.
- P. fibrillosa, 77, 88.
- P. Harveyi, 77, 88.
- P. nigrescens, 77, 87.
- P. Olneyi, 77, 88.
- P. parasitica, 77, 87.
- P. urceolata, 77, 88.
- P. urceolata, var. formosa, 77, 88.
- P. variegata, 77, 88.
- P. violacea, 44, 77, 88.
- P. Woodii, 77, 89.
Polyzoa, 8, 188, 191.
Polyzoans, 8, 12, 22.
Pontonema, 161, 170.
- P. marinum, 161, 170.
Porcelanous, 304, 345.
Porcellana, 240, 269.
- P. sayana, 240, 269.
Porcellanasteridæ, 204, 208.
Porcellanidæ, 240, 269.
Porcupine Island, 42.
Porifera, 100, 101.
Porites, 147.
- P. astræaoides, Plate XLV.
- P. furcata, Plate XLV.
Porocidaris, 217, 222.
- P. sharreri, 217, 222.
Porphyra, 43, 78, 96.
- P. laciniata, 78, 96.
- P. vulgaris, 38, 78, 96.
Porpita, 132.
Portunidæ, 241, 274.
Prawns, 258, 259.
Preserving invertebrates, 14.
Prionitis, 78, 94.
- P. Andersonii, 78, 94.
- P. lanceolata, 78, 94.
Proboscis, 333.
Procerodes, 160, 167.
- P. frequens, 160, 167.
Propodium, 335.
Prosobranchiata, 300, 324, 349, 355.
Prostomium, 176, 243.
Protista, 22.
Protobranchiata, 301, 405, 420, 421.
Protococcaceæ, 38.
Protococcus nivalis, 25, 33.
Protophyta, 21.
Protozoa, 21, 101.
Pseudolamellibranchiata, 301, 405, 420, 429.
Psilaster, 204, 209.
- P. floræ, 204, 209.
Psolus ephippiger, 231.
- P. fabricii, 232.
Pterogorgia acerosa, Plate XLVI.
Pteronotus, 326, 384.
- P. festivus, 326, 384.
Ptilota, 78, 92.
- P. densa, 78, 92.
- P. elegans, 78, 92.
- P. hypnoides, 78, 92.
- P. serrata, 78, 92.
Pugettia, 241, 285.
- P. gracilis, 241, 285.
Pulmonata, 300, 331, 338, 349.
Punctaria, 62, 65.
- P. latifolia, 62, 65.
- P. plantaginea, 62, 66.
- P. tenuissima, 62, 66.
Purpura, 8, 9, 309, 312, 326, 386, 387.
- P. crispata, 326, 387.
- P. hæmastoma, 326, 387.
- P. lapillus, 41, 42, 314, 326, 386.
- P. lima, 326, 387.
- P. patula, 326, 386.
- P. saxicola, 326, 387.
Purpurinæ, 326, 385.
Pycnogonida, 242, 296.
Pycnogonidæ, 9.
Pylopagurus, 268.
Pyloric cæca, 208.
Pyrocystis noctiluca, 33.
Pyrosoma, 472.
Pyrosomata, 472.
Pyrula, 10, 326, 379.
- P. papyratia, 326, 379.
R
Radiata, 113.
Radiates, 20.
Radula, 304, 317, 340.
Ræta, 406, 447.
- R. canaliculata, 406, 447.
Ralfsia, 62, 65.
Ralfsiaceæ, 62, 65.
Rataria, 132.
Receptacles, 72.
Red crab, 278.
Red seaweeds, 76, 79.
Red snow, 33.
Reef-builders, 147.
Reef-corals, 142, 146.
Regularia, 217.
Reticulated, 304.
Rhabdocœlida, 160, 167.
Rhabdonia. 77, 83.
- R. Coulteri, 77, 84.
- R. tenera, 77, 83.
Rhithropanopeus, 241.
- R. harrisii, 241, 281.
Rhizocephala, 239, 256.
Rhizophyllideæ, 78, 95.
Rhizostomæ, 133, 139.
Rhodactinia, 141, 145.
- R. davidsii, 141, 145.
Rhodomela, 77, 89.
- R. floccosa, 77, 90.
- R. larix, 77, 90.
- R. Rochei, 77, 89.
- R. subfusca, 77, 89.
Rhodomeleæ, 77, 86.
Rhodophyceæ, 28, 76, 79.
Rhodophyllideæ, 77, 83.
Rhodophyllis, 77, 83.
- R. veprecula, 77, 83.
Rhodospermeæ, 79.
Rhodymenia, 77, 85.
- R. palmata, 38, 42, 43, 77, 85.
Rhodymeniaceæ, 77, 84.
Rhodymenieæ, 77, 85.
Ring-canal, 201, 203.
Rock-crab, 277, 280.
Rockweeds, 8.
Rocky shores, 7.
Rodicks Weir, 44.
Root-mouth jellyfishes, 139.
Rostrum, 243.
Roundworms, 170.
S
Sabella, 162, 184.
- S. microphthalma, 162, 184.
Sabellidæ, 162, 184.
Sacculina, 239, 256.
