"Talk no more of the violet as the emblem of modesty," exclaims De Quatrefages, "look rather at our annelides, that, possessed of every shining quality, hide themselves from our view, so that but few know of the secret wonders that are hidden under the tufts of algæ, or on the sandy bottom of the sea."

In most of the wandering annelides, each segment is provided with variously formed appendages, more or less developed, serving for respiration and locomotion, or for aggression and defence; while in some of the least perfect of the class, not a trace of an external organ is to be found over the whole body. The great Band-worm (Nemertes gigas) is one of the most remarkable examples of this low type of annelism. It is from thirty to forty feet long, about half an inch broad, flat like a ribbon, of brown or violet colour, and smooth and shining like lackered leather. Among the loose stones, or in the hollows of the rocks, where he principally lives on Anomiæ,—minute shells that attach themselves to submarine bodies,—this giant worm forms a thousand seemingly inextricable knots, which he is continually unravelling and tying. When after having devoured all the food within his reach, or from some other cause, he desires to shift his quarters, he stretches out a long dark-coloured ribbon, surmounted by a head like that of a snake, but without its wide mouth or dangerous fangs. The eye of the observer sees no contraction of the muscles, no apparent cause or instrument of locomotion; but the microscope teaches us that the Nemertes glides along by help of the minute vibratory ciliæ with which his whole body is covered. He hesitates, he tries here and there, until at last, and often at a distance of fifteen or twenty feet, he finds a stone to his taste; whereupon he slowly unrolls his length to convey himself to his new resting place, and while the entangled folds are unravelling themselves at one end, they form a new Gordian knot at the other. All the organs of this worm are uncommonly simplified; the mouth is a scarce visible circular opening, and the intestinal canal ends in a blind sack.

Nature has not in vain provided the more perfect annelides with the bristly feet, which have been denied to the Nemertes and the sand-worm. Almost all of them feed on a living prey,—Planarias and other minute creatures—which they enclasp and transpierce with those formidable weapons. Some, lying in wait, dart upon their victims as they heedlessly swim by, seize them with their jaws, and stifle them in their deadly embrace; others, of a more lively nature, seek them among the thickets of corallines, millepores and algæ, and arrest them quickly ere they can vanish in the sand.

But the annelides also are liable to many persecutions. The fishes are perpetually at war with them; and when an imprudent annelide quits its hidden lurking-place, or is uncovered by the motion of the waves, it may reckon itself fortunate, indeed, if it escapes the greedy teeth of an eel or a flat-fish. It is even affirmed of the latter, as it is of the whelks, that they know perfectly well how to dig the annelides out of the sand. The sea-spiders, lobsters, and other crustacea are the more dangerous, as their hard shells render them perfectly invulnerable by the bristling weapons of the annelides.

While the greater part of these worms lead a vagrant life, others, like secluded hermits, dwell in self-constructed retreats which they never leave. Their cells, which they begin to form very soon after having left the egg, and which they afterwards continue extending and widening according to the exigencies of their growth, generally consist of a hard calcareous mass; but sometimes they are leathery or parchment-like tubes, secreted by the skin of the animal, not however forming, as in the mollusks, an integral part of the body, but remaining quite unconnected with it. Thus these tubicole annelides spend their whole life within doors, only now and then peeping out of their prison with the front part of their head.

As they lead so different a life from their roaming relations, their internal structure is very different, for where is the being whose organisation does not perfectly harmonise with his wants? Thus, we find here no bristling feet or lateral respiratory appendages; but instead of these organs, which in this case would be completely useless, we find the head surmounted by a beautiful crown of feathery tentaculæ, which equally serve for breathing and the seizing of a passing prey. Completely closed at the inferior extremity, the tube shows us at its upper end a round opening, the only window through which our hermit can peep into the world, seize his food, and refresh his blood by exposing his floating branchiæ to the vivifying influence of the water.

