CRUSTACEA.

CRABS—LOBSTERS.

The Crustaceans were included by LinnÆus among his insects, but their internal structure presents such numerous and important differences that modern naturalists have raised them to the dignity of a separate class. They have indeed, in common with the insects, an articulated body, generally cased with hard materials; they are like them provided with jointed legs, with antennÆ or feelers, and their organs of mastication are similarly formed; but insects breathe atmospheric air through lateral pores or tracheÆ, while the crustaceans, being either aquatic animals or constantly frequenting very damp places, have a branchial or a tegumentary respiration. The perfect insect undergoes no further change; the crustacean, on the contrary, increases in size with every successive year. The higher crustacean possesses a heart, which propels the blood, after it has been aËrated in the gills, to every part of the body; in the insect the circulation of the blood is by no means so highly organised. On the other hand many of the insects are far superior in point of intelligence to even the best endowed crustaceans, for here we find no parental care, no mutual affection, no joint labours for the welfare of a large community, no traces of an amiable disposition, but frequent outbursts of an irascible and sanguinary temper. Though the whole of the Crustacea are formed after one and the same general type, and the same fundamental idea may be traced throughout all their tribes, yet the rings of which their body is composed, and the limbs or appendages attached to these segments, undergo such extensive modifications of structure in the various orders into which the class has been divided that even the eye of science has with difficulty made out the true nature of many of their lowest forms. Who, for instance, judging from outward appearances alone, would suppose that the Barnacles and Acorn-shells which he sees riveted to the rock or to a piece of floating timber were relations of the crab or lobster; but a view of their early forms at once points out their real character, for then they appear as active little animals possessing three pairs of legs and a pair of compound eyes, and having the body covered with an expanded shield like that of many of the lower crustaceans. After going through a series of metamorphoses, these larvÆ, tired of a roaming life, attach themselves by their head, a portion of which becomes excessively elongated into the "peduncle" of the Barnacles, whilst in the Balani or acorn-shells it expands into a broad disk of adhesion. The multivalve shell is gradually formed, the eyes are cast away as being no longer needed, and the now useless feet are replaced by six pairs of extremely useful cirrhi, long, slender, many-jointed, tendril-like appendages fringed with delicate filaments and covered with vibratile cilia. These cirrhi, which resemble a plume of purple feathers, and from whose peculiar character the name of the group, Cirrhipoda, is derived, are constantly in motion as long as they are bathed in water, projecting outwards and expanding into an oval concave net, then retracting inwards, and closing upon whatever may have come within their reach. They are so judiciously placed that any small animal which becomes entangled within them can rarely escape, and is at once conveyed to the mouth. The currents produced in the water by their perpetual activity serve also to aËrate the blood, so that these delicate organs act both as gills and as prehensile arms. In spite of their sessile condition, the Cirrhipeds have not been left without protection against hostile attacks, for at the approach of danger they shrink within their shell, and close its orifice against a host of hungry intruders.

Their various families are widely spread over the seas. It is well known that the barnacles frequently attach themselves in such vast numbers to ships' bottoms as materially to obstruct their way, and the acorn-shells often line the coasts for miles and miles with their large white scurfy patches. The CoronulÆ settle so profusely on the skin of the Greenland whale as often to hide the colour of its skin, while the TubicinellÆ exclusively occur on the huge cetaceans of the South Sea. Some of the larger sea-acorns are highly esteemed as articles of food. The Chinese, after eating the animal of Balanus tintinnabulum with salt and vinegar, use the shell, which is about two or three inches high and an inch in diameter, as a lamp, and the flesh of Balanus psittacus on the southern parts of the South American coast is said to equal in richness and delicacy that of the crab.

While the Cirrhipeds grasp their prey as in a living net, the Siphonostomata lead a parasitic life chiefly upon fishes, sucking their juices with a bloodthirsty proboscis. Some (Argulus, Caligus) wander about freely on the body of their victims as grazing animals on their pasture grounds, or even make excursions in the water, where they will turn over and over several times in succession like mountebanks; others (LerneÆ), after having, like the barnacles, indulged in a vagabond existence in their first youth, remain ever after clinging to the spot on which they originally settled, and where their body undergoes such remarkable transformations that not a vestige of the crustacean structure which characterised their erratic life remains.

