wrinkled skin, clothed not in hair or gullet, or the stomach of fishes, such feathers, but defended by smooth and abstraction of air from the water is efglossy scales, lying as flat as possible, fected. Besides, the air contained in and with their free margin directed back this sac is a gas, which does not enter wards, all regularly overlapping each into the composition of water; and, moreother, like the slates of a roof. Besides over, it is not atmospheric air, which the this, the surface is lubricated by a mu- water has absorbed, and which it concous fluid, which in some, as in the eel, tains mingled with its proper particles. where the skin, from the extreme mi- In most instances, it is pure nitrogen; nuteness of the scales, appears naked, is but sometimes this gas is mixed with particularly abundant, and facilitates not oxygen, and in some cases the oxygen only the aquatic progression of the ani- predominates. Dr. Priestley was the mal, but enables it to creep through first who turned his attention to this small orifices, and insinuate itself into subject, and found that the air bag, or the holes, to which it retires for safety swimming bladder in the roach consisted, and concealment.

in some instances, of azote, or nitrogen, While we allude to the adaptation of unmixed ; in others, of nitrogen, with a these animals for the water, and to their small proportion of oxygen. Subseformation for traversing it, with the quently, Fourcroy pursued some experileast possible impediment arising from ments relative to the gas contained in their own structure, we are called upon the air bag, and found it in the carp to to notice an internal organ, respecting consist of almost pure nitrogen. Still which there have been many conjectures, more extensive and accurate experiments but which most naturalists consider to were undertaken by M. Biot; he found act the part of a float, enabling them to both nitrogen and oxygen in the air bag, rise with despatch from great depths, but he was unable to detach either carwhile at the same time it is so under bonic acid or hydrogen · He ascertained, control, as to permit them to re-descend, also, that the proportion of oxygen inwithout causing any obstruction. We creases, according to the depth at which allude to that apparatus commonly termed the fish habitually dwells; though in the the swimming-bladder, or sound. The sea water itself, whether taken from the swimming-bladder is an elongated mem- surface, or from the greatest depths posbranous sac, variable in form and extent, sible, there is no difference in the prorunning along the under surface of the portion of its constituents. More lately, spinal column, and firmly attached to it. (in 1809,) M. Configliacchi repeated M. It is filled with air, evidently the secre- Biot's experiments, and confirmed their tion of a delicate tissue, which lines it accuracy. It is then proved, that the internally. In many instances the swim- air contained in the apparatus in quesming bladder has no orifice, being closed tion, inasmuch as it is neither atmoentirely ; but in other instances, as the spheric air nor hydrogen, but usually salmon, sturgeon, herring, carp, etc., nitrogen; and moreover, as it is found the sac communicates with the æsopha- to fill the air sac, when this has no apergus, by means of an orifice, which allows ture, must be the product either of the the escape of the air, when the sac is lining membrane of the sac, or of a red compressed by the action of the abdo- glandular body within, which is someminal muscles. We have said, that the times extensive. air contained in this curious sac is se- In fishes, where the air bag has no creted by the apparatus itself; and this orifice or safety valve for the exit of the opinion is demonstrated by various facts. gas it contains, it is liable, under certain By some naturalists, indeed, it has been circumstances, to burst; as, for example, imagined, that the air was, in some un- when the fish is suddenly drawn up from accountable manner, abstracted by the a considerable depth into the air, and the fish from the surrounding water, and pressure of the water to which its body transmitted through the gullet into the had been subjected, instantaneously reair bag; but the impossibility of air moved, thereby allowing a rapid and being thus introduced, when no commu- energetic expansion of the previously nication exists between the guilet and compressed gas. This effect is frequently this air bag, is in itself at variance with produced on codfish, and even in perch such an hypothesis ; and besides, we and other fishes; and the gas rushing have yet to learn by what organ or ap- into the general cavity of the abdomen, paratus, either in the mouth or the not only distends it greatly, but even

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pushes up the gullet and stomach into the active mackarel are destitute of this the mouth.

