As soon as born, the young Crustaceans withdraw from the mother and ascend to the surface of the water, in order to gain the open sea. They swim in a circle; but this pelagic life is not of long duration; they quit it after their fourth moult, which takes place between the thirtieth and fortieth day, at which time they lose the transitory organs of natation which they have hitherto possessed. After this they are no longer able to maintain themselves on the surface, but drop to the bottom. Henceforth they are condemned to remain there, and such walking as they can exercise becomes their habitual mode of progression. As they increase in size they gradually approach the shore, which they had for the moment abandoned, and return to the places inhabited by the parent Crustaceans.

The form of the larvæ differs so much from that of the adult, that it would be difficult, except on the clearest evidence, to determine the species from which they proceed. Former naturalists considered the embryo cray-fish (Palinurus) to belong to a distinct genera, which they designated Phyllosoma. It is now known, however, that these are the young of the higher forms of Crustaceans undergoing metamorphosis. In the various forms of Macroura the metamorphosis is less decided than in the Brachyura. In the fresh-water cray-fish no change whatever takes place. Dissatisfied with the uncertainty of former experiments, Mr. Couch undertook a series of observations, which are recorded in the proceedings of the Cornwall Polytechnic Society, in which he established the fact that metamorphosis takes place in the following genera: Cancer, Xanthò, Plumnus, Carcinus, Portunus, Maja, Galathea, Hornarus, and Palinurus. "Metamorphosis has been demonstrated," says Dr. Bell, "in no less than seventeen genera of the Brachyurous order of Decapoda, in which it is most decided and obvious; in Leptopodia, Majacea, Cancer, Portunidæ, Pinnoteres, and Grapsus. In the Anomourous order it is seen in the Pagurus, Porcellana, and Galathea; and in the Macrouran order in Homarus, Palinurus, Palæmon, and Crangon."

The swimming of these creatures is produced by flexions and expansions of the tail, and by repeated beating motions of the claws, the tail acting as a sort of vibratile oar, aided by which they maintain themselves in the water and facilitate their progress. As the shell becomes more solid they get less active, and finally return to the bottom to cast their shell and assume a new form.

According to the observations of M. Coste, the young lobster casts its shell from eight to ten times in the first year, from five to seven in the second, three to four times the third, and two or three times the fourth year. In the fifth year they attain the adult state. Whence it follows, that the small lobsters served at our tables have changed their calcareous vestment something like twenty-one times, and are now clothed in their twenty-second habit.

The crabs are numerous in species and various in size. The long-clawed crab (Corystes Cassivelaunus) of Pennant and Leach (Fig. 335) is remarkable for its long antennæ, which considerably exceed the body. The jaw-feet have their third joint longer than the second, terminating in an obtuse point, with a notch on its interior edge; eyes wide apart, borne upon large peduncles, which are nearly cylindrical and short; anterior feet large, equal, twice the length of the body, and nearly cylindrical in the males; in the females (Fig. 336) about the length of the body, and compressed, especially towards the hand-claw. The other feet terminate in an elongated nail or claw, which is straight-pointed and channeled longitudinally: carapace oblong-oval, terminating in a rostrum anteriorly truncated and bordered posteriorly; the regions but slightly indicated, with the exception of the cordian region, the branchial or lateral regions being very much elongated.

Latreille gives the name of Corystes, which signifies a warrior armed, to this genus of Crustaceans, from κόρυς, a helmet, but it is perfectly inoffensive. Pennant had already conferred the name of Cassivelaunus, the chief of the Ancient Britons, for the singular reason, according to Gosse, that the carapace, which is marked by wrinkles, bears, in old males especially, the strongest and most ludicrous resemblance to the face of an ancient man. Pennant's well-known sympathy with his British ancestry certainly never led him to caricature the grand old British warrior, as Mr. Gosse surmises. On the contrary, he saw in the Crustacean a creature armed at all points, and he named it after the hero of his imagination.