Sagartia, 141, 145.
- S. leucolena, 141, 145.
Salpa, 472, 474, 475.
Sand-crab, 282.
Sand-dollar, 11, 44, 225.
Sandpiper, 5.
Sandy shores, 10.
Sapphirina, 239, 250.
Sargasso Sea, 33.
Sargassum, 26, 63, 64, 73.
- S. bacciferum, 34, 35, 63, 74.
- S. Montagnei, 63, 74.
- S. vulgare, 63, 74.
Sarsia, 116, 123.
- S. mirabilis, 123.
Saxicava, 41.
Saxidomus, 406, 452.
- S. nuttallii, 406, 452.
Scala, 325, 365.
- S. angulata, 325, 366.
- S. groenlandica, 325, 366.
- S. lineata, 325, 366.
- S. multistriata, 325, 366.
Scalidæ, 325, 365.
Scallops, 12.
Scaphopoda, 320, 321, 327, 402.
Schizaster, 217, 227.
- S. fragilis, 217, 227.
Schizopoda, 239, 257.
Scinaia, 76, 80.
- S. furcellata, 76, 80.
Scrobicularia, 413.
Sculpture, 304.
Scurria, 312.
Scuta, 254.
Scutellidæ, 217, 225.
Scyllarus, 258, 263.
Scyphozoa, 112, 115, 133, 134.
Sea-acorns, 254.
Sea-anemones, 112, 142.
Sea-blubbers, 134.
Sea-colanders, 42, 69.
Sea-cucumbers, 43, 200, 202, 229.
Sea-eggs, 221.
Sea-fans, 114, 115, 142, 147, 152.
Sea-feathers, 152.
Sea-hares, 351.
Sea-lilies, 200, 234.
Sea-mats, 192.
Sea-otters' cabbage, 35.
Sea-peach, 476.
Sea-pens, 142, 153.
Sea-slugs, 349.
Sea-spiders, 9, 296.
Sea-squirts, 474.
Sea-urchins, 43, 114, 200, 203, 218, 220.
Sea-whips, 142, 152.
Sedentaria, 161, 180.
Segment, 243.
Segmented worms, 170.
Semostomæ, 133, 137.
Sense-organs, 135.
Sepia, 464, 467, 468.
Septibranchiata, 420.
Serpula, 162, 185.
- S. dianthus, 162, 185.
Serpulidæ, 162, 184.
Sertularia, 126.
- S. argentea, 43, 116, 127.
- S. cupressina, 116, 127.
- S. pumila, 43, 116, 126.
Sertularians, 8, 116, 120, 121, 126.
Sessile, 121, 126.
Sheep-crab, 285.
Sheepswool sponge, 104, 108.
Shell—
- Butterfly-, 323.
- Coffee-, 379.
- Conch-, 377.
- Cowry-, 377.
- Gasteropod, 342.
- Growth of gasteropod, 346.
- Mounds, 432.
- Noah's-ark, 426.
- Peach-, 454.
- Pelecypod, 416, 417.
- Razor-, 457.
- Setting-sun, 444.
Shipworm, 462.
Shrimps, 240, 245, 258, 259.
Sigaretus, 311, 325, 334, 369.
- S. perspectivus, 325, 369.
Signs on the beach, 1.
Singing Beach, 2.
Sinistral, 304, 345.
Sinuate, 304.
Sipho, 309, 313, 327, 393.
- S. islandicus, 393.
- S. pygmæus, 327, 394.
- S. Stimpsoni, 327, 393.
Siphon, 304, 330, 334, 411.
- Anal, 412.
- Branchial, 412.
- Excurrent, 412.
- Functional, 411.
- Incurrent, 412.
Siphonalia, 327, 394.
- S. kellettii, 327, 394.
Siphoneæ, 51, 56.
Siphonoglyphs, 143.
Siphonophora, 117, 120, 121, 130.
Siphonozoöids, 150.
Siphuncle, 468.
Sipunculoidea, 162, 185.
Sipunculus, 162, 185.
- S. nudus, 162, 185.
Skates, 12, 44.
Solaster, 204, 205, 211.
- S. decemradiata, 204, 211.
- S. endeca, 204, 211.
Solasteridæ, 204, 211.
Solen, 407, 458.
- S. ensis, 3, 458.
- S. rosaceus, 407, 458.
- S. sicarius, 407, 458.
- S. viridis, 407, 458.
Solenidæ, 407, 457.
Solenogastres, 321.
Solenomya, 405, 423.
- S. borealis, 405, 423.
- S. velum 405, 423.
Solenomyidæ, 405, 423.
Somite, 243.
Sow-bugs, 291.
Spatangoidæ, 217, 226.
Spatangoidea, 217, 226.
Species, 20.
Specific name, 28.
Sphacelaria, 62, 65.
- S. cirrhosa, 62, 65.
- S. radicans, 62, 65.
Sphacelariaceæ, 62, 65.
Sphæoplea annulina, 37.
Sphæridia, 219.
Sphærococceæ, 77, 84.
Sphæroma, 242, 293.
- S. destructor, 293.