Do not, therefore, reproach him with vanity or curiosity, if you see him so often protrude his magnificently decorated head; but rejoice rather that this habit, to which necessity obliges him, gives you a better opportunity for closer observation. Place only a shell or stone covered with serpulas or cymospiras, into a vessel filled with sea-water, and you will soon see how, in every tube, a small round cover is cautiously raised, which hitherto hermetically closed the entrance, and prevented you from prying into the interior. The door is open, and soon the inmate makes his appearance. You now perceive small buds, here dark violet or carmine, there blue or orange, or variously striped. See how they grow, and gradually expand their splendid boughs! They are true flowers that open before your eye, but flowers much more perfect than those which adorn your garden, as they are endowed with voluntary motion and animal life.

At the least shock, at the least vibration of the water, the splendid tufts contract, vanish with the rapidity of lightning, and hide themselves in their stony dwellings, where, under cover of the protecting lid, they bid defiance to their enemies.

Not all the tubicole annelides form grottos or houses of so complete a structure as those I have just described. Many content themselves with agglutinating sand or small shell-fragments into the form of cylindrical tubes. But even in these inferior architectural labours of the Sabellas, Terebellas, Amphitrites, &c., we find an astonishing regularity and art; for these elegant little tubes, which we may often pick up on the strand, where they lie mixed with the shells and algæ cast out by the flood, consist of particles of almost equal size, so artistically glued together, that the delicate walls have everywhere an equal thickness. The form is cylindrical, or funnel-shaped, the tube gradually widening from the lower to the upper end. Some of these tubicoles live like solitary hermits, others love company; for instance, the Sabella alveolaris, which often covers wide surfaces of rock, near low-water mark with its aggregated tubes. When the flood recedes nothing is seen but the closed orifices; but when covered with the rising waters, the sandy surface transforms itself into a beautiful picture. From each aperture stretches forth a neck ornamented with concentric rings of golden hair, and terminating in a head embellished with a tiara of delicately feathered, rainbow-tinted tentacula. The whole looks like a garden-bed enamelled with gay flowers of elegant form and variegated colours.

If size alone were a criterion of classification, the Rotifera would have to be ranked among the microscopic Protozoa, as they are scarcely visible to the naked eye; but a more complicated organisation separates them widely from these lowest members of the animal kingdom, and entitles them to be placed next to the worms.

They are chiefly characterised by a remarkable rotatory or ciliary apparatus, whose vibrating motions, whirling the water about in swift circles or eddies, engulf in a fatal vortex their microscopic food, or enable them to swim from place to place. Such is the crystal transparency of these curious little creatures that their internal structure can be easily recognised. The mouth is placed immediately below the rotatory apparatus, and when once an unfortunate animalcule has been driven into its gaping portals, it is presently crushed between a pair of formidable sharp-toothed jaws, which are perpetually in motion, whether the animal is taking food or not. After having undergone the action of this lively apparatus, the aliment passes into a tubular stomach surrounded by a cushion-like mass of cells commonly coloured with the hue of the food, and, therefore, concluded to be connected with the digestive system.

The rotifera are either naked or covered with a sheath, and many inhabit a tube formed by themselves, attached by its lower end to some water-plant, and open at the summit, from which the animal protrudes when it would exercise its active instincts, and into which it retires for repose from labour or for refuge from alarm. The majority, however, have a furcated foot, which is often capable of contraction by a set of telescopic sheathings or false joints, and by which they are enabled to secure a hold of the minute stems of water-plants. This is their ordinary position when keeping their wheels in action for a supply of food or of water; but they have no difficulty in letting go their hold, and either creeping along by alternate contractions and extensions or swimming away in search of a new attachment. From the neck projects a telescopic spur, supposed to be an organ of respiration, and just below this are seen two minute red specks, supposed to be eyes. The first rotifer was discovered by Leeuwenhoek, in 1702; now more than 180 species are known, and new discoveries are constantly adding to their numbers. They are chiefly found in sweet water, but some are inhabitants of the sea, as, for instance, the Synchæta baltica, remarkable for its luminous powers. It measures about 1/125 of an inch in length, and but 1/350 in width, so that it is invisible to the sharpest unassisted sight: but when viewed through a microscope, it appears as a beautiful and richly organised creature, clear as glass and perfectly colourless, except that its stomach is usually distended with yellow food, and that it carries a large red eye, which glitters like a ruby.