In this species the surface of the carapace is somewhat granulous, with two denticles between the eyes, and three sharp points directed forward on each side. The male has only five abdominal pieces, but the vestiges of the separation of the two others may be clearly remarked upon the outer mediate or third piece, which is the largest of all. The length of the antennæ is remarked on by Mr. Couch, in his Cornish Fauna. "These organs," he says, "are of some use beyond their common office of feelers; perhaps, as in some other Crustaceans, they assist in the process of excavation; and, when soiled by labour, I have seen the crab effect their cleaning by alternately bending the joints of their stalks, which stand conveniently angular for the purpose. Each of the long antennæ is thus drawn along the brush that fringes the internal face of the other, until both are cleared of every particle that adhered to them." On the other hand, Mr. Gosse suggests that the office of the antennæ is to keep a passage open for ejecting the deteriorated water after it has bathed and aerated the gills. "I have observed," he says, "that, when kept in an aquarium, these crabs are fond of sitting bolt upright, the antennæ placed close together, and pointing straight upwards from the head. This is doubtless the attitude in which the animal sits in its burrow, for the tips of the antennæ may often be seen just projecting from the sand. When the chosen seat has happened to be so close to the glass side of the tank as to bring the antennæ within the range of a pocket lens, I have minutely investigated these organs without disturbing the old warrior in his meditation. I saw on each occasion that a strong current of water was continuously pouring up from the points of the antennæ. Tracing this to its origin, it became evident that it was produced by the rapid vibration of the foot-jaws drawing in the surrounding water, and pouring it off upwards between the united antennæ, as through a tube. Then, on examining these organs, I perceived that the form and arrangement of their bristles did indeed constitute each antennæ a semi-tube, so that when the pair were brought face to face the tube was complete."

Among the numerous genera of Brachyurous Crustaceans, Grapsus is distinguished by its less regularly quadrilateral form; the body nearly always compressed, and the sternal plastron but little or not at all curved backwards; the front strongly recurved, or, rather, bent downwards; the orbits oval-shaped and of moderate size; the lateral edges of the carapace slightly curving and trenchant; the ocular pedicles large, but short: their insertion beneath the front and the cornea occupies one-half of their length.

The Hermit or Soldier Crab (Pagurus Bernhardus, Fabricius, Fig. 337) is, perhaps, the oddest and most curious of Crustaceans. It differs from most other Crustaceans in this: in place of having the body protected by a calcareous armour, more or less thick and solid, it has only a cuirass and head-piece to protect the head and breast; all the rest of the body is invested in a soft yielding skin; and this, the vulnerable part of the hermit crab, is the delicate morsel devoured by the gourmet. Nor is our somewhat evil-disposed Crustacean ignorant of the perfectly weak and defenceless state of its posterior quarters. Prudence or instinct makes it seek the shelter of some empty shell, of a shape and size corresponding to its own. When it fails to find one empty, it does not hesitate to attack some living testacean, which it kills without pity or remorse, and takes possession of its habitation without other form of process. Once master of the shell (Fig. 337), it introduces itself, stern foremost, and installs itself as in an entrenchment, where it is established so firmly that it moves about with it more or less briskly, according to its comparative size.

The Pagurians belong to the Anomourous family of Crustaceans, of which there are several genera, and a considerable number of species, the animal economy of which has been ably commented upon by Mr. Broderip. "Their backs," he says, "are towards the arch of the turbinated shell occupied by them, and their well-armed nippers and first two pairs of succeeding feet generally project beyond the mouth of it. The short feet rest upon the polished surface of the columella, and the outer surface of their termination, especially that of the first pair, is in some species most admirably rough-shod, to give 'the soldier' a firm footing when he makes his sortie, or to add to the resistance of the crustaceous holders at the end of his abdomen, or tail, when he is attacked, and wishes to withdraw into his castle. On passing the finger downwards over the terminations of these feet, they feel smooth; but if the finger be passed upwards, the roughness is instantly perceived. The same sort of structure (it is as rough as a file) is to be seen in the smaller caudal holders." In another species of Pagurus, from the Mauritius, which was nearly a foot in length, he found a great number of transverse rows, armed with acetabula, or suckers; these were visible without the aid of a glass, which must very much assist the hold of the Pagurus.