- S. quadridentatum, 242, 293.
Spicules, 102.
Spider-crabs, 241, 284.
Spines, 201, 205, 221.
Spionidæ, 161, 181.
Spire, 304.
Spirorbis, 8, 12, 162, 185.
- S. borealis, 162, 185.
Spirula, 464, 467, 468.
Spirulina, 48, 49.
Sponges, 100, 101.
Spongia, 104.
- S. graminea, 109.
Spongidæ, 100.
Spongillidæ, 104.
Spongin, 102.
Spring-tides, 13, 15.
Spyridia, 78, 92.
- S. filamentosa, 78, 92.
Squamarieæ, 78, 95.
Squame, 243.
Squids, 464.
Squilla, 241, 288.
- S. empusa, 241, 288.
Starfishes, 43, 114, 200, 203, 204, 205, 434.
Station and habits of the Mollusca, 313.
Stauromedusæ, 133, 136.
Stelosponginæ, 100.
Sternogramme, 76, 82.
- S. interrupta, 76, 82.
Sternorhynchus, 241, 286.
- S. sagittarius, 241, 286.
Stomatopoda, 241, 288.
Stone-canal, 201, 203.
Stone-crab, 280.
Stony corals, 112, 115, 146.
Striæ, 344.
Strobila, 135, 138.
Strombidæ, 326, 375.
Strombus, 10, 311, 326, 376.
- S. alatus, 376.
- S. gigas, 326, 376, 431.
- S. pugilis, 326, 376.
Strongylocentrotus, 217, 223.
- S. drobachiensis, 41, 43, 217, 223.
- S. franciscanus, 217, 223.
- S. purpuratus, 217, 221, 223.
Structure of mollusks, 315.
Stylochopsis, 160, 166.
- S. littoralis, 160, 166.
Suberites, 100, 106.
- S. compacta, 100, 106.
Suberitidæ, 100.
Suborders, 29.
Subumbrella, 120.
Suckers, 201, 203.
Sun-jellies, 134, 138.
Suture, 304, 344.
Swimming-bell, 120.
Swimming crabs, 241.
Syconidæ, 100.
Syllidæ, 161, 173.
Symmetry, 328.
Synapta, 228, 229, 233.
- S. roseola, 228, 233.
- S. rotifera, 228, 233.
- S. tenuis, 228, 233.
- S. viviparia, 231.
T
Table: Classification of algæ—
- Blue-green, 48.
- Brown, 62.
- Grass-green, 51.
- Red, 76.
- Classification of—
- Actinozoa, 141.
- Arthropoda, 238.
- Asteroidea, 204.
- Cephalopoda, 464.
- Chordata, 472.
- Ctenophora, 154.
- Echinoidea, 217.
- Holothuroidea, 228.
- Hydrozoa, 116.
- Mollusca, 300.
- Molluscoida, 188.
- Ophiuroidea, 213.
- Pelecypoda, 409.
- Porifera, 100.
- Scyphozoa, 133.
Tagelus, 310, 407, 459.
- T. gibbus, 407, 459.
Talitrus longicornis, 289.
Talorchestia, 242, 289.
- T. longicornis, 242, 289.
- T. megalophthalma, 290.
Taonia, 63, 71.
- T. atomaria, 63, 71.
Tapes, 406, 451.
- T. laciniata, 406, 451.
- T. staminea, 406, 451.
Tealia crassiformis, 145.
Tectarius, 311, 326, 373.
- T. muricatus, 326.
- T. nodulosus, 326, 373.
Tectibranchiata, 300, 324, 350.
Tedania, 100, 107.
Teeth, 304, 417, 418.
- Cardinal, 418.
- Lateral, 418.
Tellina, 311, 406, 443.
- T. alternata, 406, 444.
- T. bodegensis, 406, 444.
- T. radiata, 406, 443, 444.
- T. tenera, 406, 444.
Tellinidæ, 406, 443.
Telson, 243, 247.
Tentaculocysts, 135.
Terebellidæ, 161, 182.
Teredinidæ, 407, 462.
Teredo, 407, 462.
- T. navalis, 13, 407, 462.
Terga, 254.
Terms used in describing Crustacea, 243.
- Echinoderms, 201.
- Hydroids, 118.
- Mollusks, 302.
- Polyzoa, 190.
Testaceous, 304.
Tetrabranchiata, 301, 464, 467.
Tetrastemma, 160, 169.
- T. arenicola, 160, 169.
Thalassiophyllum, 36, 63, 70.
Thaliacea, 472.
Thallophytes, 25.
Thallus, 26.
Thelepsus, 161, 182.
- T. cincinnatus, 161, 182.
Thorax, 243, 246.
Thracia, 309.
Thyone, 228, 231.
- T. briareus, 228, 231.
Tima, 128.
- T. formosa, 116, 128.
Tivela, 406, 410, 450.