As we continue to proceed from the lower to the higher forms, we find, on the next stage of crustacean life, the numerous families of the Entomostraca; some bristly-footed (Lophyropoda), with a small number of legs and with respiratory organs attached to the parts in the neighbourhood of the mouth, others gill-footed (Branchiopoda), with numerous foliaceous legs, serving both for respiration and swimming. Some of these creatures, which are generally of such minute size as to be only just visible to the naked eye, have an unprotected body (Branchipus), but generally they are enclosed within a horny or shelly casing, which sometimes closely resembles a bivalve shell in shape and in the mode of junction of its parts, whilst in other instances it forms a kind of buckler, an opening being left behind, through which the members project.

Though enjoying a royal title, the King-crabs, or Limuli, occupy in reality but a low rank among the crustaceans, and are hardly superior in organisation to the Entomostraca. They are of large size, sometimes attaining the length of two feet, and of a very singular structure, the bases of the legs performing the part of jaws. The best-known species comes from the Moluccas, where they are often seen slowly swimming in the sheltered bays, or still more slowly crawling along upon the sandy shores.

In the Edriophthalmia are included the lower crustaceans that have no carapace, and whose thorax and abdomen are distinctly composed of articulated segments. The numerous legs are variously formed in the different genera for springing, walking, or swimming; and respiration is executed by certain portions of the extremities, modified for this purpose in their structure. To this order belong among others the saltatorial sandhoppers (Talitrus), which so frequently jump up before our feet when walking on the wet sea-sand; the ill-famed ChelurÆ and LinnoriÆ, whose devastations in submerged timber almost rival those of the ship-worm, and the parasitical Cyami, which gnaw deep holes into the skin of the whale. The sandhoppers are extremely frequent on the shores of the arctic seas, where they emulate the tropical ants in their speedy removal of decaying animal substances. Thus Captain HolbÖll relates that, having enclosed a piece of shark's flesh in a basket, and let it down to a depth of seventy-five fathoms, in the Greenland sea, he by this means caught within two hours six quarts of these little creatures, while a vast number still followed the basket as it was hauled up.

As the lower crustaceans offer but few points of interest to the general reader, they required but a few words of notice; but the highest order of the class, the Thoracostraca, thus named from the carapace which covers their thorax, so that only the abdomen presents an annular structure, may justly claim a more ample description. The preceding orders had either sessile eyes or none at all; here the movable eyes are fixed on stalks and of a compound structure like those of the insects; each ocular globe consisting of a number of distinct parallel columns, every one of which is provided with its own crystalline lens, receives its separate impression of light, and is thus in itself a perfect eye. Approaches to this structure are seen in some of the lower crustaceans; but here the "ocelli," as these minute individual eyes have been designated, are very numerous. They are at once recognised, under even a low magnifying power, by the facetted appearance of the surface of the compound eye, the facets being either square (Scyllari, &c.) or more commonly hexagonal (Paguri, SquillÆ, &c). The auditory apparatus is likewise highly developed; the sense of smell is known to be very acute; and the antennÆ are delicate organs of touch.

The Thoracostraca are subdivided into the small group of the Stomatopoda, whose branchiÆ are external and the feet prehensile or formed for swimming, and the far more numerous and important Decapods, which are either long-tailed like the scyllarus or short-tailed like the crab. In these the branchiÆ no longer float in the water, but are enclosed in two chambers, situated one at each side of the under surface of the broad shelly plate which covers the back of the animal. Each of these chambers is provided with two apertures, one in the front near the jaws, the other behind.

The disposition of the anterior or efferent orifice varies but little; but in the long-tailed species the afferent or posterior orifice is a wide slit at the basis of the feet, while in the short-tailed kinds it forms a small transverse aperture generally placed almost immediately in front of the first pair of ambulatory extremities. By means of this formation, the short-tailed decapods or crabs, like those fishes that are provided with a narrow opening to their gill covers, are enabled to exist much longer out of the water than the long-tailed lobsters. Some of them even spend most of their time on land; and, still better to adapt them for a terrestrial life, the internal surfaces of the branchial caverns are lined with a spongy texture, and the gill branches separated from each other by hard partitions, so as to prevent them from collapsing after a long penury of water and thus completely stopping the circulation. While in fishes the water that serves for respiration flows from the front backwards, so as not to impede their motions, we find in the interior of the branchial cavity of the decapods a large valve attached to the second pair of maxillary feet, which, continually falling and rising, occasions a rapid current from behind forwards in the water with which the cavity is filled, a structure perfectly harmonising with their retrograde or sidelong movements.