During the feeding and breeding-time, the hermit throws out his head and feet, and especially his great claws, and feels his way with his two antennæ, which are long and slender. When he walks he hooks on with his pincers to the nearest body, and draws his shell after him, as the snail does his. But the undefended parts of the body always remain under cover. At low water the hermits spread themselves over the rocky shore, and the spectator thinks he sees a great number of shells which move in all directions, with allurements different from that which belongs to their essentially slow and measured race. If they are touched they stop suddenly, and it is soon discovered that their shell is the dwelling of a crustacean, not a mollusc. The animal lives alone in its little citadel, like the hermit in his cell or the sentinel in his box. Hence the name of hermit and soldier.

When our crustacean outgrows its borrowed habitation, it sets out in search of another shell, a little larger, and better suited for its increased size.

The hermit often avails itself, as we have said, of empty shells abandoned by their owners; when the tide retires these seldom fail them, and the hermit may be seen examining, turning, and returning, and even trying its new domicile. It glides slowly along on its abdomen, which is large and somewhat distorted, sometimes in one shell, sometimes in another, looking defiantly all round it, and returning very quickly to its ancient lodging if the new one does not turn out to be perfectly comfortable, often trying a great number, as a man might try many new clothes before suiting himself. In its successive removals the little sybarite chooses a hermitage more and more spacious, according to its taste or caprice in colour or architecture. The cunning little creature chooses its mansion, now grey or yellow, now red or brown, globular or cylindrical, in the form of a spiral or of a tun, toothed or crenulate, with trenchant edge or pointed terminations; but, as a rule, our crustacean Diogenes houses itself in spirals of considerable length, as in Cerithium, Buccinum, or Murex.

The hermit is very timid; at the least noise it shrinks into its shell and squats itself, without motion, drawing in its smaller claws and closing the door with its larger ones, the latter being often covered with hairs, tubercles, or with teeth. In short, our prudent cenobite clings so closely to the bottom of its retreat, that we might pull it to pieces without getting it out entire; its tail is transformed into a sort of sucker, by the aid of which it attaches itself firmly to the walls of its habitation. It is at once strong and voracious, eating with much relish the dead fishes and fragments of molluscs and annelids which come in its way. Nor does it hesitate to attack and devour living animals. When introduced into an aquarium, it has sometimes thrown it into the utmost disorder by its insatiable rapacity. It has been possible sometimes to preserve harmony among many individuals inhabiting the same reservoir; but this has been owing rather to the impossibility of their attacking each other, in consequence of cunningly-devised barricades, than to their mildness of character or love of their neighbour. These animals, in short, are very quarrelsome. Two hermits cannot meet without showing hostility; each extends his long pincers, and seems to try to touch the other, much as a spider does when it seeks to seize a fly on its most vulnerable side; but each, finding the other armed in proof, and perfectly protected, though eager to fight, usually adopts the better part of valour, and prudently withdraws. They often have true passages of arms, nevertheless, in which claws are spread out, and displayed in the most threatening manner; the two adversaries tumbling head over heels, and rolling one upon the other, but they get more frightened than hurt. Nevertheless, Mr. Gosse once witnessed a struggle which had a more tragic end. A hermit crab met a brother Bernhard pleasantly lodged in a shell much more spacious than his own. He seized it by the head with his powerful claws, tore it from its asylum with the speed of lightning, and took its place not less promptly, leaving the dispossessed unfortunate struggling on the sand in convulsions of agony. "Our battles," says Charles Bonnet, "have rarely such important objects in view: they fight each other for a house."

A pretty little zoophyte, the Cloak Anemone (Adamsia palliata), loves to live with the hermit, and exhibits sympathies almost inexplicable. In aquariums this anemone attaches itself almost always to the shell which serves as the dwelling of the Crustacean; and it may be looked upon as certain that where the hermit is there will the anemone be found. These two creatures seem to live in perfect and intelligent harmony together, for Mr. Gosse's observations establish the existence of a cordial and reciprocal affection between them. This learned and intelligent observer describes the proceedings of a hermit which required a new habitation; he saw it detach, in the most deliberate but effective manner, its dear companion, the anemone, from the old shell, transport it with every care and precaution, and place it comfortably upon the new shell, and then with its large pincers give to its well-beloved many little taps, as if to fix it there the more quickly. Another species of Bernhardus makes a companion of the mantled anemone. "And we are assured," says Moquin-Tandon, "that when the crab dies its inconsolable friend is not long in succumbing also."