- T. crassatelloides, 406, 450.
Toad-crab, 285.
Toxopneustes, 217, 224.
- T. variegatus, 217, 234.
Trachylinæ, 117, 120, 128.
Trachymedusæ, 117, 128.
Trachynema, 128.
- T. digitale, 117, 128.
Transatlantic province, 309.
Trematoda, 160.
Trichodesmium, 33.
Trichotropis, 309.
Tricladida, 160, 166.
Triclads, 166.
Tridacna gigas, 313, 419.
Triforis, 374.
Tritonidea, 327, 394.
- T. tincta, 327, 394.
Trivia, 326, 378.
- T. californica, 326, 379.
- T. pediculus, 326, 378.
- T. quadripunctata, 326, 379.
- T. solandri, 326, 379.
- T. spadacea, 379.
Trochidae, 325, 359.
Trochiscus, 325, 362.
- T. norrisi, 325, 362.
Trophon, 309, 326, 383.
- T. clathratus, 326, 383.
Tube-feet, 203.
Tubicola, 161, 172.
Tubicolous worms, 180.
Tubipora, 141, 147, 151.
Tubularia, 116.
- T. Couthouyi, 116, 123.
- T. indivisa, 116.
Tubularians, 116, 121, 122.
Tubulipora, 188, 194.
- T. flabellaris, 188, 194.
Tunicata, 472. 474.
Tunicates, 474.
Turbellaria, 160, 165.
Turbinate, 304.
Turbinellidæ, 327, 394.
Turbinidæ, 325, 362.
Turbo, 325, 363.
- T. castaneus, 325, 363.
- T. castaneus, var. crenulatus, 325, 363.
Tyrian purple, 386.
U
Uca, 241, 282.
- U. minax, 241, 282.
- U. pugilator, 241, 282.
- U. pugnax, 241, 282.
Udotea, 51, 58.
- U. conglutinata, 51, 58.
- U. flabellata, 51, 58.
Udoteaceæ, 51, 58.
Ulothrix, 51, 53.
Ulva, 26, 28, 29, 51, 55.
- U. lactuca, 51, 55.
- U. latissima, 51, 55.
- U. Linza, 56.
- U. rigida, 55.
Ulvaceæ, 28, 51, 52, 53, 54.
Umbilicus, 304, 344.
Umbo, 304, 417.
Uncini, 180.
Univalves, 306, 307, 314.
Urochorda, 472, 474.
Urosalpinx, 11, 326, 383, 434.
- U. cinerea, 314, 326, 383.
Uses of algæ, 37.
V
Valoniaceæ, 51, 56.
Valve, 409, 416.
Varices, 304, 344, 347.
Vegetative reproduction, 27.
Vellela, 131.
- V. limbosa, 117, 131.
Velum, 134.
Velutina, 309.
Velvet sponge, 104.
Veneridæ, 406, 447.
Venons sinuses, 247.
Ventral surface, 201.
Ventricose, 304.
Venus, 406, 410, 448.
- V. cancellata, 406, 449.
- V. mercenaria, 406, 448.
- V. mercenaria, var. mortoni, 406, 449.
Venus's flower-basket, 102.
- Girdle, 157.
Vermes, 163.
Vermetidæ, 326, 375.
Vermicularia, 326, 375.
- V. spirata, 326, 375.
Vertebrates, 19.
Vesicularia, 189, 198.
- V. custata, 189, 198.
- V. dichotoma, 189, 198.
Vibracula, 190, 193.
Visceral mass, 415.
Voluta, 313, 327, 398.
- V. junonia, 327, 398, 399.
Volutidæ, 327, 398.
Vulgar names, 29.
W
Walking crabs, 241.
Water-vascular system, 201, 202, 206, 231.
West Indian division, 24.
Wharves and bridges, 13.
Whelks, 44.
Whorl, 304, 343.
Whorls, nepionic, 344.
Worms, 159, 163.
- Bristle-, 171.
- Chætopod, 172.
- Clam-, 176.
- Flat-, 164.
- Nemertean, 167, 169.
- Polychæte, 172.
- Polyclad, 165.
- Round-, 170.
- Segmented, 170.
- Tubicolous, 180.
X
Xiphosura, 242, 294.
Xylotrya, 462.
Y
Yellow sponge, 104.
Yoldia, 309, 405, 422.
- Y. limatula, 405, 422.
- Y. sapotilla, 405, 423.
- Y. thraciæformis, 405, 432.
Z
Zirphæa, 407, 461.
- Z. crispata, 407, 461.
Zoantharia, 141, 142.
Zoarium, 190, 192.
Zoëa, 248, 263, 273.
Zoœcium, 190, 192.
Zonaria, 63, 70.
- Z. lobata, 63, 70.
Zoöids, 118, 119.
Zoöphytes, 113, 119.
Zostera marina, 12.
Zygodactyla, 128.
- Z. groenlandica, 116, 128.

