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calculated to counteract the effects of repletion. «
Or there may be cases, in which a defect is artificial, and compenfated by the very cause which produces it. Thus the JJoeep, in the domesticated state in which we see it, is destitute of the ordinary means of desence or escape; is incapable either of resistance or flight. But this is not so with the wild animal. The natural sheep is swift and active: and, if it lose these qualities when it comes under the subjection of man, the loss is compenfated by his protection. Perhaps there is no species of quadruped whatever, which sufsers so little as this does, from the depredation of animals of prey.
For The Sake of making our meaning better understood, we have considered this business of compenfation under certain particularities of constitution, in which it appears to be most conspicuous. This view of the subject necessarily limits the instances to single species of animals. But there are compenfations, perhaps, not less certain, which extend over large classes, and to large portions, of living nature.
I. In quadrupeds, the deficiency of teeth is usually compensated by the faculty of rumination. The sheep, deer, and ox tribe, are without fore teeth in the upper jaw. These ruminate. The horse and ass are furnished with teeth in the upper jaw, and do not ruminate. In the former class the grass and hay descend into the stomach, nearly in the state in which they are cropped from the pasture, or gathered from the bundle. In the stomach they are softened by the gastric juice, which in these animals is unusually copious. Thus softened, and rendered tender, they are returned a second time to the action of the mouth, where the grinding teeth complete at their leisure the trituration which is necessary, but which was before left impersect. I fay the trituration which is necessary ; for it appears from experiments that the gastric fluid of iheep, for example, has no effect in digesting plants, unless they have been previously masticated; that it only produces a slight maceration, nearly as common water would do in a like degree of heat: but that, when once vegetables are reduced to pieces by mastication, the fluid then exerts upon them its specific operation. Its first effect is to soften them, and to destroy their natural consistency:
it then goes on to dissolve them; not sparing even the toughest parts, such as the nerves of the leaves *.
I think it very probable that the gratification also of the animal is renewed and prolonged by this faculty. Sheep, deer, and oxen, appear to be in a state of enjoyment whilst theyv are chewing the cud. It is then, perhaps, that they best relish their food.
II. In birds, the compensation is still more striking. They have no teeth at all. What have they then to make up for this severe want? I speak of graminivorous and herbivorous birds; such as common fowls, turkeys, ducks, geese, pigeons, &c. for it is concerning these alone that the question need be asked. All these are furnished with a peculiar and most powerful muscle, called the gizzard; the inner coat of which is fitted up with rough plaits, which, by a strong friction against one another, break and grind the hard aliment, as effectually, and by the fame mechanical action, as a coffee-mill would do. It has been proved by the most correct experiments, that the gastric juice of these birds will not operate
? Spal. Diss. III. sec. cxl.
x 4 upon upon the entire grain; not even when softened by water or macerated in the crop. Therefore without a grinding machine within its body; without the trituration of the gizzard; a chicken would have starved upon a heap of corn. Yet why should a bill and a gizzard go together? Why should a gizzard never be found where there are teeth?
Nor does the gizzard belong to birds as such. A gizzard is not found in birds of prey. Their food requires not to be ground down in a mill. The compenfatory contrivance goes no further than the necessity. In both classes of birds however, the digestive organ within the body, bears a strict and mechanical relation to the external instruments for procuring food. The soft membranous stomach, accompanies the hooked, notched, beak; the short, muscular legs; the strong, sharp, crooked talons: the cartilaginous stomach, attends that conformation of bill and toes, which restrains the bird to the picking of seeds or the cropping of plants.
III. But to proceed with our compensations. A very numerous and comprehensive tribe of terrestrial animals are entirely without feet; yet locomotive; and, in a very considerable derable degree, swift in their motion. How is the want of feet compensated? It is done by the disposition of the muscles and fibres of the trunk. In consequence of the just collocation, and by means of the joint action of longitudinal and annular fibres, that is to fay, of strings and rings, the body and train of reptiles are capable of being reciprocally shortened and lengthened, drawn up and stretched out. The result of this action is a progressive, and, in some cases, a rapid movement of the whole body, in any direction to which the will of the animal determines it. The meanest creature is a collection of wonders. The play of the rings in an earth-worm, a^ it crawls; the undulatory motion propagated along the body; the beards or prickles, with which the annuli are armed, and which the animal can either shut up close to its body, or let out to lay hold of the roughnesses of the surface upon which it creeps; and the power arising from all these, of changing its place and position, affords, when compared with the provisions for motion in other animals, proofs of new and appropriate mechanism. Suppose that we had never seen an animal move upon the ground without feet, and that the problem