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regard to volume and weight, as to suit exactly the wants of the animal in its station, and to act as a mutual counterpoise, so that it should not be overswayed by the preponderance of one organ over another; every thing proving that the momentum and action of each, both independently, and in concert with the rest, had been nicely calculated before its creation, by one whose Wisdom knew no bounds, whose Will was the well being and well doing of his creatures, each in its place, and whose Power enabled him to give being to what his Wisdom planned, and his Will decreed:

Nothing is more graceful ånd elegant than the motions of fishes in their own pure element. Not to mention the shifting radiance of their forms, as they glance in the sunbeams; their extreme flexibility, and the ease with which they glide through the waters, gives to their motions a character of facile progress which has no parallel, unless, perhaps, in the varied flight of the wing-swift swallow, amongst their analogues, the birds. How rapidly do they glide, and are lost to our sight by a mere stroke of their tail! at another time, less alarmed, how quietly do they suspend themselves, and cease all progressive motion, so that we can discover them to be alive only by the fan-like movement of their pectoral fins, an action, which seems, in some sort connected with their respiration; for they move them, as I have observed, more rapidly, when, in sultry weather they seek the surface, and their muzzle emerges. These fins, the analogue, as has been before observed, of the hand or fore foot, except in a few instances, may be regarded as usually the first pair of oars that propel the vessel. Some fishes, in front of these, have another locomotive organ and weapon, not intended, however, for motion so much in the water as on the earth; this is a powerful, and, usually, serrated bone, articulating with the shoulder bones, and is to be found in the Siluridans, with the exception of the electric species, which its Creator has fitted with other arms.

2

The second pair of fins, as they most commonly occur, are the ventral, but sometimes, where fishes have a large head, they are placed forwarder, and in general they are under the most bulky part of the body; by this arrangement, we may gather that they are intended to counteract the force of gravity, as well as to act as oars. These fins are wanting in all the

1 PLATE XII. FIG. 1. a. 2.

2 N. B. The figure of the bone (2) in the Plate was taken from one dug up in this neighbourhood in formimg a manure heap, which Mr. Owen informed me belonged to a Silurus.

fishes called, on that account apodes, or footless, to which the eels, and other serpentine fishes belong, some of which also have no pectorals.

The caudal or tail fin, which directs the locomotions of fishes as a rudder, and gives to them the chief part of their force and velocity, in the majority of real fishes is vertical, but in flatfish which have no natatory vesicle, it is horizontal, as it is likewise in the Cetaceans and Amphibians; in all these, its motion is vertical.

The dorsal is also a powerful fin, consisting of spiny rays; in some tribes, as the perch, though wanting in others, it is sometimes divided into two or three fins. By its various undulations, and by the differently inclined planes which it presents to the water, this fin augments the means of fishes to move in any direction, and adds much to the speed with which those last named pursue their prey: it counterhalances the effect of the caudal fin in cross-currents; but if the animals could not depress it, it might occasionatly destroy the equilibrium, and overset them.

The anal fin seems, in many fishes, intended as an antagonist to the dorsal, to prevent the above effect and maintain the fish in its due position.

But fins were given to fishes not only to be the instruments of motion in their own element, but likewise in that of terrestrial animals; to some they were given to enable them, under particular circumstances, to vie with the birds in their aërial flights; to others, that like quadrupeds, they may undertake excursions upon Terra firma; and to a third description, amongst other means, to assist them in climbing the trees in quest of their food. Every body knows that the pectoral fins of the different species of flying fishes are very long; that by them, when leaping out of the water to avoid the pursuit of their enemies, the bonito,' and other rapacious fishes, they are supported in the air for a short time; but the action is really not. flying, since they use these fins merely as an aëronaut, in descending, uses a parachute, for a support in the air; in fact, flying from aquatic enemies, they are soon attacked by aërial ones, and the frigate, and other marine birds, make them their prey-so that they take short flights, as well as short voyagesand though they swim rapidly, they are soon tired, which is the means of saving those that escape from their numerous enemies, and preventing the extinction of the race. Besides the

1 Scomber Pelami.

2 Tachypetes Aquila.

common flying-fish,' the Pegasus, a small fish, inhabiting the Indian ocean, when pursued, leaps out of the water, and takes a short flight.

3

I mentioned on a former occasion, the terrestrial excursions of the Hassar, and from the statement of Piso, in his Natural History of the Indies, published in 1658, and from that of Marcgrave, of Brazil, quoted by Linné in the Amanitates Academica, it appears that the Callicthys migrates in the same way. Dr. Hancock mentions a fish, perhaps a Loricaria, which has a bony ray before the ventral as well as the pectoral fins, and which creeps on all fours upon the bed of the rivers, perhaps even when they are dry. These little quadruped fishes must cut a singular figure upon their four stilts.

I have given a full account of a climbing fish amongst the migratory animals, and shall therefore now take my leave of the finny tribes.