The digestive apparatus of the decapods is of a very complicated structure. The mouth is here furnished with at least eight pieces or pairs of jaws, which pass the food through an extremely short gullet into a stomach of considerable size. This stomach is rendered curious by having within certain cartilaginous appendages, to which strong grinding-teeth are attached. These are placed at the outlet of the stomach, so that the aliment, after being subjected to the action of the jaws, is again more perfectly comminuted by the stomach-teeth before entering the digestive tube. The different pieces composing the masticatory apparatus of the stomach vary considerably in the different genera, and even in the several species of the same genus; but in every case they are always singularly in harmony with the kind of food taken and the general habits of the animal.

To enable the decapods to seize their victims or to defend themselves against their enemies, their anterior thoracic extremities generally assume the form of "chelÆ," claws, or pincers of considerable strength, armed with teeth or sharp hooks, which give them increased powers of prehension. This form results mainly from the state of extreme development in which the penultimate articulation frequently occurs, and its assumption of the shape of a finger by the prolongation of one of its inferior angles. Against the finger-like process thus produced, which is of great strength, and quite immovable, the last articulation can be brought to bear with immense force, as it is put into motion by a muscular mass of great size, and in relation with the extraordinary development of the penultimate articulation. In most cases only the first pair of legs is converted into these formidable weapons, but in the DromiÆ, which are very common in the warmer seas, we find the two posterior pairs of legs, which are of a much smaller size, and raised above the plane of the others, similarly armed. These posterior claws, however, are not intended for active warfare, but merely for strategical purposes, as they serve to hold fast the pieces of sponges, shells, medusÆ, and other marine productions, under whose cover the wily robber approaches and entraps his prey.

While the lower crustaceans abound in the polar seas, the crabs are completely wanting in those desolate regions; their number increases with the warmer temperature of the waters, and attains its maximum in the tropical zone. Here we find the most remarkable and various forms, here they attain a size unknown in our seas; and here they do not, as with us, inhabit solely the salt waters, but also people the brooks and rivers, or even constantly sojourn on land,—as, for instance, the ThelphusÆ and Gecarcini. There are even some species of land-crabs that suffocate when dipped into water. They breathe indeed through branchiÆ, but the small quantity of oxygen dissolved in water does not suffice for the wants of their active respiration. They generally live in the shades of the damp forests, often at a great distance from the sea, concealing themselves in holes. At breeding time they generally seek the shore for the purpose of washing off their spawn, and depositing it in the sand, and no obstruction will then make them deviate from the straight path. They feed on vegetable substances, and are reckoned very excellent food. When taken, they will seize the person's finger with their claw, and endeavour to escape, leaving the claw behind, which for some time after it has been separated from the body, continues to give the finger a friendly squeeze. In the dusk of the evening they quit their holes, and may then be seen running about with great swiftness.

All sandy and muddy coasts of the tropical seas, affording sufficient protection against a heavy sea, swarm with crabs. In the East and West Indies the Gelasimi bore in every direction circular holes in the moist black soil of the coast. One of the claws of these remarkable creatures is much larger than the other, so as sometimes to surpass in size the whole remainder of the body. They make use of it as a door, to close the entrance of their dwelling, and when running swiftly along, carry it upright over the head, so that it seems to beckon like an outstretched hand. One might fancy the crab moved it as in derision of its pursuers, telling them by pantomimic signs, "Catch me if you can!"

As soon as the ebbing flood lays bare the swampy grounds of the mangrove woods, myriads of animals are seen wallowing in the pestiferous mud. Here a fish jumps about, there a holothuria crawls, and crabs run along by thousands in every direction. The black mud along the coast of Borneo assumes quite a brilliant blue tinge, when, at low water, during the heat of the day, the coerulean Gelasimi come forth to feed.