"Its motions too," says Mr. Gosse, "are all vivacious and elegant. It shoots rapidly along or circles about in giddy dance, in company with its fellows, sometimes near the surface, at others just over the bottom of the vase in which it is kept. Occasionally the foot with the tiny toes is drawn up into the body and then suddenly thrown down, and bent up from side to side as a dog wags his tail. Sometimes the rotatory organs are brought forward and then spasmodically spring back to their ordinary position, when the little creature shoots forward with redoubled energy. In all its actions it displays vigour and precision, intelligence and will."

CHAP. XV.

MOLLUSCS.

Simple or compound, free or sessile, peopling the high seas or lining the shores, the marine Molluscs, branching out into more than ten thousand species, extend their reign as far as the waves of ocean roll. Though distinguished from all other sea-animals by the common character of a soft unarticulated body, possessing a complicated digestive apparatus, and covered by a flexible skin or mantle, under or over which a calcareous shell is generally formed by secretion, yet their habits are as various as their forms. Some dart rapidly through the waters, others creep slowly along, or are firmly bound to the rock; in some the senses are as highly developed as in the fishes, in others they are confined to the narrow perceptions of the polyp. Many are individually so small as to escape the naked eye, others of a size so formidable as to entitle them to rank among the giants of the sea; some are perfectly harmless and unarmed, others fully equipped for active warfare. It is evident that creatures so variously gifted, and consequently so widely dissimilar in structure, cannot possibly be grouped together in one description, and that each of the four orders, Cephalopoda, Gasteropoda, Pteropoda, and Acephala (Lamellibranchiates, Brachiopods, Polyzoa, and Tunicata), into which they have been subdivided, must be separately brought before the reader, in order to give him a clear and faithful picture of their organisation and mode of life.

The Cephalopods are the most perfect specimens of the molluscan type, as the decapods are the first among the crustaceans. These remarkable creatures consist of two distinct parts: the trunk or body, which, in form of a sack, open to the front, encloses the branchiæ and digestive organs, and the well-developed head, provided with a pair of sharp-sighted eyes, and crowned with a number of fleshy processes, arms or feet, which encircle and more or less conceal the mouth. It is to this formation that the cephalopod owes its scientific name, for as the feet grow from the circumference of the mouth, it literally creeps upon its head.

All the cephalopods are marine animals, and breathe through branchiæ or gills. These are concealed under the mantle, in a cave or hollow, which alternately expands and contracts, and communicates by two openings with the outer world. The one in form of a slit serves to receive the water; the other, which is tubular, is used for its expulsion.

According to the different number of their gills, the cephalopods are divided into two groups. The first, to which the poulp and common cuttle-fish belong, and which comprises by far the majority of living species, has only two sets of gills; while the second, which, in the present epoch, is only represented by a few species of Nautilus, has four, two on each side, according to the number of their arms or feet—for these remarkable organs serve equally well for prehension or locomotion. The first group is again subdivided into two orders, Octopods and Decapods, the former having only eight sessile feet, while the latter possess an additional pair of elongated tentacles, which serve to seize a prey that may be beyond the reach of the ordinary feet, and also to act as anchors to moor them in safety during the agitations of a stormy sea.

Both the arms and tentacles are furnished with suckers disposed along the whole extent of the inner surface of the former, but generally confined to the widened extremities of the latter, where they are closely aggregated on the inner aspect.

In all the octopods the suckers are soft and unarmed. Every sucker is composed of a circular adhesive disk, which has a thick fleshy circumference and bundles of muscular fibres radiating towards the circular orifice of an inner cavity.

This widens as it descends, and contains a cone of soft substance, rising from the bottom of the cavity, like the piston of a syringe. When the sucker is applied to a surface for the purpose of adhesion, the piston, having previously been raised so as to fill the cavity, is retracted, and a vacuum produced, which may be still further increased by the retraction of the plicated central portion of the disk. So admirably are these air-pumps constructed, and so tenacious is their grasp, that, when they have once seized or fixed upon a prey, it cannot possibly disengage itself from their murderous embrace.