CONTENTS
Introduction
PAGE
I	Signs on the Beach	1
II	Collecting	6
III	Classification	19
IV	Animal Life in its Lowest Forms	21
V	Distribution of Animal Life in the Sea	23
VI	Some Botanical Facts about Algæ	25
VII	Naming of Plants	28
VIII	Distribution of Algæ	30
IX	Some Peculiar and Interesting Varieties of Algæ	32
X	Uses of Algæ	37
XI	Collecting at Bar Harbor	40
PART I
Marine Algæ
I	Blue-Green Seaweeds (Cyanophyceæ)	47
	Grass-Green Seaweeds (Chlorophyceæ)	47
II	Olive-Green and Brown Seaweeds (Phæophyceæ)	61
III	Red Seaweeds (Rhodophyceæ or Florideæ)	75
PART II
Marine Invertebrates
I	Porifera (Sponges)	99
II	Cœlenterata (Polyps)	111
III	Worms (Platyhelminthes, Nemathelminthes, Annulata)	159
IV	Molluscoida	187
V	Echinodermata	199
VI	Arthropoda	237
VII	Mollusca	299
VIII	Chordata	471
	Index	479

PLATE XLVI. GORGONIAS.
Eugorgia aurantica.	Muricea specifera.
Pterogorgia acerosa.	Gorgonia anceps.

