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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 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 say, 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 determinen it. The meanest creature is a collection of wonders. The play of the rings in an earth-worm as it crawls; the undu latory motion propagated along the body; the beards of 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 roughness 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 was; muscular action, i.e. reciprocal contraction and rel axation being given, to describe how such an animal might be constructed, capable of voluntarily changing place Something, perhaps, like the organization of reptiles might have been hit upon by the ingenuity of an artist; or might have been exhibited in an automaton, by the combination of springs, spiral wires, and ringlets; but to the solution of the problem would not be denied, surely, the praise of invention and of successful thought: least of all could it ever be questioned, whether intelligence had been employed about it, or not.
* Contraction and expansion is the mode of progression in worms, but not in reptiles; in the class of serpents locomotion consists simply of repeated horizontal undulations, viz. flexion and extension. Thus the head being the fixed point, the body and tail assume several curves; the tail thou becomes the fixed point, the curvatures are straightened, and thus the animal advances with a serpentine motion. By these successive curvatures and right lines alternating, it moves forward at each step nearly the length of the whole body; the ribs, which Sir E. Home considers to act as feet, having nothing to do with locomotion unless as affording a fulcrum for the muscles.—Paacton
We have already considered relation, and under different views; but it was the relation of parts to parts, of the parts of an animal to other parts of the same animal, or of another individual of the same species. But the bodies of animals hold, in their constitution and roperties, a close and important relation to natures altogether external to their own; to inanimate substances, and to the specific qualities of these; e. g. they hold a strict relation to the ELEMENTs by which they are surrounded. I. Can it be doubted, whether the wings of birds bear a relation to air, and the fins of fish to water? They are instruments of motion, severally suited to the properties off the medium in which the motion is to be performed: ich properties are different. Was not this difference contemplated, when the instruments were differently constituted? II. The structure of the animal ear depends for its use, not simply upon being surrounded by a flûid, but upon the specific nature of that fluid. Every fluid would not serve: its particles must repel one another, it must form an elastic medium: for it is by the successive pulses of such a medium, that the undulations excited by the surrounding body are carried to the organ; that a communication is formed between the object and the sense; which must be done before the internal machinery of the ear, subtile as it is, can act at all. III. The organs of voice and respiration are, no less than the ear, indebted for the success of their operation to the peculiar qualities of the fluid in which the animal is immersed. They, therefore, as well as the ear, are constituted upon the supposition of such a fluid, i.e. of a fluid with souch particular properties, being always present. Chang : the properties of the fluid, and the organ cannot act; change the organ, and the properties of the fluid would be lost. The structure therefore, of our organs, and the properties of our atmosphere are made for one another. Nor does it alter the relation, whether you allege the organ to be made for the element, which seems the most natural way of considering it,) or the element as prepared for the organ. IV. But there is another fluid with which we have to do; with properties of its own; with laws of acting, and of being acted upon, totally different from those of air and water: and that is light. To this new, this singular element; to qualities perfectly peculiar, perfectly distinct and remote from the qualities of any other substance with which we are acquainted, an organ is adapted, an instrument is correctly adjusted, not less peculiar amongst the parts of the body, not less singular in its form, and in the substance of which it is composed, not less remote from the materials, the model, and the analogy of any other part of the animal frame, than the element to which it relates is specific amidst the substances with which we converse. If this does not prove appropriation, I desire to know what would prove it. Yet the element of light and the organ of vision, how ever related in their office and use, have no connexion whatever in their original. The action of rays of light upon the surfaces of animals, has no tendency to breed eyes in their heads. The sun might shine forever upon living bodies, without the smallest approach towards producing the sense of sight. On the other hand also, the animal eye does not generate or emit light. V. Throughout the universe there is a wonderful proportioning of one thing to another. The size of animals, of the human animal especially, when considered with respect to other animals, or to the plants which grow around him, is such, as a regard to his conveniency would have pointed out. A giant or a pigmy could not have milked goats, reaped corn, or mowed