In many of the decapods, who, generally seeking their prey in the deeper waters, have to contend with the agile, slippery, and mucus-clad fishes, more powerful organs of prehension have been superadded to the suckers. Thus, in the Calamary the base of the piston is enclosed by a horny hoop, the margin of which is developed into a series of sharp-pointed curved teeth; and in the still more formidable Onychoteuthis each hoop is produced into the form of a long, curved, and sharp-pointed claw (f), which the predacious mollusc presses firmly into the flesh of its struggling victim, and then withdraws by muscular contraction.

Besides the hooked acetabula, a cluster of small simple unarmed suckers may be observed at the base of the expanded part. These add greatly to the animal's prehensile powers, for when they are applied to one another (e), the tentacles are firmly locked together at that point, and the united strength of both the elongated peduncles can be applied to drag towards the mouth any resisting object which has been grappled by the terminal hooks. There is no mechanical contrivance which surpasses the admirable structure of this natural forceps.

The size of the arms and the arrangement of the suckers differ considerably in the various species. In the octopods or poulps, which generally lead a more sedentary creeping life, and, hidden in the crevices of rocks, await the passing prey, the arms, in accordance with their wants, are with rare exceptions longer, more muscular, and stronger, than in the actively swimming decapods, where the two elongated tentacles or peduncles are the chief organs of prehension. In some species we find the arms distinct—in others they are united by a membrane. Some have a double row of suckers on each arm, others four rows, others again but one. So wonderful are the variations which nature, that consummate artist, plays upon a single theme—so inexhaustible are the modifications she introduces into the formation of numerous species, all constructed upon the same fundamental plan, and all equally perfect in their kind.

Thus well provided with the means for seizing and overcoming the struggles of a living prey, the Cephalopods likewise possess adequate weapons for completing its destruction; for their mouth is most formidably armed with two horny or calcareous jaws, shaped like the mandibles of a parrot, playing vertically on each other, and enclosing a large fleshy tongue bristling with recurved horny spines. Hard, indeed, must be the crab which can resist this terrible beak; and when the cuttle-fish has once fixed on the back of a fish, though much larger and stronger than himself, it is in vain for the tortured victim to fly through the water: he carries his enemy with him till he sinks exhausted under his murderous fangs.

Besides their arms, by help of which the Cephalopods either swim or creep, the forcible expulsion of the water through the respiratory tube or infundibulum serves them as a means of locomotion in a backward direction. By those which have an elongated body and comparatively strong muscles, this movement is performed with such violence that they shoot like arrows through the water, or even like the flying-fish perform a long curve through the air.

Thus Sir James Ross tells us, that once a number of cuttle-fish not only fell upon the deck of his ship, which rose fifteen or sixteen feet above the water, and where more than fifty were gathered, but even bolted right over the entire breadth of the vessel, like a sportsman over a five-barred gate. Finally, the fin-like expansion of their mantle renders the nimble decapods good service in swimming. In the Sepias this finny membrane runs along the sides of the body, while in the Calamary it forms a kind of terminal paddle.

It might be supposed that the dibranchiate cephalopods, by their swiftness, their arms, and their powerful jaws, were sufficiently provided with means of attack or defence; but it must be remembered that their body is soft and naked, and that, though well armed in front, they may readily be attacked in the rear. To afford them the additional protection they required, nature, ever ready to minister to the real wants of her children, has furnished them with an internal bag communicating with the respiratory tube, and secreting a large quantity of an inky fluid, which they can squirt out with force in the face of their foe, and which, mixing readily with the water, envelops them in an opaque cloud, and thus screens them from pursuit. But this inky fluid, thus useful to its owner, is often the cause of his destruction by man, who applies it to his own purpose, for the Italian pigment, called sepia, so invaluable to painters in water-colours, is prepared from the inspissated contents of the ink bag of a cuttle-fish. Such is the durability of this colour that even the inky fluid of fossil species has been found to retain its chromatic property. We are told that grains of wheat buried with Egyptian mummies three thousand years ago have germinated; but it is surely still more astonishing that an animal secretion, the origin of which is lost in the dark abyss of countless ages, should remain so long unaltered.