"Is there not here much more than what our modern physiologists call automatic movements, the results of reflex sensorial action?" says Gosse. "The more I study the lower animals, the more firmly am I persuaded of the existence in them of psychical faculties, such as consciousness, intelligence, skill, and choice; and that even in those forms in which as yet no nervous centres have been detected."

Lobsters.

In a dietary, as well as commercial sense, the lobster far excels the crab; like the latter, they have an amazing fecundity, each female producing from twelve to twenty thousand eggs in a season; and wisely is it so arranged, otherwise the consumption would soon exhaust them.

In France the size of the marketable lobster is regulated by law, and fixed at twenty centimètres (eight inches) in length; all under that size are contraband. Every year the inhabitants of Blainville proceed to Chaussey to fish for lobsters. They are taken in baskets in the form of a truncated cone, the mouth of which is so arranged that the animal can enter, but cannot get out. The numbers caught by each fisherman and his family in a season may be estimated at a thousand or twelve hundred, which realise to the family thirteen or fourteen hundred francs, the season lasting about nine months.

Lobsters are collected all round our own coast for the London market. On the Scottish shore they are collected and kept in perforated chests floating on the water, until they can be taken away to market. From the Sutherland coast alone six to eight thousand lobsters are collected in a season. This process goes on all round the coast, and as far as Norway, whence an enormous supply of the finest lobsters are obtained, for which something like £20,000 per annum is paid, all these contributions being conveyed to the Thames and Mersey in welled vessels. But these old-fashioned systems are being rapidly superseded by the construction of artificial storing ponds, or basins. Of these ponds Mr. Richard Scovell has erected one at Hamble, near Southampton, in which he can store with ease fifty thousand lobsters, which will keep in good condition for six weeks. Mr. Scovell's tank is supplied from the coasts of France, Scotland, and Ireland, where fine lobsters abound. He employs three large and well-appointed smacks, each of which can carry from five thousand to ten thousand. On the coast of Ireland alone, it is said, ten thousand fine lobsters a week might be taken.

The Lobster (Homarus) is found in great abundance all round our coast; frequenting the more rocky shores and clear water, where it is of no great depth, about the time of depositing its eggs. Various are the modes in which they are taken; cone-shaped traps made of wicker-work, and baited with garbage, are perhaps the most successful. These are sunk among the rocks, and marked by buoys. Sometimes nets are sunk, baited by the same material. In other places a wooden instrument, which acts like a pair of tongs, is used for their capture.

Mr. Pennant, the naturalist, paid great attention to the lobsters, and their habits are well described in a letter from Mr. Travis, of Scarborough. "The larger ones," he says, "are in their best season from the middle of October to the beginning of May. Many of the smaller ones, and some few of the larger individuals, are good all the summer. If they are four and a half inches long from the top of the head to the end of the back shell, they are called sizeable lobsters; if under four inches, they are esteemed half size, and two of them are reckoned for one of size. Under four inches they are called pawks, and these are the best summer lobsters. The pincers of one of the lobster's large claws are furnished with knobs, while the other claw is always serrated. With the former it keeps firm hold of the stalks of submarine plants; with the latter it cuts and masticates its food very dexterously. The knobbed or thumb claw, as the fishermen call it, is sometimes on the left, sometimes on the right side, and it is more dangerous to be seized by the serrated claw than the other."

There is little doubt that the lobsters cast their shell annually, but the mode in which it is performed is not satisfactorily explained. It is supposed that the old shell is cast, and that the animal retires to some lurking-place till the new covering acquires consistence to contend with his armour-clad congeners. Others contend that the process is one of absorption, otherwise, if there were a period of moult, it would be shown by their shells. The most probable conjecture is that the shell sloughs off piecemeal, as it does in the cray-fish. The greatest mystery of all, perhaps, is the process by which the lobster withdraws the fleshy part of its claws from their calcareous covering. Fishermen say the lobster pines before casting its shell, so as to permit of its withdrawing its members from it.

The female lobster does not seem to cast her shell the same year in which she deposits her ova, or, as the fishermen say, "is in berry." When the ova first appear under the tail, they are small and very black, but before they are ready for deposition they are almost as large as ripe elderberries, and of a dark-brown colour. There does not seem to be any particular season for this act, as females are found in berry at all seasons, but more commonly in winter. In this state they are found to be much exhausted, and by no means fit for the table.