air vessel, the conger and the common A question here suggests itself, Is the eel, which habitually reside at the botswimming bladder an organ which really tom of the water, and burrow in mud, deserves this appellation, as influencing are furnished with it, and it is often exthe fish in locomotion ?---in cleaving the tensively developed ; perhaps, indeed, water, either of the river, the lake, or but for its presence, the massive conger the sea ?-in sinking to the bottom, or would be unable to swim, or pursue its rising to the surface? There is con- prey. On the whole, the evidence is in siderable doubt on the subject. Some favour of the generally ascribed use of physiologists have supposed the appara- this air vessel ; but, as we have said, the tus in question to be in some way or theory is not quite satisfactory, as we canother an auxiliary to the gills or the not explain the reason why some fish, aëration of the blood: and others have habitually residing at the bottom of the advanced a step farther, and regarded it water, should have this organ, and others as the representative of the lungs of not; and why, while most fish which mammalia, or rather of birds, in which roam at various depths possess it, others latter the lungs are fixed to the vertebral equally active, and equally capable of column, and ribs ; but this is a visionary descending, or rising, should want it. speculation. Most regard it as an ap- It is from the air vessels, or sounds of paratus for altering the specific gravity various fishes, that isinglass is prepared. of the fish, and therefore of use in ena- Those of the codfish and the ling are bling the fish more easily to rise or de. frequently employed; but those of the scend. The compression of this sac, sturgeon are in the greatest request, and either by the muscles of the abdomen, furnish the best material. or of a special muscular apparatus acting The tenants of an element more dense upon it, will, of course, force the gas than our atmosphere, less capable of into a smaller space, the specific gravity conveying sound, or of transmitting rays of the fish increasing in a corresponding of light, often indeed turbid, from the ratio : and, on the contrary, the relax- admixture of extraneous matter, and ation of these muscles, the pressure being moreover but little adapted for the difthus removed, will allow the expansion fusion of odorous particles, fishes, as of the gus; and thus the specific gravity may be anticipated, have not the organs of the animal will become lighter: in of the senses so delicate, so refined, so the former case, its tendency will be to discriminating, as have the higher versink, in the latter to rise. Plausible as tebrata. Unlike mammalia and birds, this theory is, it is not quite satisfactory: which communicate their instinctive feelin favour of it, however, it may be ob- ings by cries and modulations of voice, served, that flat fish, such as soles, tur- these creatures are mute: many, besides, bot, etc., which reside always at the live at a depth where the roaring of the bottom of the water, are in general des billows, while the surface is tempesttitute of this air vessel; and further, that tost, cannot reach their realms of si. when in a fish possessing it, it is punc- lence; to such beings, a keen sense of tured, and the gas escapes, the ani- hearing would be useless. Accordingly, mal sinks immediately to the bottom, we find the auditory apparatus compaand is unable, by the exercise of its fins, ratively rude, (if the term be allowed) again to elevate itself. On the other and less developed than in birds and hand, there are many fishes which are mammalia. The whole organ, indeed, remarkable for their rapidity, and for lies deep beneath the skin, and is furthe facility of their movements, in which nished neither with an external ear, nor this apparatus does not exist. The sharks, a tympanic cavity, and, consequently, for example, which plunge down, and neither with a tympanum, (the drum of rise with extraordinary velocity, and the ear,) nor with the chain of little roam at various depths, are destitute of it. bones, which, in the higher verteThe common mackarel, (Scomber scom- brata, communicates between the tymber,) which is remarkable for activity, panum and the interior parts of the and which pursues its prey at the sur- labyrinth. There is, moreover, no Eusface, is not furnished with this appa- tachian tube. The ear of fishes, in fact, ratus, while in a very closely allied spe- consists only of a labyrinth, composed of cies (Scomber pneumatophoris) it is three semicircular canals, (a a a, in the present. But while the swift shark and following sketch,) communicating with a

a

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vestibule, b b, all membranous, and of the water in contact with their external lodged in a wide cavity on each side surface. That noise produces in fishes a

powerful sensation may be admitted ; but, as we have said, it is questionable, whether their ear appreciates differences of tone, as it does in birds and mammalia.

The olfactory organs of fishes probably possess a corresponding ratio of sensibility to those of hearing; and it appears to be rather by the sight than the smell that they search for or pursue their prey. We know that they seize artificial flies, and imitations of other fishes, of frogs, and of mice, etc., which, were they guided by the smell, they would not do. We are aware that some physiologists regard the sense of smell in these animals as very acute, and as furnishing them with a most important test, in their acquisition of food. Dr.