The cephalopods are scattered in vast numbers over the whole ocean, from the ice-bound shores of Boothia Felix to the open main; they seem, however, to be most abundant in temperate latitudes. Some, like the common poulp, constantly frequent the coasts, creeping among the rocks and stones at the bottom; others, like the Cirroteuthis and Ommastrephes, roam about the high seas at a vast distance from the land.

They are generally nocturnal or vespertine in their habits; they abound towards evening and at night on the surface of the seas, but sink to a greater depth, or retire into the crevices of the rocks, as soon as the sun rises above the horizon. Some are of a recluse disposition, and lead a solitary life in the anfractuosities of the littoral zone; others, of a more social temper, wander in large troops along the shores, or over the vast plains of ocean.

Possessing the organs of sense, and the means of locomotion in a high degree of development, the cephalopods may naturally be expected to be far more active and intelligent than the inferior orders of the molluscs. On moonlight nights, among the islands of the Indian Archipelago, Mr. Adams frequently observed the Sepiæ and Octopi in full predatory activity, and had considerable difficulty and trouble in securing them, so great was their restless vivacity, and so vigorous their endeavours to escape. "They dart from side to side of the pools," says the naturalist in his entertaining and instructive account of his journey to those distant gems of the tropical sea, "or fix themselves so tenaciously to the surface of the stones by means of their suckers that it requires great force and strength to detach them. Even when removed and thrown upon the sand, they progress rapidly, in a sidelong shuffling manner, throwing about their long arms, ejecting their ink-like fluid in sudden violent jets, and staring about with their big shining eyes (which at night appear luminous, like a cat's) in a very grotesque and hideous manner."

At the Cape de Verd islands, Mr. C. Darwin was also much amused by the various arts to escape detection used by a cuttle-fish, which seemed fully aware that he was watching it. Remaining for a time motionless, it would then stealthily advance an inch or two, like a cat after a mouse, and thus proceeded, till, having gained a deeper part, it darted away, leaving a dusky train of ink, to hide the hole into which it had crawled.

All the cephalopods are extremely voracious; they destroy on shallow banks the hopes of the fishermen, devour along the coasts and on the high seas countless myriads of young fish and naked molluscs, and kill, like the tiger, for the mere love of carnage. Thus they would become dangerous to the equilibrium of the seas if nature, to counterbalance their destructive habits, had not provided a great number of enemies for the thinning of their ranks.

They form the almost exclusive food of the sperm-whales, and the albatross and the petrels love to skim them from the surface of the ocean. Tunnies and bonitos devour them in vast numbers, the cod consumes whole shoals of squids, and man, as I have already mentioned, catches many millions to serve him as a bait for this valuable fish.

At Teneriffe, in the Brazils, in Peru and Chili, in India and China, various species of cephalopods are used as food. Along the eastern shores of the Mediterranean, the common sepia constitutes now, as in ancient times, a valuable part of the food of the poor. "One of the most striking spectacles," says Edward Forbes, "is to see at night on the shores of the Ægean the numerous torches glancing along the shores, and reflected by the still and clear sea, borne by poor fishermen, paddling as silently as possible over the rocky shallows in search of the cuttle-fish, which, when seen lying beneath the water in wait for his prey, they dexterously spear, ere the creature has time to dart with the rapidity of an arrow from the weapon about to transfix his soft but firm body."

Animals exposed to the attacks of so many enemies must necessarily multiply in an analogous ratio. Their numerous eggs are generally brought forth in the spring. In the species inhabiting the high seas, they float freely on the surface, carried along by the currents and winds, and form large gelatinous bunches or cylindrical rolls, sometimes as large as a man's leg.