The generic name, Astacus of Fabricius, is now confined to the crawfishes, which have a depressed rostrum, one tooth on each side, and the last ring of the thorax movable. The lobsters (Homarus) have the eyes spherical, two rings of the thorax being soldered together. The Norway Lobsters (Nephrops Norvegicus, Fig. 338) have the eyes uniform, and the two last rings of the thorax movable.

The last is one of the most beautiful of the larger Macrourans. Its general tint is pale flesh colour, with darker shades in parts, its pubescence light brown. This is generally considered a northern species, but Mr. Bell states that he has received specimens from the Mediterranean. It is found plentifully on the coast of Norway, on the Scottish coast, and in the Bay of Dublin. It is considered the most delicate of all the Crustaceans.

Before concluding this chapter, we perhaps should not omit brief notices of the common prawn (Palæmon serratus) and the shrimp (Crangon vulgaris), as types of an extensive variety of form of crustacea, which inhabit all seas, and which perform important functions as regards the sanitary state and economic condition of the waters of the ocean. These small animals are the scavengers of the sea—they pick up and devour all dead matter, leaving (it may be) a clean skeleton, without a shred of fibre behind. In this respect they resemble the ants on land, doing their work always thoroughly and effectively. We need hardly mention, what is so well known to every reader, that prawns and shrimps are amongst the most esteemed delicacies at our table, and as articles of food occupy no mean place on the fish-stall. At Billingsgate alone, it is hardly credible the immense quantities which arrive and are daily consumed in the Metropolis by all classes of the community. The shrimp, which although the smaller crustacean, is perhaps the finest flavoured of the two, is sold in much larger quantities than its more aristocratic congener, the prawn. The fishery of these savoury comestibles gives occupation not only to regular able-bodied fishermen, who devote themselves to this branch, but also to large numbers of women and children, who—with their baskets and small nets—may be seen plying their vocation in a multitude of well-known localities on our coasts, especially on the southern and south-eastern shores. To the habitués of Hastings, Southampton, Bognor, &c., there is not a more picturesque or familiar marine picture than to behold a troop of little shrimpers, in their grotesque and somewhat outré equipments, wading patiently knee deep all in a row, as they push before them their pole nets.

Without giving a detailed technical and anatomical description, which our space will not permit of, we may observe that the common prawn (Palæmon serratus) is about four or five inches long, with a rounded carapace, which is jointed and furnished at the head with numerous long antennæ, the eyes being large and round. The tail is broad and flat, the caudal laminæ of which are furnished with long hairs on the terminal margins. The animal is also furnished with several pairs of feet, very slender, and ordinarily bent within themselves.

The colour is light grey, spotted and lined with purplish shades. In the water, however, prawns are almost transparent, from the nearly entire absence of carbonate of lime in the carapace; they are thus very beautiful objects in the marine aquarium, moving as they do like shadows in the water.

When prawns are boiled, they become of a delicate pink colour, thus adding beauty to the dainty morceaux.

Like most other kinds of crustacea, the prawn is much larger in tropical climates. On the coast of South America, for instance, they attain a size of nine or ten inches in length, three of them being considered quite sufficient for a meal.

The London market is chiefly supplied with prawns from the Isle of Wight and Hampshire coast.

Like the prawn, the shrimp has many varieties. The common shrimp (Crangon vulgaris) is about two and a half inches long, from the eye to the extremity of the tail. It is also furnished with a rounded articulated carapace, with two antennæ. The eyes are prominent, marked, and near each other; the tail flat, laminated, and hirsute. The shrimp is not very unlike the prawn in general appearance, but is of a much less complex and finished structure.

In colour it is greyish brown, clotted all over with dark brown. In this species heat does not improve the colour.

This variety is one of the most abundant of all coast crustacea, swimming about and laying on the sands (which they closely resemble in colour) in immense shoals. Sometimes they are also found in deep water, but the margin of the sea is their favourite habitat. It may be added, that large quantities of the smaller palæmonidæ are caught with and sold as shrimps. Shrimps are in spawn all the year through, and cast their shells during the three months of spring.