Perhaps the fins of the Cetaceans and Amphibians, above described, inasmuch as they are enveloped not in a membrane, like the fins of fishes, but are real feet adapted to their element, may be regarded as more analogous to what are called paddles, by which term the natatory apparatus of the Chelonian reptiles, and of the marine Saurians, hitherto found only in a fossil state, are distinguished. These in the former, the turtles, are formed by the legs and toes being covered by a common skin, so as to form a kind of fin, the two first toes of each leg being armed with a deciduous nail. The coriaceous turtle, the parent of the Grecian lyre, which presents no small analogy to the Amphibians, has no scales either upon its body or feet, but both are covered with a leathery skin, even its shell resembling leather, and therefore it connects the paddles. of the Chelonians with those of the marine Mammalians. It may be defined as a natatory organ, formed of several jointed digitations, covered by a common leathery or scaly integument. In the fossil Saurians the paddle appears to be formed of numerous bones arranged in more than five digitations, but it is shorter and smaller, and seems better calculated for still waters and a waveless sea than to contend with the tumultuous fluctuations of the open ocean.

Next to the paddles of the turtles, and fossil Saurians, come

1 Exocatus exiliens in the Mediterranean, and E. volitans in the ocean,

but doubts are said to rest upon this species.

2 P. Draco, volans, &c.

4 I. 500. t. xi. f. 1.

6 See above, p. 65.

3 See above, p. 64.

5

PLATE XII. FIG. 1. 7 Sphargis coriacea.

8 See Philos. Trans. 1816. t. xvi. and 1819. t. xv.

the palmated or web-foot of the aquatic tortoises, and of numerous oceanic birds, in which the toes are united by a common skin. In the paddle the leg and toes together form the natatory organ; in the palmated, or lobed foot, the toes. Thus from fins we seem to have arrived at digitated legs.

Wings.-Turning from the denser medium of water, we must next inquire what organs have been given to animals by their Creator, to enable them to traverse the rarer medium of air, to have their hold upon what to the sight appears a nonentity, and to withstand the fluctuating waves of the atmospheric sea, and the rush of the fierce winds which occasionally sweep through space over the earth. The name of wings has by general consent been given, not only to the feathered arm of the bird, but also to those filmy organs extended, and often reticulated, by bony vessels-the longitudinal ones in some degree analogous to the rays of the fins of the fishes, especially of the flying fishes-which so beautifully distinguish the insect races; as well as to the rib-supported membrane forming the flying organs of the dragon; and those hand-wings by which the bats with so much tact and such nice perception steer without the aid of their eyes through the shrubs, and between the branches of trees; those also of other mammiferous animals, such as the flying squirrel and flying opossum use in their leaps from tree to tree.

Savigny is of opinion that certain dorsal scales, in pairs, observable in two of the genera1 of his first family of Nereideans, are analogous to the elytra and wings of insects: this he infers from characters connected with their insertion, dorsal position, substance and structure, but not with their uses and functions; for, as he also states, they are evidently a species of vesicle, communicating by a pedicle with the interior of the body, which, in the laying season, is filled with eggs, a circumstance in which they agree with the egg-pouches of the Entomostracans; and therefore Baron Cuvier's opinion, that there is little foundation for the application of this term to these organs seems to me correct.

Wings may be divided into organs of flight and organs of suspension. The first are found in insects, in which they are distinct from the legs; in birds, in which the anterior leg of

1 Halithea and Polynoe. See Aphrodita Clava. Montague in Linn. Trans. ix. 108, t. vii. f. 3.

2 Aphrodite.

4 Regn. Anim. iii. 206.

3 Syst. des Annel, 27.

quadrupeds becomes a wing; and in bats and vampyres, in which both the anterior and posterior legs support a wing.

She second kind of wings is found in the flying cat, the flying squirrel, and the flying opossum; and, under a different form, in the flying dragon of modern zoologists.

The wings of insects differ materially from those of birds, and of certain Mammalians: for instance, the bats and vampyres, since in them they are not formed by skin or membrane, attached to the fore-leg, or both legs, but are distinct organs implanted in the trunk, usually leaving, the animal its classical number of legs, for its locomotions on terra firma. These organs are composed of two membranes, closely applied to each other, and attached to elastic nervures issuing from the trunk, and accompanied by a spiral trachea or air-vessel. These nervures vary in their number and distribution: in some insects the wing has none except that which forms its anterior margin,' and in others the whole wing is reticulated by them;" the longitudinal ones often give an inequality to the surface, and form it into folds, which probably, in flight, it can relax or contract according to circumstances, in some genera3 the wing is folded longitudinally in repose, and in others also transversely. In the higher animals the wings never exceed a single pair; but in insects the typical number is four; and though some are called Dipterous, or two-winged, yet even a large proportion of these have, in the winglets, the rudiment of another pair. The anterior pair, called elytra, &c., in the beetles, and some others, are principally useful to cover and protect the wings when unemployed, still they produce some effect in flight, and they partake, in a reduced degree of the motion of the wings, those of the cock-chaffer describing an arc equal to only a fourth part of that of the latter organs.

M. Jurine, in which he is followed by M. Chabrier, has regarded the primary wing of insects as analogous to the wing of birds; but though this may hold good in some respects, it does not in its main feature. If we consider that the wing of birds is really the analogue of the fore-leg of quadrupeds, and replaces it; and also that insects have a representative of that leg fixed to the anterior segment of the trunk, thence called the Manitrunk, in contradistinction to the Alitrunk, which bears the wings; it seems not probable that the anterior leg, and the anterior wing which belong to different segments, should

Psilus, &c, See Jurine Hymenopt. t. v. and xiii. G. 48.
Libelluline.

1

2

5 Alule.

3 Vespida.
6 Melolontha vulgaris.

4 Cleoptera.

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