PLATE XLVII.
Leptogorgia rigida (a gorgonia).	Eunicea lugubris (a gorgonia).
Gorgonia flabellum (a gorgonia).	Leptogorgia Agassizii (a gorgonia).
	Pennatula borealis and P. aculeata (sea-pens).

Rhodymeniaceæ, suborder Ceramieæ		Callithamnion
		Griffithsia
		Ceramium

PLATE LI.
Flustra foliacea.	1, Flustra membranacea; 2, 3, F. membranacea, magnified.
1, 2, Cellepora pumicosa, natural size; 3, C. pumicosa, magnified; 4, C. ramulosa.	Vesicularia dichotoma.

PLATE LII.
Ctenodiscus crispatus.	Astropecten articularis.
Luidia clathrata.	Hippasteria phrygiana.
Pentaceros reticularis.

PLATE LIII.
Nidorella armata.	Asterina miniata.
Solaster decemradiata.	Crossaster papposus.

PLATE LIV.
Cribrella sanguinolenta.	Heliaster multiradiata.
Asterias Forbesii.	Asterias ochracea.

PLATE LV.
Astrophyton.	Ophiopholis aculeata.
Ophiocoma æthiops.	Ophiocoma Alexandri.
Ophiothrix angulata.	Amphiura squamata.

PLATE LVII.
Porocidaris sharreri.	Dorocidaris Blakei.
Arbacia punctulata.
Diadema setosum.	Strongylocentrotus franciscanus.

PLATE LVIII.
Clypeaster ravenellii.	Mellita testudinata.
Encope michelini.	Test of Metalia pectoralis.
Lovenia cordiformis.

PLATE LXI.
1, Hippa talpoida.	2, Albunæa gibbesii.
3. 1, Porcellana sayana; 2, Petrolisthes armatus; 3, Petrolisthes sexspinosus.
4, Lithodes maia.

PLATE LXII.
Echidnocerus cibarius.	Cryptolithodes sitchensis.
Echidnocerus foriminatus.	Phyllolithodes papillosus.

PLATE LXIII.
Hemigrapsus nudus.	Hyas araneus.
Ocypoda arenaria.	Pugettia gracilis.
Libinia dubia.	Pitho aculeata.

PLATE LXIV.
Calappa flamma.	Calappa flamma, claws open, showing form of cockscomb.
Lambrus pourtalesii.	Limulus polyphemus.

PLATE LXV.
Bulla occidentalis, enlarged.	Bulla nebulosa.
Lottia gigantea, inside view.	Fissurella alternata.

PLATE LXVI.
1, Lucapina crenulata.	3, Chlorostoma brunneum.
2, Haliotis splendens.	4, Neritina reclivata, enlarged.
5, Trochiscus norrisi.

PLATE LXVII.
Livona pica, reduced.	Turbo castaneus, enlarged.
Nerita peleronta.	Chlorostoma funebrale.
Nerita tessellata.

PLATE LXVIII.
Janthina fragilis.	Sigaretus perspectivus, upper side.
Scala angulata, enlarged.	Sigaretus perspectivus, under side.
Natica canrena.	Crepidula aculeata.

PLATE LXIX.
1, Littorina angulifera, twice natural size.	4, Cerithium floridanum.
2, Littorina scutulata, much enlarged.	5, Cerithium muscarum.
3, Littorina planaxis, enlarged.	6, Cerithidea scalariformis, enlarged.
7, Cerithidea sacrata.