The Entomostraca of Milne Edwards, or the Lophyropoda of Latreille, have no suctorial mouth or mandibles capable of mastication; their maxillæ are lamellose, and they have never more than ten swimming feet, and have from one to two eyes on stalks, and live in fresh water. There are two principal genera; the Copepoda of Edwards, and the Ostracoda. As a type of the first, we may mention Cyclops vulgaris (Leach), which, true to its name, has but one eye. But the genus Pontia of the same family has two. As a type of the second order, Ostracoda, we will specify the numerous family of the Cyprides, whose animals are enclosed in a bivalve shell, which causes their remains in Secondary strata to be classed with bivalve molluscs.

CHAPTER XVIII.

Fishes are intended to live always[14] in water, and this circumstance has impressed its seal upon their organization. Nevertheless, their forms are very varied; they are generally oblong, compressed laterally. They have no neck, the head being merely a prolongation of the trunk. In the majority of instances, the body is covered with scales, generally a thin bony substance developed out of the skin and overlapping each other, like the tiles of a roof.

Nothing is more remarkable than the variety and brilliancy of colour in fishes; they present almost every gradation, from golden or silver, and other dazzling colours, mingling with shades of blue, green, red, and black.

Fishes are essentially formed for swimming (Fig. 340), and all their members are adapted for this purpose. The anterior members, which correspond with the arms in man and the wings in birds, are attached to each side of the trunk, immediately behind the head, and form the pectoral fins. The posterior members occupy the lower surface of the body, and form the ventral fins. The latter, which are always over the ventral line, may be before, beneath, or behind the former. Fishes possess, besides, fins in odd numbers. The fins which erect themselves on the back are called the back or dorsal fins, those at the end of the tail are the caudal fins; finally, there is frequently another attached to the lower extremity of the body, which is called the anal fin. These fins are always nearly of the same structure, consisting generally of a fold of the skin, supported by slender, flexible, cartilaginous or osseous rays, connected by a thin membrane.

The muscles which bind together the vertebral column are so much developed in fishes as well as others of the superior animals, that they constitute in them alone the principal part of the body. The caudal, dorsal, and anal fins act as outlying oars; the pectoral and ventral fins assist in progression, at the same time that they help to maintain the equilibrium of the animal and guide and direct its movements, which are generally astonishing from their rapidity.

An organ, which belongs properly to fishes[15] (Fig. 341), and which is usually considered as their chief aid in swimming, is a large bladder situated within the body, between the dorsal spine and the abdomen. This is usually called the swimming bladder. According to the volume this bladder assumes, the animal can increase or diminish the specific gravity of its body; that is, it can remain in equilibrium or ascend or descend in the bosom of the waters; it is, moreover, remarked that it is very small in those species which swim at the bottom of the water, and Mr. Gosse says there is some reason for considering it to be the first rudimentary form of the air-breathing lung.

Immediately behind the head, two large openings are observed in most fishes; these are the gill-openings. Their anterior edge is mobile, and they are raised or lowered to serve the purposes of respiration; under this species of covercle are the gills, or branchiæ. These usually consist of many rows of thin membranous plates, hung on slender arches of bone, placed on each side of the head, usually protected by a bony plate made up of several pieces, called the gill-covers. The breathing is produced by water taken in at the mouth, which passes over the gill-membranes, and is ejected through an orifice at the hind margin of the gill-covers. During the contact of the water with the gills, the blood which circulates in these organs, and which communicates to them the red colour by which we recognize them, combines chemically with the oxygen of the air which the water holds in solution when it flows freely at the ordinary temperature in presence of the air. The blood is thus oxygenized, or made fit for respiration.

The heart in fishes is placed between the inferior parts of the branchial arch, and consists of a ventricle and an auricle (Fig. 342). It corresponds with the right half of the heart in the Mammifera and birds, for it receives the venous blood from all parts of the body and sends it to the gills. From this organ the blood is delivered into one great artery, which creeps along the vertebral column.