The eggs of the littoral cephalopods appear in the form of dark-coloured, roundish or spindle-shaped bodies, of the size and colour of grapes, and hanging together in clusters. They are soft to the touch, with a tough skin, resembling india-rubber; one end is attenuated into a sort of point or nipple, and the other prolonged into a pedicle, which coils round sea-weed or other floating objects, and serves to fix the berry-like bag in its place. At an early stage these "sea-grapes," as they are called by the fishermen, contain a white yolk enclosed in a clear albumen, and nearer maturity the young cuttle-fish may be found within in various stages of formation, until finally, hatched by the heat of the sun, it emerges from the husk perfectly formed, and launches forth into the water.

Some species of cephalopods are only about the size of a finger, while others attain an astonishing size. Banks and Solander, in Cook's first voyage, found the dead carcass of a gigantic cuttle-fish floating between Cape Horn and the Polynesian islands. It was surrounded by aquatic birds, which were feeding on its remains. From the parts of this specimen, which are still preserved in the Hunterian collection, and which have always strongly excited the attention of naturalists, it must have measured at least six feet from the end of the tail to the end of the tentacles.

Near Van Diemen's Land, Péron saw a sepia about as big as a tun rolling about in the waters. Its enormous arms had the appearance of frightful snakes. Each of these organs was at least seven feet long, and measured seven or eight inches round the base. These well authenticated proportions are truly formidable, and fully justify the dread and abhorrence which the Polynesian divers entertain of those snake-armed monsters of the deep; but not satisfied with reality, some writers have magnified the size of the cephalopods to fabulous dimensions. Thus Pernetti mentions a colossal cuttle-fish, which, climbing up the rigging, overturned a three-masted ship; and Pliny notices a similar giant, with arms thirty feet long and a corresponding girth. But all this is nothing to the Norwegian kraken, a mass of a quarter of a mile in diameter, and a back covered with a thicket of sea-weeds. When it comes to the surface, which seems to be but rarely the case, it raises its arms mast-high into the air, and, having enjoyed for a time the lovely daylight, sinks slowly back again into abysmal darkness. Fishermen are said to have landed on a kraken, and to have kindled a fire upon the supposed island for the purpose of cooking their dinner. But even a kraken, thick-skinned as he may be, does not like his back to be converted into a hearth, and thus it happened that the treacherous ground gave way under the mistaken mariners, and overwhelmed them in the waters. Strange that the oriental tale of Sinbad the sailor should thus be re-echoed in the wild legends of the north.

All the dibranchiate cephalopods are destitute of an outward shell, with the sole exception of the Spirula, a small species chiefly found in the South Sea, and of the far more renowned Argonaut, which poets, ancient and modern, have celebrated as the model from which man took the first idea of navigation. Its two sail-like arms expanding in the air, and the six others rowing in the water, the keel of its elegant shell is pictured as dividing the surface of the tranquil sea. But as soon as the wind rises, or the least danger appears, the cautious argonaut takes in his sails, draws back his oars, creeps into his shell, and sinks instantly into a securer depth. Unfortunately there is not a word of truth in this pleasing tale. Like the common octopus, the argonaut generally creeps about at the bottom of the sea, or when he swims, he places his sails close to his shell, stretches his oars right out before him, and shoots backwards like most of his class by expelling the water from his respiratory tube.

As he sits loosely in his shell, he was supposed by some naturalists to be a parasite enjoying the house of the unknown murdered owner; but this is perfectly erroneous, as the young in the egg already show the rudiments of the future shell, and the full-grown animal repairs by reproduction any injury that may have happened to it.

