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This subject could easily be pursued further, and it might be shown, that, in various other particulars, there is an adaptation among the lower animals to the service of man, both among those which have already been domesticated, and such as remain wild. But it seems unnecessary; and I shall conclude by observing, that there may not improbably be various other tribes of the brute creation, which, at some future period, may be destined to swell the list of animals reclaimed by the art of man, and subservient to his use. Some of the properties I have mentioned, are certainly to be found among various orders which still roam the forest, pointing them out as subjects for an experiment, which, if successful, might confer a reciprocal boon.

ELEVENTH WEEK-SATURDAY.

FISHES.

Ir is not my intention to occupy much time in considering the inhabitants of the sea, which can scarcely be said to be affected materially by the seasons, as they live in an element where the sun exerts his influence less powerfully than either on the dry land or in the air, and where the changes from heat to cold are consequently less sudden. As these species of living beings, however, form a distinct department in the works of the Creator, and do not less remarkably exhibit his perfections than the other orders of the animal kingdom, it would be improper to pass them by, without some notice.

In reviewing the various series of animal existences, we constantly find that the simplest structures and modes of propagation are those belonging to the aquatic tribes. Among vertebrated animals, the lowest rank is occupied by Fishes,―a class comprehending an immense

number of species, which are all inhabitants of the water, which exhibit an endless variety of forms, and which open a wide field of interesting research. We cannot fail to perceive, on the most cursory glance, the beautiful adaptation of the form and structure of all these animals to the properties of the element in which they are destined to reside. In order that the fish might glide through the fluid with the least resistance, all its vital organs have been collected into a small compass, and the body has been reduced into the shape of a compact oval, compressed laterally, and tapering to a thin edge both before and behind, for the purpose of readily cleaving the water, as the fish darts forward, and also of obviating the retardation which might arise from the reflux of the water collected behind. With the view to diminish friction as much as possible, the surface of the body has been rendered smooth, and the skin has been impregnated with oil, which, while it lubricates the animal, defends it from injurious impressions, and, at the same time, prevents the water from penetrating into its substance.

The body of a fish is nearly of the same specific gravity as the water which it inhabits, and the effect of gravity is therefore almost counterbalanced by the buoyant force of that fluid. This is not, however, precisely the case, and as the body of a fish is generally a little heavier than the fluid medium, especially if it be fresh water, it is necessary for the animal to keep itself in some degree of motion in order to prevent its sinking. But there is here a very peculiar structure, which has justly been remarked as one of the most singular instances that is met with of an express contrivance for a specific purpose, and of the employment of an agency of a class different from that of the mechanical powers usually resorted to for effecting the same object. Were the animal to acquire the power of altering at pleasure its specific gravity, it would then possess the means of rising or sinking without calling into action either the

fins or the tail. Such is precisely the object of a peculiar mechanism which the Creator has provided in the interior of the body. A large bladder, filled with air, has been placed immediately under the spine, in the middle of the back, and above the centre of gravity. This is known by the name of the air-bladder, and is various in its form and structure in different fishes. When distended with air, it renders the whole fish specifically lighter than the surrounding water, and the animal is thus buoyed up, and remains at the surface without any effort of its own. On compressing the bladder by the action of the surrounding muscles, the included air is condensed, the specific gravity of the whole body is increased, and the fish sinks to the bottom. On relaxing the same muscles, the air recovers its former dimensions, and the fish is again rendered buoyant. Dr Roget, after describing this structure, significantly asks, "Can there be stronger evidence of design than the placing of this hydrostatic apparatus, acting upon philosophical principles, in the interior of the organization, for a purpose so definite and unequivocal ?"

There is assuredly something exceedingly striking in the peculiarity and admirable simplicity of this contrivance, but the evidence of design is not less complete in other parts of the construction of aquatic animals. Of this kind is the nature of the external mechanism for locomotion. The principal instrument of progression is the tail; for the fins are merely auxiliary organs, serving chiefly to balance the body. A fish moves in the water on the same principle as a boat is impelled in sculling or paddling, by striking rapidly with the tail alternately to the right and left. Every part of the body is calculated to promote the execution of this motion. The principal muscular strength is bestowed on the movements of the tail, and the most powerful muscles are those which give the lateral strokes just mentioned. For the same purpose the most important intestines are placed forwards, and crowded towards the head. There is no

neck; and the abdomen may be considered as immediately adjoining the head, the organs of respiration being placed rather below than behind the latter members. It is thus that scope has been given to the vertebræ connected with the motion of the tail, which compose more than half the bulk of the animal.

The construction above described is so admirably suited for its purpose, that most fishes glide through the water with the utmost rapidity, and with scarcely any visible effort, performing long journeys with no apparent fatigue. The salmon has been known to move at the rate of nearly four hundred miles a day, for many days together. Sharks often follow ships across the Atlantic, not only outstripping them in their swiftest sailing, but playing round them on every side just as if the vessels were at rest.*

Every thing about a fish is peculiar and specially adapted to the element in which it moves, the mouth, the gills, the fins, the circulation of the blood, the light and elastic gristle of the bones, the various organs of sense; and each in its kind forms a demonstration of consummate wisdom in the Divine Contriver. But I must not pursue the enticing subject further, and shall conclude with a striking passage from Mr Kirby's Bridgewater Treatise, in which he compares the tenants of the water with those of the air.

“When we sum up all the diagnostics of the class we are considering, we can trace at every step, so that almost he that runs may read, infinite power in the construction, infinite wisdom in the contrivance and adaptations, and infinite goodness in the end and object of all the various physical laws, and in all the structures and organizations by which they are severally executed, which strike the inquiring mind in this globe of ours. What else could have peopled the water and the air with a set of beings, so perfectly and beautifully in contrast with each other, as the fishes and the birds? * Roget's Bridgewater Treatise, vol. i., pp. 408, 434.

Sprung originally from the same element, they each move, as it were in an ocean of their own, and by the aid of similar, though not the same, means. The grosser element they inhabit required a different set of organs to defend, to propel, and guide, and to sink and elevate the fish from what were requisite to effect the same purposes for the bird, which moves in a rarer and purer medium. Yet as both were fluid mediums, consisting of the same elements, though differently combined, analogous organs, though differing in substance, structure and number, were required. For what difference is there between swimming and flying, except the element in which these motions take place? The fish may be said to fly in the water, and the bird to swim in the air; but perhaps the movements of the aquatic animal, from its greater flexibility and the number of its motive organs, is more graceful and elegant than those of the aerial. The feathers of the one are analogous to the scales of the other; the wings to the pectoral fins; and the tail of both acts the part of a rudder, by which each steers itself through the waves of its own element."*

Kirby's Bridgewater Treatise. vol. ii., pp. 375, 376.

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