The Venetian lagoons also harbour a vast number of the common Shore-Crab (Portunus MÆnas), the catching of which affords a profitable employment to the inhabitants of those swampy regions. Whole cargoes are sent to Istria, where they are used as bait for anchovies. The fishermen gather them a short time before they cast their shell, and preserve them in baskets, until the moulting process has been effected, when they are reckoned a delicacy even on the best tables. On attempting to seize this crab, it runs rapidly sideways, and conceals itself in the mud; but when unsuccessful, it raises itself with a menacing mien, beats its claws noisily together, as if in defiance of the enemy, and prepares for a valiant defence, like a true knight.

The most valuable short-tailed crustacean of the North Sea is undoubtedly the Great Crab (Cancer pagurus), which attains a weight of from four to five pounds, and is consumed by thousands in the summer, when it is in season and heaviest. It is caught in wicker-baskets, arranged so as to permit an easy entrance, while egress is not to be thought of.

The legs of the crabs are very differently formed in various species. In those which have been called sea-spiders they are very long, thin, and weak, so that the animal swims badly, and is a slow and uncertain pedestrian. For greater security it therefore generally seeks a greater depth, where, concealed among the sea-weeds, it wages war with annelides, planarias, and small mollusks. Sea-spiders are often found on the oyster-banks, and considered injurious by the fishermen, who unmercifully destroy them whenever they get hold of them.

In other species the legs are short, muscular, and powerful, so as rapidly to carry along the comparatively light body. The tropical land-crabs and the genera Ocypoda and Grapsus, which form the link between the former and the real sea-crabs, are particularly distinguished in this respect.

The Rider or Racer (Ocypoda cursor), who is found on the coasts of Syria and Barbary, and abounds at Cape de Verde, owes his name to his swiftness, which is such that even a man on horseback is said not to be able to overtake him. The West Indian ocypodas dig holes three or four feet deep, immediately above high-water mark, and leave them after dusk. Towards the end of October they retire further inland, and bury themselves for the winter in similar holes, the opening of which they carefully conceal.

In the Portuni, or true Sea-crabs, finally, we find the hind pair of legs flattened like fins, so that they would cut but a sorry figure on the land, but are all the better able to row about in their congenial element.

A strange peculiarity of many crabs is the quantity of parasites they carry along with them on their backs. Many marine productions, both of a vegetable and animal nature, have their birth and grow to beauty on the shell of the sea-spider. Corallines, sponges, zoophytes, algÆ, may thus be found, and balani occasionally cover the entire upper surface of the body of the crab. "All the examples of the Inachus Dorsettensis which I have taken," says the distinguished naturalist, Mr. W. Thompson of Belfast, "were invested with sponge, which generally covers over the body, arms, and legs; algÆ and zoophytes likewise spring from it." In this extraneous matter some of the smaller zoophytes find shelter, and, together with the other objects, render the capture of the Inachus Dorsettensis interesting far beyond its own acquisition. In Mr. Hyndman's collection, there is a sea-spider carrying on its back an oyster much larger than itself, and covered besides with numerous barnacles. Like Atlas, the poor creature groaned under a world.

The extraneous matters which so many crabs carry along with them are, however, far from being always a useless burden; they are often a warlike stratagem, under cover of which the sly crustacean entraps many a choice morsel. Thus Bennett witnessed at Otaheite the proceedings of an interesting Hyas species, which disguised itself by investing its body with a covering of decayed vegetable substances and coral-sand. The better to ensnare its prey, the back was covered with rigid and incurved bristles, calculated to retain the extraneous substances, while the short and well concealed forceps-claws were ready for the attack, and the ophthalmic peduncles, curving upward to raise the eyes above the pile of materials, gave the wily crab the great advantage of seeing without being seen. As soon as an unfortunate mollusk, unsuspicious of evil, approached the lurking ruffian, he darted upon it like an arrow, and, ere it could recover its presence of mind, was busy tearing it to pieces.

If many crabs are burdened with small animals and plants, others live parasitically in the shells of mollusks. Thus the small Pinnotheres veterum claims the hospitality of the Pinna, a large bivalve of the Mediterranean. The ancients supposed that this was a friendly connection, an entente cordiale, formed for mutual defence: that the Pinna, being destitute of eyes, and thus exposed when he opened his shell to the attacks of the cuttle-fish and other enemies, was warned of their approach by his little lodger, upon which he immediately closed his shell and both were safe. Unfortunately, there is not a word of truth in the whole story. The sole reason why the Pinnotheres takes up its abode under a stranger's roof is the softness of its own integuments, which otherwise would leave it utterly defenceless; nor does the Pinna show the least sign of affection for its guest, who, on returning from an excursion, often finds it very difficult to slip again into the shell.