The tetrabranchiate cephalopods, or Nautili, are very differently constructed from their dibranchiate relations. Here, instead of mighty muscular arms, furnished with suckers or raptorial claws, we find a number of small, sheathed, and retractile tentacles (f), surrounding the mouth in successive series, and amounting to little short of a hundred. The head is further provided with a large muscular disk (g), which, besides acting as a defence to the opening of the shell, serves also in all probability as an organ for creeping along the ground, like the foot in the Gasteropods. The mandibles are strengthened by a dense calcareous substance fit to break up the defensive armour of the crustacean or shell-fish on which the animal feeds. There is no ink-bag, no organ of hearing, and the eyes (h) are pedunculated, and of a more simple structure. The handsome pearl-mother and spirally wound shell is divided by transverse partitions (a), perforated in the centre, into numerous chambers (b). The animal takes up its abode in the foremost and largest (b′), but sends a communicating tube or siphon (c) through all the holes of the partitions to the very extremity of the spirally wound shell. Though the empty conch was frequently found swimming on the waters of the Indian Ocean, or cast ashore on the Moluccas or New Guinea, yet it was only in 1829 that the animal was known with any certainty, one having been caught alive by Mr. George Bennett, near the New Hebrides, which, preserved in spirits, is now in the museum of the College of Surgeons. Since then three different species have been found to abound in the waters of the above-named archipelago, of New Caledonia, and of the Feejee and Solomon Islands, where they principally sojourn among the coral reefs at depths of from three to six fathoms. They usually remain at the bottom of the water, where they creep along rather quickly, supporting themselves upon their tentacula, with their head downwards and the shell raised above. After stormy weather, as it becomes more calm, they may be seen in great numbers floating upon the surface of the sea with the head protruded, and the tentacula resting upon the water, the shell at the same time being undermost; they remain, however, but a short time sailing in this manner, as they can easily return to their situation at the bottom of the sea, by merely drawing in their tentacles and upsetting the shell. They are caught in baskets by the natives, who eat them roasted as a great delicacy.

What renders these animals peculiarly interesting is the circumstance that they are the only living representatives of a class which once filled in countless numbers the bosom of the primeval ocean, and whose fossil remains (Orthoceratites, Ammonites) furnish the naturalist with a series of historical documents, attesting the unmeasured age of our planet. What are the ruins, thirty or forty centuries old, that speak of the vanished glories of extinguished empires to these wonderful medals of creation that lead our thoughts through the dim vista of unnumbered centuries to the fathomless abyss of the past.

In point of development of organisation the Gasteropods or snails rank immediately after the Cephalopods. They also have a head plainly distinguishable from the rest of the body, and to which two brilliant black eyes give an animated expression. But their nervous system is far less developed, and while the lively cephalopod is able to swim about, and rapidly to seize a distant prey, almost all the gasteropods creep slowly along upon a flat disk or foot situated below the digestive organs, a formation to which they owe their name of gasteropods or stomach-footers.

The marine snails are divided into several groups according to the different position and arrangement of their gills. In some species these organs form naked or free-swimming tufts on the back (Nudibranchiata) but generally they are variously disposed either in special cavities or under the folds of the mantle. Thus in the Inferobranchiata they are arranged under its inferior border on both sides of the body, or upon one side only, while in the Tectibranchiata they are placed, as in the Nudibranchiata, upon the dorsal aspect of the body, but are protected by a fold of the skin. In the Cyclobranchiata they form a fringe round the margin of the body, between the edge of the mantle and the foot, and in the Scutibranchiata and Pectinibranchiata they are pectinated, or shaped like the teeth of a comb, and placed in a large hollow chamber, which opens externally at the side of the body or above the head.

Nothing can be more elegant or various than the form and arrangement of the gills in most of the nudibranchiate gasteropods. In the Glauci and Scyllææ, we see at each side of the elongated body long arms branching out into tufty filaments; in the Briarei a hundred furcated stems serve for the aëration of the blood. On the back of the Eolides the gills are arranged in rows; in the Dorides they form a wreath or garland round the posterior intestinal aperture.

The beauty of these animals corresponds with their charming mythological names, for every part of them which is not sparkling like the purest crystal shines with the liveliest colours, red, yellow, or azure. Some inhabit the coasts, where they creep along upon a well-developed foot, others live in the deep waters, where they cling to the stems of floating sea-weed with a narrow and furrowed foot, or swim upon their back, using the borders of the mantle and of the branchiæ as oars. Though chiefly living in the warmer latitudes, they are found in every sea, and many interesting species inhabit the British waters: such as the Sea-lemon (Doris tuberculata), which, when its horns and starry wreath of branchiæ are concealed, bears a curious resemblance in size, form, colour, and warty surface to the half of a citron divided longitudinally; the exquisite Eolis coronata, whose crowded clusters of branchial papillæ are radiant with crimson and cerulean tints; and the crested Antiopa, whose transparent breathing organs are tipped with silvery white.