PLATE LXX.
1, Strombus pugilis.	3, Trivia pediculus.
2, Cypræa exanthema.	4, Trivia californica.
5, Trivia quadripunctata.

PLATE LXXI.
Dolium galea.	Dolium perdix.
Pyrula papyratia.
Cassis testiculus.	Cassis inflata.

PLATE LXXII.
Murex rufus.	Murex pomum.	Ocinebra poulsoni, enlarged.
Pteronotus festivus.	Cerostoma foliatum.	Cerostoma nuttallii.

THESEA-BEACH AT EBB-TIDE

PREFACE

CONTENTS

INTRODUCTION

INTRODUCTION ISIGNS ON THE BEACH

II COLLECTING

ROCKY SHORES

SANDY SHORES

MUDDY SHORES

WHARVES AND BRIDGES

EQUIPMENT FOR COLLECTING INVERTEBRATES

PRESERVING INVERTEBRATES

COLLECTING AND PRESERVING SEAWEEDS

HOW TO ARRANGE A HERBARIUM

IIICLASSIFICATION

IV ANIMAL LIFE IN ITS LOWEST FORMS

V DISTRIBUTION OF ANIMAL LIFE IN THE SEA

VI SOME BOTANICAL FACTS ABOUT ALGÆ

VIINAMING OF PLANTS

VIII DISTRIBUTION OF ALGÆ

IX SOME PECULIAR AND INTERESTING VARIETIES OF ALGÆ

DIATOMS AND OTHER MINUTE ALGÆ

RED SNOW

THE SARGASSO SEA

THE LAMINARIACEÆ

XUSES OF ALGÆ

XI COLLECTING AT BAR HARBOR

Part IMARINE ALGÆ

IBLUE-GREEN SEAWEEDS(CYANOPHYCEÆ) GRASS-GREEN SEAWEEDS (CHLOROPHYCEÆ)

TABLE SHOWING THE CLASSIFICATION OF THE BLUE-GREEN SEAWEEDS DESCRIBED IN THIS CHAPTER

BLUE-GREEN SEAWEEDS

TABLE SHOWING THE CLASSIFICATION OF THE GRASS-GREEN SEAWEEDS DESCRIBED IN THIS CHAPTER

GRASS-GREEN SEAWEEDS

ORDER CONFERVACEÆ

ORDER ULVACEÆ

GROUP SIPHONEÆ

ORDER VALONIACEÆ

ORDER DASYCLADACEÆ

ORDER UDOTEACEÆ

ORDER CODIACEÆ

ORDER CAULERPACEÆ

IIOLIVE-GREEN AND BROWN SEAWEEDS(PHÆOPHYCEÆ)

TABLE SHOWING THE CLASSIFICATION OF THE OLIVE-GREEN AND BROWN SEAWEEDS DESCRIBED IN THIS CHAPTER

OLIVE-GREEN AND BROWN SEAWEEDS

ORDER ECTOCARPACEÆ

ORDER SPHACELARIACEÆ

ORDER RALFSIACEÆ

ORDER ENCŒLIACEÆ

ORDER DESMARESTIACEÆ (Named for M. Desmarest, a French naturalist)

ORDER DICTYOSIPHONACEÆ

ORDER ELACHISTACEÆ

ORDER CHORDARIACEÆ ("Cord-like")

ORDER LAMINARIACEÆ

ORDER DICTYOTACEÆ

ORDER CUTLERIACEÆ

ORDER FUCACEÆ

III RED SEAWEEDS (RHODOPHYCEÆ OR FLORIDEÆ)