Munro (Comp. Anat. p. 127, 1783,) of the cranium, and surrounded im- says, “If you throw a fresh worm into mediately by a glassy mucilaginous the water, a fish shall distinguish it at a fluid: to each of these canals the audi- considerable distance; and that this is tory nerve c sends a filament, which ulti- not done by the eye is plain, from obmately spreads in the form of a beautiful serving, that after the same worm has network over the inner lining of the ves- been a considerable time in the water, tibule. The vestibule and the canals are and lost its smell, no fishes will come filled with a mucilaginous fluid, and the near it; but if you take out the bait, and former contains certain calcareous bo- make several little incisions into it, so as dies, of an enamel-like texture and ex- to let out more of the odoriferous efflutreme hardness, termed otolithes, or via, it shall have the same effect as forearstones, suspended by means of deli-merly. Now it is certain that, had the cate filaments; they are generally three creatures discovered this bait with their in number; their form differs greatly in eyes, they would have equally come to it the various species, but in every indivi- in both cases. In consequence of their dual of the same species they are them- smell being the principal means they selves the same.

have of discovering their food, we may In the cartilaginous fishes, as the frequently observe them allowing themshark, etc., these otolithes have neither selves to be carried down the stream, the enamel gloss, nor the hardness which that they may ascend leisurely against characterize them in other groups, and the current of the water; thus, the odothey resemble moistened starch, and riferous particles swimming in that meconsist of chalk, with a portion of gela- dium being applied more forcibly to tine.

their organs of smell, produce a stronger There is no cochlea, as in the human sensation." ear, into which the vestibule opens; and It is not, indeed, pretended, that fishes from this circumstance, and also from the do not use their smell in the selection of want of a tympanum, it is supposed that food, some, it is reasonable to conclude, these animals cannot distinguish the dif- more so than others; but it is certainly ferences of tone; that all sounds which not their principal means of discovering they do hear, are to them nearly the it. We have frequently watched trouts in a same, varying only in intensity, accord- river, motionless, with their head directed ing to the more or less violent vibration against the stream, and evidently watchof the fluid contained in the labyrinth, ing, not smelling, for their food; and and the agitation of the otolithes. But we have seen them not only dart at flies the vibration of this fluid must depend, settling on the surface, or at small fishes as there is no external orifice, upon the wandering near, but at an artificial fly vibrations of the walls of the cavity in which the angler has thrown within which the labyrinth is lodged, and these their reach ; we know, too, how passing walls must be affected by the vibrations clouds, throwing a fleeting shadow on

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the water, alarms them, how they retire | focus upon the retina, in a denser meif the angler renders himself conspicu- dium than the air, the power of the ous; how the weak avoid the strong, and crystalline lens is therefore increased to how the strong pursue the weak ;-—all the uttermost; and the aqueous humour, this involving sight, but not smell. Un- which being nearly of the same density like what we find in the higher verte- as the surrounding element, would have brata, the organs of smell do not com- but a feeble power in deflecting the rays municate with the back of the mouth; of light towards focus, is just a sufficithey consist of two cavities, near the an- ent quantity to allow of the free suspenterior part of the mouth, lined with a sion of the iris. The vitreous humour, fine mucous membrane, variously folded, moreover, though the rays of light passing in order to increase the extent of senti- through it are more refracted, than while ent surface, which is supplied by fila- passing through the aqueous, would still ments of the olfactory nerves. The be insufficient; and it is, therefore, that nostrils are simple orifices, for the ad- the crystalline lens is the chief agent in mission of the water, which, as there is bringing the rays to a focus on the reno outlet for it to pass through, immedi- tina. Instead of being simply convex, as ately after entering, remains longer than in terrestrial vertebrata, it is globular, does the air passing through the nasal | and though perfectly transparent, at the cavities of quadrupeds ; and hence the same time very dense. But as the focus succession of impressions on the olfac- of this lens will be short, in proportion tory organs of fishes is less rapid and to the increase of its refractive power, less changing

the approximation of the retina to it is With respect to the sense of taste, it is necessarily much closer than in mamconfessedly at a low degree: the tongue, malia ; and this approximation is accomthough supported by a large os hyoides, panied by a diminution of the vitreous is but imperfectly developed; it presents humour. Both the vitreous and the crysno distinct papilla, but is covered with talline lens are, in many fishes, kept in the same skin as that which lines the their place by a very delicate slender rest of the mouth; and often, indeed, membrane, derived from the retina, furnished with teeth. Fishes do not which traverses the vitreous humour, masticate their food, they seize it, and and is inserted into the capsular coverswallow it at once; they have no salivary ing of the lens. The structure of the glands.