According to Mr. Thompson, the Modiola vulgaris, a species of mussel very common on the Irish coast, almost always harbours several parasitic crabs (Pinnotheres pisum). At Heligoland, Dr. Oetker, to whom we are indebted for the best work on that interesting island, scarce ever found a modiola without several guests of this description, while he never could find any in oysters, mussels, and other nearly related species. What may the reason be of either this predilection or that desertion?

The numerous family of the Paguri, or Hermit crabs, is also condemned by its formation to lead a parasitic and robber-life. The fore part of the body is indeed, as in other crabs, armed with claws and covered with a shield, but ends in a long soft tail provided with one or two small hooks. How then are the poor creatures to help themselves? The hind part is not formed for swimming, and its weight prevents them from running. Thus nothing remains for them but to look about them for some shelter, and this is afforded them by several conchiform shells, buccina, neritÆ, in which they so tenaciously insert their hooked tails, as if both were grown together. So long as they are young and feeble, they content themselves with such shells as they find empty on the strand, but when grown to maturity, they attack living specimens, seize with their sharp claws the snail, ere it can withdraw into its shell, and after devouring its flesh, creep without ceremony into the conquered dwelling, which fits them like a coat when they take a walk, and the mouth of which they close when at rest with their largest forceps, in the same manner as the original possessor used his operculum or lid. How remarkable that an animal should thus find in another creature belonging to a totally different class, the completion, as it were, of its being, and be indebted to it for the protecting cover which its own skin is unable to secrete!

When the dwelling of the pagurus becomes inconveniently narrow, the remedy is easy, for appropriate sea-shells abound wherever hermit crabs exist. They are found on almost every coast, and every new scientific voyage makes us acquainted with new species. According to Quoy and Gaimard, they are particularly numerous at the Ladrones, New Guinea, and Timor. The strand of the small island of Kewa, in Coupang Bay, was entirely covered with them. In the heat of the day they seek the shade of the bushes; but as soon as the cool of evening approaches, they come forth by thousands. Although they make all large snail-houses answer their purposes, they seem in this locality to prefer the large Sea Nerites.

The famous East Indian Cocoa-nut Crab (Birgus latro), a kind of intermediate link between the short and long tailed crabs, bears a great resemblance to the paguri. It is said to climb the palm-trees, for the sake of detaching the heavy nuts; but Mr. Darwin, who attentively observed the animal on the Keeling Islands, tells us that it merely lives upon those that spontaneously fall from the tree. To extract its nourishment from the hard case, it shows an ingenuity which is one of the most wonderful instances of animal instinct. It must first of all be remarked, that its front pair of legs is terminated by very strong and heavy pincers, the last pair by others, narrow and weak. After having selected a nut fit for its dinner, the crab begins its operations by tearing the husk, fibre by fibre, from that end under which the three eye-holes are situated; it then hammers upon one of them with its heavy claws, until an opening is made. Hereupon it turns round, and by the aid of its posterior pincers, extracts the white albuminous substance. It inhabits deep burrows, where it accumulates surprising quantities of picked fibres of cocoa-nut husks, on which it rests as on a bed. Its habits are diurnal; but every night it is said to pay a visit to the sea, no doubt for the purpose of moistening its branchiÆ. It is very good to eat, living as it does on choice vegetable substances; and the great mass of fat, accumulated under the tail of the larger ones, sometimes yields, when melted, as much as a quart of limpid oil. Thus our taking possession of the Keeling Islands, as a coaling station for the steamers from Australia to Ceylon, bodes no good to the Birgus.