TABLE SHOWING THE CLASSIFICATION OF THE RED SEAWEEDS DESCRIBED IN THIS CHAPTER

RED SEAWEEDS

ORDER NEMALIONACEÆ

Suborder HELMINTHOCLADIEÆ

Suborder CHÆTANGIEÆ

Suborder GELIDIEÆ

ORDER GIGARTINACEÆ

Suborder RHODOPHYLLIDEÆ

ORDER RHODYMENIACEÆ

Suborder SPHÆROCOCCEÆ

Suborder RHODYMENIEÆ

Suborder DELESSERIEÆ

Suborder RHODOMELEÆ

Suborder CERAMIEÆ

ORDER CRYPTONEMIACEÆ

Suborder GLOIOSIPHONIEÆ

Suborder GRATELOUPIEÆ

Suborder DUMONTIEÆ

Suborder RHIZOPHYLLIDEÆ

Suborder SQUAMARIEÆ

Suborder CORALLINEÆ

ORDER BANGIACEÆ

Part II MARINE INVERTEBRATES

THE
SEA-BEACH AT EBB-TIDE

INTRODUCTION

I
SIGNS ON THE BEACH

II
COLLECTING

III
CLASSIFICATION

IV
ANIMAL LIFE IN ITS LOWEST FORMS

V
DISTRIBUTION OF ANIMAL LIFE IN THE SEA

VI
SOME BOTANICAL FACTS ABOUT ALGÆ

VII
NAMING OF PLANTS

VIII
DISTRIBUTION OF ALGÆ

IX
SOME PECULIAR AND INTERESTING VARIETIES OF ALGÆ

X
USES OF ALGÆ

XI
COLLECTING AT BAR HARBOR

Part I
MARINE ALGÆ

I
BLUE-GREEN SEAWEEDS
(CYANOPHYCEÆ)

GRASS-GREEN SEAWEEDS
(CHLOROPHYCEÆ)

II
OLIVE-GREEN AND BROWN SEAWEEDS
(PHÆOPHYCEÆ)

III
RED SEAWEEDS
(RHODOPHYCEÆ OR FLORIDEÆ)

Part II
MARINE INVERTEBRATES

I
PORIFERA
(SPONGES)

II
CŒLENTERATA
(POLYPS)

III
WORMS
(PLATYHELMINTHES
NEMATHELMINTHES
ANNULATA)

IV
MOLLUSCOIDA

V
ECHINODERMATA

PLATE LXXIII.
1, Purpura patula.	4, Monoceras lapilloides.
2, Purpura crispata.	5, Monoceras engonatum.
3, Purpura saxicola, enlarged.	6, Chorus belcheri.

PLATE LXXIV.
1, Columbella mercatoria, enlarged.	6, Nassa perpinguis, enlarged.
2, Columbella (Amphissa) corrugata, enlarged.	7, Nassa tegula, enlarged.
3, Columbella (Astyris) gausapata, much enlarged.	8, Siphonalia kellettii, reduced.
4, Nassa fossata, about natural size.	9, Tritonidea tincta.
5, Nassa mendica, enlarged.

PLATE LXXVII.
1, Marginella apicina, enlarged.	3, Olivella biplicata, enlarged.
2, Oliva literata.	4, Conus floridanus.
5, Cancellaria reticulata.

PLATE LXXVIII.
Placunanomia macrochisma.	Arca ponderosa.
Arca noæ.	Mytilus hamatus.

PLATE LXXX.
1, Lucina tigrina.	3, Lucina pennsylvanica.
2, Lucina floridana.	4, Lucina nuttallii.
5, Loripes edentula.

PLATE LXXXI.
1, Tellina alternata.	3, Donax variabilis.
2, Macoma secta.	4, Donax californicus.
5, Ræta canaliculata.

PLATE LXXXII.
Venus cancellata.	Cytherea (Callista) gigantea.
Cytherea (Callista) maculata.	Dosinia discus.

PLATE LXXXIII.
Tivela crassatelloides, one half natural size.	Tapes laciniata, one half natural size.
Chione succincta.	Chione simillima.

PLATE LXXXIV.
1, Cardium magnum, much reduced.	4, Cardium substriatum, enlarged.
2, Cardium isocardia.	5, Cardium corbis (young specimen).
3, Cardium lævigatum.	6, Glycimeris generosa.

PLATE LXXXV. ASCIDIANS.
1, Ascidia callosa.	5, Cynthia placenta.
2, Botryllus Schlosseri.	6, Glandula fibrosa.
3, Cynthia pyriformis.	7, Cynthia condylomata.
4, The same, enlarged.	8, Boltenia clavata.
	9, Cynthia echinata.