The eye in fishes is generally very large—we may even say enormous relative to the size of the head—and without true eyelids; the skin usually passes over the ocular globe, and becomes from this point so transparent that the luminary rays traverse it. This light covering is all the eyelid belonging to fishes. The interior of the eye is covered by the membrane called choroid, the thin external leaf of which, in consequence of the presence of innumerable microscopic crystals, presents the appearance of a gold or silver-coloured coating, which gives to the iris that extraordinary brilliancy which belongs to the fish's eye. The crystalline lens is voluminous, spherical, and diaphanous. When the fish is cooked, the crystalline lens constitutes that opaque and hard white substance which often comes under the teeth in eating fish of a certain size. Cuvier suspected, what anglers now know to be true, that those active chasseurs of the deep saw far and very clearly.[16]

If fishes have great eyes, they have, on the other hand, very small ears. This organ, it is found, has no exterior opening. It forms a cavity in the interior of the cranium, which is far from presenting the complicated structure of the ear in mammifers and birds. In spite, however, of the imperfect structure, fishes are sensible to the least noise. In consequence, silence is a rigorous law with the fisherman.

The dimensions of the mouth and teeth are very variable in fishes; these organs are in proportion to their voracity, which in many of these beings is very great. The form and development of the buccal pieces are also very various. Some species are toothless, but in most fishes the teeth are very numerous. They are sometimes attached, not alone to the two jaws, but also to the palate, to the tongue, and upon the interior of the branchial arch, and even in the back mouth, that is to say, upon the ospharyngeal, which surrounds the mouth of the œsophagus.

The form of their teeth is very variable both in arrangement and position: some are in the form of an elongated cone, either straight or curved. When small and numerous, they are comparable to the points of the cards used in carding wool or cotton. Sometimes they are so slender and dense as to resemble the piles of velvet, and often, from their very minute size, their presence is more easily ascertained by the finger than the eye. In some members of the Salmonidæ, for instance, we find a row of teeth on the bone that forms the middle ridge of the palate, which is called the vornex. On each side of this is another row on the palatine bones, and outside these is a third pair of rows on the upper jaw-bones. Some fishes have flat teeth, with a cutting edge in front of the jaws, like a true incisor; others have them rounded or oval, adapted to bruise or crush the various substances on which they feed.

The œsophagus connected with the mouth is short in fishes; the stomach and intestines vary in form and dimensions. Digestion is very rapid with these beings. Most of them feed on flesh, but there are a few where the mouth is without teeth, which feed on vegetables.

The growth of fishes is slow or very rapid, according to the abundance of food; they can suffer a very long fast, but in that state they become diminutive in size, and finally perish of exhaustion. At certain seasons an irresistible impulse brings the two sexes together. Many species whose ordinary appearance is dull and unsightly now shine in the most brilliant colours. The female soon after lays her eggs, the number of which passes all imagination. Nature seems to have accumulated in the body of each female myriads of eggs—a wise provision, which is rendered necessary by the numerous causes of destruction which threaten them in their native element. The eggs, abandoned by the females to the mercy of the waves, are fecundated after being deposited by the milt of the males. Such is a very brief summary of the organization of fishes, which have been briefly described as vertebrate, cold-blooded animals, breathing by means of gills; living in water, moving through the water by means of their fins, and reproducing their kind by means of eggs, or spawn. And now a few words on their classification.

Fishes naturally divide themselves into two series, according to the composition of their internal skeleton. This is usually osseous; nevertheless, a whole group of them constantly retain the cartilaginous or fibro-cartilaginous state. With some this frame presents even less power of resistance, and remains membranous.

It is precisely upon this peculiarity of structure that we found the great division of the class of fishes into two great groups of Cartilaginous and Osseous fishes, the first being again subdivided into three orders: namely, I. Cyclostomata, II. Selachia, III. Sturiona. The second into four orders: I. Plectognathii, II. Lophobranchii, III. Malacopterygii, IV. Acanthopterygii. Agassiz's system of classification of fish, founded on the form of the scales, is perhaps better suited than this to the palæontologist, but the one given above, founded as it is principally on the internal parts of the animal, is better suited to the zoologist. Agassiz's orders are the Ctenoid, type, Chromis, Placoid, Ganoid, and Cycloid.

CARTILAGINOUS FISHES.

