fore us under three divisions; feet, wings, and fins. The constitution of the elements, in which the motion is to be performed, is very different. The animal action must necessarily follow that consti-tution. Strip a wing of its feathers, and it bears no obscure resemblance to the fore-leg of a quadruped. But, fitted up with its furniture of feathers and quills, it becomes a wonderful instrument, more artificial than its first appearance indicates, though that be very striking; at least, the use which the bird makes of its wings in flying is more complicated, and more curious, than is generally known. The turning of the oar in rowing, whilst the rower advances his hand for a new stroke, is a similar operation to that of the feather. The steerage of a bird in its flight is effected partly by the wings, but in a principal degree by the tail.

From the wings of birds, the transition is easy to the fins of fish. In the case of fish, there is little or no weight to bear up; what is wanted, is only an impulse sufficient to carry the body through a resisting medium, or to maintain the posture, or to support or restore the balance of the body, which is always the most unsteady where there is no weight to sink it. For these offices the fins are as large as necessary, though much smaller than wings, their action mechanical, their position, and the muscles by which they are moved, in the highest degree con.venient. In most fish, beside the great fin the tail, we find two pairs of fins upon the sides, two single fins upon the back, and one upon the belly, or rather between the belly and the tail. The pectoral, and more particularly the ventral fins, serve to raise and depress the fish: when the fish desires to have a retrograde motion, a stroke forward with the pectoral fin effectually produces it; if the fish desire to turn either way, a single blow with the tail the opposite way sends it round at once: if the tail strike both ways, the motion produced by the double lash

is progressive, and enables the fish to dart forwards with an astonishing velocity. When the tail is cut off the fish loses all motion, and gives itself up to where the water impels it. The rest of the fins, therefore, so far as respects motion, seem to be merely subsidiary to this. In their mechanical use, the anal fin may be reckoned the keel; the ventral fins, out-riggers; and the pectoral muscles, the oars. In cetaceous or warm-blooded fish, which are obliged to rise every two or three minutes to the surface to take breath, the tail, unlike what it is in other fish, is horizontal; its stroke consequently perpendicular to the horizon, which is the right. direction for sending the fish to the top, or carrying it down to the bottom.

The superior sagacity of animals which hunt their prey, and which consequently depend for their livelihood upon their nose, is well known in its use, but not at all known in the organization which produces it.

The external ears of beasts of prey, of lions, tigers, wolves, have their trumpet part, or concavity, standing forwards, to seize the sounds which are before them, viz. the sounds of the animals which they pursue or watch. The ears of animals of flight are turned backward, to give notice of the approach of their enemy from behind, whence he may steal upon them unseen. The eyes of animals which follow their prey by night, as cats, owls, &c. possess a faculty not given to those of other species, namely, of closing the pupil entirely, for it was necessary for such animals to be able to descry objects with very small degrees of light. There appears to be also in the figure, and in some properties of the pupil of the eye, an appropriate relation to the wants of different animals. In horses, oxen, goats, sheep, and other grazing animals, the pupil of the eye is elliptical; the long axis being horizontal.

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LETTER LXXXIII.

Peculiarities of Animals.

MY DEAR CHILDREN,

We will now notice some peculiarities of structure which belong to quadrupeds, birds, and fish, as such, or to many of the kinds included in these classes of animals; and then, such particularities as are confined to one or two species.

Along each side of the neck of large quadrupeds, runs a stiff, robust cartilage, which butchers call the pax-wax. No person can carve the upper end of a crop of beef without driving his knife against it. It is a tough, strong, tendinous substance, braced from the head to the middle of the back: its office is to assist in supporting the weight of the head.

The oil with which birds prune their feathers, and the organ which supplies it, is a specific provision for the winged creation. On each side of the rump of birds is observed a small nipple, yielding upon. pressure a butter-like substance, which the bird extracts by pinching the pap with its bill. With this oil, or ointment, thus procured, the bird dresses its. coat; and repeats the action as often as its own sensations teach it that it is in any part wanted, or as the excretion may be sufficient for the expense.

The air bladder of a fish affords a plain and direct instance, not only of contrivance, but strictly of that species of contrivance which is a philosophical apparatus in the body of an animal. The principle of the contrivance is clear; the application of the principle is also clear. The use of the organ to sustain, and, at will, also to elevate the body of the fish in the water, is proved by observing, what has been tried, that when the bladder is burst the fish grovels at the bottom; and also, that flounders, soles, skates, which are without the air-bladder, seldom rise in the water, and that with effort. The man

ner in which the purpose is attained, and the suitableness of the means to the end, are not difficult to be apprehended. The rising and sinking of a fish in water, so far as it is independent of the stroke of the fins and tail, can only be regulated by the specific gravity of the body. When the bladder contained in the body of the fish is contracted, which the fish probably possesses a muscular power of doing, the bulk of the fish is contracted along with it; whereby, since the absolute weight remains the same, the specific gravity, which is the sinking force, is increased, and the fish descends; on the contrary, when, in consequence of the relaxation of the muscles, the elasticity of the enclosed and now compressed air, restores the dimensions of the bladder, the tendency downwards becomes proportionably less than it was before, or is turned into a contrary tendency. These are known properties of bodies immersed in a fluid. The enamelled figures, or little glass bubbles, in a jar of water, are made to rise and fall by the same artifice.

The fang of a viper is a clear and curious example of mechanical contrivance. It is a perforated tooth, loose at the root: in its quiet state, lying down flat upon the jaw, but furnished with a musele, which with a jerk, and by the pluck as it were of a string, suddenly erects it. Under the tooth, close to its root and communicating with the perforation, lies a small bag containing the venom. When the fang is raised, the closing of the jaw presses its root against the bag underneath, and the force of this compression sends out the fluid with a considerable impetus through the tube in the middle of the tooth.

The bag of the opossum is a mechanical contrivance, most properly so called. The simplicity of the expedient renders the contrivance more obvious than many others, and by no means less certain. A false skin under the belly of the animal forms a

pouch, into which the young litter are received at their birth; where they have an easy and constant access to the teats; in which they are transported by the dam from place to place; where they are at liberty to run in and out; and where they find a refuge from surprise and danger. It is their cradle, their asylum, and the machine for their conveyance.

The middle claw of the heron and cormorant is toothed and notched like a saw. These birds are great fishers, and these notches assist them in holding their slippery prey. The use is evident; but the structure such, as cannot at all be accounted for by the effort of the animal, or the exercise of the part. Some other fishing birds have these notches in their bills; and for the same purpose. The gannet, or Soland goose, has the side of its bill irregularly jagged that it may hold its prey the faster.

The stomach of the camel is well known to retain large quantities of water, and to retain it unchanged for a considerable length of time. This property qualifies it for living in the desert. Let us see, therefore, what is the internal organization, upon which a faculty so rare, and so beneficial, depends. A number of distinct sacks or bags, (in a dromedary thirty of these have been counted,) are observed to lie between the membranes of the second stomach, and to open into the stomach near the top by small square apertures. Through these orifices, after the stomach is full, the annexed bags are filled from it; and the water so deposited is, in the first place, not liable to pass into the intestines; in the second place, is kept separate from the solid aliment; and, in the third place, is out of the reach of the digestive action of the stomach, or of mixture with the gastric juice. It appears probable, or rather certain, that the animal, by the conformation of its muscles, possesses the power of squeezing back this water from the adjacent bags into the