The long tail, which the paguri sedulously conceal in shells, serves the shrimps and lobsters as their chief organ of locomotion, for although these creatures have well-formed legs, they make but slow work of it when they attempt to crawl. But nothing can equal the rapidity with which they dart backwards through the water, by suddenly contracting their tail. Thus the Lobster makes leaps of twenty feet at one single bound, and the little shrimp equals it fully in velocity in proportion to its size, and belongs unquestionably to the most active of the denizens of the ocean. It swarms in incalculable numbers on the sandy shores of the North Sea, where it is caught in nets attached to a long cross pole, which the fishermen, walking knee-deep in the water, push along before them. Boiled shrimps are a well known delicacy; and the Squilla Mantis of the Mediterranean, which resembles our common shrimp in outer form, but essentially differs from it in the formation of its branchiÆ, which float freely in the water, attached to the abdominal legs, holds an equal rank in the estimation of the South Europeans.

But of all crustaceans, none approaches the Lobster in delicacy of taste. This creature, the epicure's delight, loves to dwell in the deep clear waters along bold rocky shores, where it is taken in wicker baskets, or with small nets attached to iron hoops. About two millions of lobsters are annually imported from Norway, although they are also found in great abundance along the Scottish and Irish coasts. Thus, considering their high price, they form a considerable article of trade; and yet they are far from equalling in importance the minute Herring-crab (Cancer halecum), which, by forming the chief nourishment of that invaluable fish, renders in an indirect way incalculable services to man.

The lobster breeds in the summer months, depositing many thousands of eggs in the sand, and leaving them there to be hatched by the sun. But few, as may easily be imagined, live to attain a size befitting them to appear in red livery on our tables. Like all crustaceans, the lobster casts its shell annually, and with such perfection, that the discarded garment, with all its appendages, perfectly resembles the living animal. The process is curious enough to deserve a few lines of description.

When towards autumn, the time of casting the shell approaches, the lobster retires to a silent nook, like a pious hermit to his cell, and fasts several days. The shell thus detaches itself gradually from the emaciated body, and a new and tender cuticle forms underneath. The old dress seems now, however, to plague the lobster very much, to judge by the efforts he makes to sever all remaining connection with it. Soon the harness splits right through the back, like the cleft bark of a tree, or a ripe seed-husk, and opens a wide gate to liberty. After much tugging and wriggling, the legs, tail, and claws gradually follow the body. The claws give the lobster most trouble; but he is well aware that perseverance generally wins the day, and never ceases till the elastic mass, which can be drawn out like india-rubber, and instantly resumes its ordinary shape, has been forced through the narrow passage. It can easily be supposed that, after such a violent struggle for freedom, the lobster is not a little exhausted. Feeling his weakness, and the very insufficient protection afforded him by his soft covering, he bashfully retires from all society until his hardened case allows him to mix again with his friends on terms of equality, for he well knows how inclined they are to bite and devour a softer brother.

The facility with which the crustacea cast off their legs, and even their heavy claws, when they have been wounded in one of these organs or alarmed at thunder, is most remarkable. Without the least appearance of pain, they then continue to run along upon their remaining legs. After some time a new limb grows out of the old stump, but never attains the size of the original limb.

At the beginning of the chapter I have already briefly described the wonderful transformations of the barnacles, acorn-shells, and lerneÆ, but the changes which the young crabs, lobsters, prawns, and shrimps, have to undergo ere they assume their perfect form are no less astonishing. Thus in the earliest state of the small edible crab (Carcinus moenas) we find a creature with a preposterously large helmet-shaped head, ending behind in a long spine, and furnished in front with two monstrous sessile eyes like the windows of a lantern. By means of a long articulated tail the restless Chimera continually turns head over heels. Claws are wanting, and while the old crab is of course a perfect decapod, the young has only four bifid legs, armed at the extremity with four long bristles, that are continually pushing food towards the ciliated mouth. Who could imagine that a creature like this should ever change into a crab, to which it has not the least resemblance? But time does wonders. After the first change of skin the body assumes something like its permanent shape, the eyes become stalked, the claws are developed, and the legs resemble those of the crab, but the tail is still long, and the swimming habit has not yet been laid aside. At the next stage, while the little creature is still about the eighth of an inch in diameter, the crab form is at length completed, the abdomen folding in under the carapace. No wonder that these larvÆ were long supposed to be distinct types, and described under the names of ZoËa and Megalops, until Mr. T. J. Thompson first discovered their real nature.