Cartilaginous fishes are generally animals of considerable size, their structure ranging from ordinary fishes to eels. They are chiefly sea-fishes, only a few species being river-fishes. Naturalists divide them into two orders; namely, those having the gills free on the outer edge (the gilled Chondropterygeans), and those having these organs fixed on both edges. The first order comprehend three families: I. Cyclostomata, or Eels, Lampreys, &c., in which the mouth forms a sucker; II. Selachians, including Raias and Sharks, in which the mouth is furnished with jaws; III. Sturiona, or Sturgeons, which have the gills free.

I. Cyclostomata.

The first are characterised by the singular conformation of the mouth, which is formed for suction. The body is elongated, naked, and viscous, reminding us of serpents in their external form; they have neither pectoral nor ventral fins; their vertebræ are reduced to simple cartilaginous rings, scarcely perceptible one from the other, traversed by tendons, and covered by a second and more solid series of rings, which surround the soft cartilaginous spine. Their gills, in place of presenting the comb-like appearance of other fishes, have something of the form of a purse. The lampreys may be considered as the type of this family.

The Lampreys (Petromyzon) are cylindrical, with seven gill-openings on each side of the neck, forming two longitudinal lines; mouth round, armed with many teeth. The Sea Lamprey, P. marinus (Fig. 348), belongs to the Mediterranean; it is also found in the German Ocean, and the friend who supplies this note has caught it with cockle bait in the South Esk, Forfarshire. In the spring it ascends the rivers, where it is sometimes caught in abundance. Full-grown it is about three feet long, marbled brown upon yellow; the dorsal fins are separated by long intervals; its mouth is circular and surrounded by a fleshy lip, furnished with cirri, having a cartilaginous plate for support; it is provided on its internal surface with many circular rows of strong teeth, some single, the others double.

The Lamprey feeds on worms, molluscs, and small fishes; its mouth is a powerful sucker, by the aid of which it attaches itself to fishes often of great size, and sucks them like a leech. It is taken by hook and line, and speared by a sort of barbed harpoon, like the trident of the mythological Neptune, which is thrown, javelin fashion, at the animal when seen at the bottom of the water; the flesh is fat and delicate. In the twelfth century one of our kings, Henry I., surfeited himself at Elbeuf by partaking too largely of the Lamprey. The river-lamprey resembles the above in its general conformation, but is much smaller, and differs in the armature of the mouth, having only a single circular row of teeth. It is blackish above, silvery beneath, and is common in the markets of London and Paris, being frequently taken in the Seine. A smaller species, about ten inches in length, never leaves the fresh waters. It resembles the last species in colour, but its two dorsal fins are continuous; it is found in most European rivers and brooks. In some of the English rivers they are frequently taken in the eel-pots, weighing two and three pounds. They frequent stony bottoms, where they find small animals on which they feed. In its larva state it was long considered to be a distinct species of Ammocætes; it is now, however, ascertained that it only acquires its perfect form at the end of its second or third year.

II. Selachia.

The Selachians include a great number of cartilaginous fishes, varying much in form, including the rays, dog-fish, skate, torpedo, hammer-fish, sharks, and saw-fish; they have pectoral and ventral fins. On each side of the neck, on the lower surface, are five gill-openings, in form of a slit to each gill. Many of the species have two blow-holes in the upper part of the head. The order is divided into Raiadæ and Squalidæ.

RAIADÆ.

Of the Raiadæ there are several genera, and many species. In Cephaloptera the head is truncated, with large, lateral eyes. In Myliobates it is projecting, the pectoral fins extending like wings. In Trygon it is enclosed by the pectorals. In the Skate (Raia) the body is rhomboidal, tail without spine, but two small dorsals near the top. In the Torpedo the body is nearly round, the tail short and fleshy, with two dorsals and a caudal fin.

The White Ray, Raia batis (Fig. 349), reminds us of the lozenge shape, the point of the muzzle forming the lower angle, the longest ray of each pectoral forming the lateral angles, while the summit of the tail forms the last angle; the whole surface seems flat, but a swelling is distinguishable towards the head, on the upper surface, which bears, as it were, the contour of the body, properly so called, namely, the three cavities of the head, the throat, and the belly, which occupy the centre of the lozenge, beyond which the pectoral fins extend. These fins, though covered with a thick skin, permit the cartilaginous rays, with their articulations, to be very distinctly seen.