Though they have no shell to cover them, the Nudibranchiata are not left defenceless to the mercy of their enemies. The transparency of their body is a cause of safety to many of them. Some conceal themselves under stones or among the branches of the madrepores, and some on contracting cast off a part of their mantle, which they leave in possession of their hungry foe, while they themselves make their escape.

Among the British Inferobranchiata we find the rare golden or orange-coloured Pleurobranchus plumula, thus named from its branchiæ projecting like a plume from between the mantle and foot in crawling; and among the Tectibranchiata the common sea-hare (Aplysia punctata), which resembles a great naked snail; its back opening with two wide lobes, which can be expanded or closed over the opening at the animal's will. When open, they expose to view on the right side the finely fringed and lobed branchiæ, seated in a deep hollow beneath a fold of the mantle. The uncomely creature glides along over the stones upon its flat fleshy foot and up the slender stems of sea-weeds by bringing the borders of the same locomotive apparatus to meet around the stem, thus tightly grasping it as if enclosed in a tube. While progressing, the fore part is poked forward as a narrow neck furnished with two pair of tentacles, one pair of which, standing erect and being formed of thin laminæ, bent round so as to bring the edges nearly into contact, look like the ears of the timid quadruped, from which the Aplysia has derived its common name. The colour is a dark-brownish purple studded with rings and spots of white. On being disturbed, the sea-hare pours out from beneath the mantle-lobes a copious fluid of the richest purple hue, which however quickly fades, and is of no value in the arts.

More than forty species of Aplysiæ are known, most of them inhabitants of the warmer seas. The acrid humour exuded by the depilatory aplysia, or Aplysia depilans, of the Mediterranean is still supposed by the Italian fishermen to occasion the loss of the hair, and was used by the ancient Romans in the composition of their venomous potions—though it is by no means poisonous. Such are the prejudices resulting from the propensity of man to associate evil qualities with an unprepossessing appearance.

To the Cyclobranchiate order belong the Limpets and the Chitons. The latter, which are the only multivalve shells among the Gasteropods, are spread in more than two hundred species over every shore from Iceland to the Indies, but they are particularly abundant on the coasts of Peru and Chili. Some of the smaller species inhabit our coasts, where they may be found adhering to stones near low water mark. They are coated with eight transverse shelly plates, folding over each other at their edges like the plates of ancient armour, and inserted into a tough marginal band, so as to form a complete shield to the animal. Thus encased in coat of mail, the chitons have the power of baffling the voracity of their enemies by rolling themselves up into a ball like the wood-louse or the armadillo: they are also able to cling with such tenacity to the rock that it is difficult to detach them without tearing them to pieces. The Limpets, or Patellæ, likewise attach their shield-like shell so firmly to a hard body that it requires the introduction of a knife between the shell and the stone to detach them. It has been calculated that the larger species are thus able to produce a resistance equivalent to a weight of 150 pounds, which, considering the sharp angle of the shell, is more than sufficient to defy the strength of a man to raise them. They often congregate in large numbers in one place, and an old writer compares them to nail-heads struck into the rock. More than a hundred species are known; one of which, the Patella cochlear of the Cape, is almost invariably found squatting upon the shell of another species of limpet. The finest and largest varieties abound on the shores of the Oriental seas and the coasts of the Mediterranean, but several of the smaller species are very numerous in our littoral or sub-littoral zone, where they either feast on the green sea-weeds that we find covering at ebb-tide the stones with a thin emerald layer, or upon the coarser olive-coloured algæ. Thus Patella pellucida and Patella lævis, both remarkable for longitudinal streaks of iridescent colours on an olive-shell, may generally be found feeding either on the broad fronds or on the roots and stems of the Laminariæ, or Oar-weeds. To their labours may indeed be partly attributed the annual destruction of these gigantic algæ, for, eating into the lower part of the stems, and destroying the branches of the roots, they so far weaken the base that it is unable to support the weight of the frond, and thus the plant is detached and driven on shore by the waves.