The life history of the Palinuri or spiny lobsters is equally curious. They frequently weigh ten or twelve pounds each, and are distinguished by the very large size of their lateral antennÆ and by their feet being unarmed with pincers. Surely nothing can be more dissimilar than the glass crabs or Phyllosomas, thin as a leaf of paper, and so transparent that their blue eyes are their only visible parts while swimming in the water; and yet these flimsy creatures are nothing but the young of the large and bulky Palinuri.

Though several of the lower crustaceans ascend into the regions of eternal snow, while others hide themselves in the perpetual night of subterranean grottoes; though many delight in the sweet waters of the river or the lake, or rapidly multiply in stagnant pools, yet the chief seat of their class, which altogether comprises about 1,600 known species, is in the ocean and its littoral zone, where their numbers, their voracity, and their powerful claws, render them the most formidable enemies of all the lower aquatic animals that are not swift or cunning enough to escape them. Even the fishes and cetaceans are, as we have seen, exposed to their attacks; and as the whale, the carp, the sturgeon, the shark, the perch, have each of them their peculiar crustacean parasites, it can easily be imagined how large the number of still unknown species must be which feast on that vast host of fishes that has never yet been accurately examined. On the other hand, the crustaceans constitute a great part of the food, as well of the sea-stars, sea-urchins, annelides, and many of the molluscs, as also of the fishes and sea-birds; and as they are found of all sizes, from microscopical minuteness to the gigantic proportions of the Inachus KÆmpferi of Japan, the fore-arm of which measures four feet in length, and the others in proportion, so that it covers about 25 feet square of ground, they are able to satisfy the wants or the voracity of a vast number of enemies, from the rotifer or the polyp that feed on tiny entomostraca or the larvÆ of the barnacle, to man, who selects a great variety of the fat and luscious decapods for his share of the feast.

A great fecundity enables the crustaceans to bear up against all these persecutions. 12,000 eggs have been found on the lobster; 6,807 on the shrimp; 21,699 on the great crab (Platycarcinus pagurus). The lower orders are still more prolific, for such is the rapidity with which many of them come to maturity and begin to propagate that it has been calculated that a single female Cyclops may be the progenitor in one year of 4,442,189,120 young! Endowed with such powers, the crustaceans are not likely to be extirpated, nor to disappoint the hopes of their gastronomical admirers for many an age to come.

When we hear of fishes wandering about on the dry land, we cannot wonder that some insects and arachnidans should depart so strangely from the usual habits of their class as to select the sea for their habitation.

"There is a minute marine spider," says Mr. Gosse, "very common on most parts of the coast, crawling sluggishly upon the smaller sea-weeds, which seems, from its lack of centralisation, to realise our infant ideas of Mr. Nobody; but zoologists have designated him as Nymphon gracile. Widely different from the spiders of terra firma, in which an abdomen some ten times as bulky as all the rest of the animal put together is the most characteristic feature, the belly of our marine friend is reduced to an atom not so big as a single joint of one of his eight legs; though his thorax is more considerable, this is little more than the extended line formed by the successive points of union of the said legs. These latter, on the other hand, are long, stout, well-armed, and many-jointed; but, apparently from the lack of the centralising principle, they are moved heavily, sprawled hither and thither, and dragged about like the limbs of an unfortunate who is afflicted with the gout." This strange little creature has four eyes gleaming like diamonds, respires by the skin, and its stomach is prolonged into each of its eight legs, which are thus made the seats of digestion. Mr. Nobody and his marine relations, some of which also attach themselves to fishes, form the small group of the Pycnogonida (p?????, frequent; ???? knee) thus named from their many-jointed legs.

It is a well-known fact that the winds will sometimes waft butterflies to an immense distance from the shore. Thus Acherontia atropos has been found on the Atlantic a thousand miles from the nearest land; and while Mr. Darwin was in the bay of San Blas, in Patagonia, he saw thousands of butterflies hovering over the sea as far as the eye could reach. These insects, of course, are nothing but stray wanderers on an alien and hostile element; but Leptopus longipes, a species of bug, makes the salt water its home; the Halobates, another hemipterous insect, faces the tranquil mirror of the tropical seas as leisurely as our water-bugs sport on the glassy surface of our ponds, and the Gyrinus marinus, a beetle belonging to the family of the whirligigs, ambitiously seeks a wide expanse, and may be seen curvetting about on the surface of the sea, and darting down every now and then to seize its prey.