lens of fishes, which has been recently The eye is the most important of the investigated by sir David Brewster, is organs of the senses which fishes are very curious. This philosophic investiendowed with. It enables them to per- gator found that the hard central portion ceive the approach of their foes, the of this globular body is composed of a presence of their food, and obstacles in succession of concentric, transparent, their course through the water. It is, spheroidal laminæ, the surfaces of which, however, as already intimated, easily de- though apparently smooth, have an irraceived by appearances ; and hence these diant lustre, as we see in mother-of-pearl, animals will bite at artificial flies, or ) and from the same cause, namely, the other lures, and even at a bit of red occurrence of regularly arranged lines, cloth, mistaking it for flesh. The eye

is or striæ. These lines, which mark the unprovided, as a general rule, with eye- edges of the separate fibres composing lids, but is capable of being slightly each lamina, converge from the meriturned in various directions, and is go- dian, as it may be called, of this globe, to verned by six muscles; as these animals the two poles: these fibres are flat, live in a fluid medium, with which the eye tapering as they approach the poles, or is always washed, they have no lachrymal parts of convergence; the breadth of the glands; but the cornea, which is slightly fibres of the external layer is about the convex, is protected by a delicate conti- 5,500th of an inch, and they are locked nuation of the common skin of the head together by an array of toothlike projecwhich passes over it. The sclerotic coat tions. The number of teeth in each fibre is of great thickness and firmness, and he computed to amount to 12,500. Now generally contains cartilaginous plates, the whole lens contains about 5,000,000 imbedded in its tissue; and in some of fibres; and, consequently, the total fishes, it is converted into a cap of bone. number of these minute teeth amounts As the eye in these aquatic creatures is to 62,500,000,000. The annexed rude adapted to bring the rays of light to a ! sketches show the arrangement of the

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fibres, and the appearance of their | in its structure, and envelopes the optic denticulations. As among other ani- nerve; it is of a deep red colour, but

its use is quite unknown: some have imagined it to be glandular, others muscular; but it seems rather to consist of a tissue of blood vessels.

We may now notice the respiratory organs of fishes, in connexion with the heart. The respiratory organs of fishes consist essentially of the gills, or branchiæ, which are defended externally, an operculum or gill lid, capable of being opened at pleasure, and when opened, exhibiting a wide semilunar fissure, la

terally seated between the head and mals, there is a very great difference body, on each side. In this great fissure, in the magnitude of the pupil of the

which freely communicates with the eye, and also of the eye itself. In one

mouth, the gills are placed ; but besides instance, that , namely, of the anableps, brane more or less developed, termed

the true operculum, there exists a memthere is a double pupil in each eye. the gill flap, or membrana brancheosFishes which reside in the depths of the ocean, from one to two or three hundred tega, supported by a series of slender fathoms below its surface, where the bones, arising from the os hyoides, or light of day scarcely reaches them, or

bone of the tongue: this gill flap forms which makes at most but an obscure the lower margin of the operculum, untwilight, have the eyes large, like those der which it is generally folded, and of nocturnal quadrupeds or birds; while which it assists in covering the gills. on the contrary, in such as live in mud, Being moveable, like a fin, independand burrow in the oozy slime of rivers, ently of the operculum, it may assist the or low shores, the eyes are small, and mouth, in throwing a current of water often rudimental ; in the myxines there over the gills, or it may effect this when are no traces of eyes.

The follow the mouth is occupied in seizing food : ing sketch will serve to show the

see sketch a, the operculum, or gill lid ;

b, the membrana brancheostega, or gill flap of the common herring. On raising

this apparatus, we see beneath it the general structure of the eyes as they gills, of a beautiful red colour, composed exist in the present class of animals : of cartilaginous arches, varying, in difa a, the sclerotic coat ; b b, the choroid ferent species, in the degree of their coat; cc, the retina, expanding from flexure, with their convexity posterior : the optic nerve, d ; é, the vitreous hu- this convexity is fringed with a series of mour; f, the crystalline lens, with its vascular fibrils, set like the plumelets membranous support; 9,

the aqueous composing the vane of a feather; and humour; h, the cornea; i, the continu- when minutely examined, they are found ation of the skin covering the cornea ; to be covered with a velvet-like memkk, a large body, between the choroid brane, over which myriads of wonderand the sclerotic, which is very vascular | fully minute blood vessels are spread, like