grass; we may add, could not have rode a horse, trained a vine, shorn a sheep, with the same bodily ease as we do, if at all. A pigry would have been lost amongst rushes, or carried off by hirds of rey. p It may be mentioned likewise, that the model and the materials of the human body being what they are, a much greater bulk would have broken down by its own weight. The persons of men who much exceed the ordinary stature, betray this tendency. - VI. Again (and which includes a vast variety of particalars, and those of the greatest importance;) how close is the suitableness of the earth and sea to their several in nabitants; and of these inhabitants, to the places of their appointed residence! Take the earth as it is; and consider the correspondency of the powers of its inhabitants with the properties and condition of the soil which they tread. Take the inhabitants as they are; and consider the substances which the earth yields for their use. They can scratch its surface, and its surface supplies all which they want. This is the length of their faculties! and such is the constitution of the globe, and their own, that this is sufficient for all their occasions. When we pass from the earth to the sea, from land to water, we pass through a great change; but an adeq'ite change accompanies us of animal forms and functions, of animal capacities and wants; so that correspondency remains. The earth in its nature is very different from the sea, and the sea from the earth; but one accords with its inhabitants - as exactly as the other. VII. The last relation of this kind which I shall mention is that of sleep to night; and it appears to me to be a relation which was expressly intended. Two points are manifest: first, that the animal frame requires sleep; secondly, that night brings with it a silence, and a cessation of activity, which allows of sleep being taken without interruption, and without loss. Animal existence is made up of action and slumber; nature has provided a season for each. An animal which stood not in need of rest, would always live in daylight. An animal which, though made for action, and delighting in action, must have its strength repaired by sleep, meets by its constitution the returns of day and night. In the human species, for instance, were the bustle, the labor, the motion of life, upheld by the constant presence of light, sleep could not be enjoyed without being disturbed by noise, and without expense of that time which the eagerness of private interest would not contentedly resign. It is happy therefore for this part of the creation, I mean that it is conformable to the frame and wants of their constitution, that nature, by the very disposition of her elements, has commanded, as it were, and imposed upon them, at moderate intervals, a general intermission of their toils, their occupations, and pursuits. But it is not for man, either solely or principally, that night is made. Inferior, but less perverted natures, taste its solace, and expect its return with greater exactness and advantage than he does. I have often observed, and
never observed but to admire, the satisfactio: no less than the regularity, with which the greatest part of the irrational world yield to this soft necessity, this grateful vicissitude: how comfortably the birds of the air, for example, address themselves to the repose of the evening; with what alertness they resume the activity of the day! Nor does it disturb our argument to confess, that certain species of animals are in motion during the night, and at rest in the day. With respect even to them, it is still true, that there is a change of condition in the animal, and an external change corresponding with it. There is still the relation, though inverted. The fact is, that the repose of other animals sets these at liberty, and invites them to their food or their sport. If the relation of sleep to night, and, in some instances, its converse, be real, we cannot reflect without amazement upon the extent to which it carries us. Day and night are things close to us; the change applies immediately to our sensations; of all the phenomena of nature, it is the most obvious and the most familiar to our experience; but in its cause, it belongs to the great motions which are passing in the heavens. Whilst the earth glides round her axle, she ministers to the alternate necessities of the animals dwelling upon her surface, at the same time that she obeys the influence of those attractions which regulate the order of many thousand worlds. The relation therefore of sleep to night, is the relation of the inhabitants of the earth to the rotation of their globe; probably it is more; it is a relation to the system, of which that globe is a part; and still farther, to the congregation of systems, of which theirs is only one. If this account be true, it connects the meanest individual with the universe itself: a chicken roosting jois its perch, with the spheres revolving in the firmanent. VIII. But if any one object to our representation, that the succession of day and night, or the rotation of the earth upon which it depends, is not resolvable into central attraction, we will refer him to that which certainly is, to he change of the seasons. Now the constitution of animals susceptible of torpor, bears a relation to winter, similar to that which sleep bears to night. Against not only the cold, but the want of food which the approach of winter induces, the Preserver of the world has provided in many animals by migration, in many others by torpor. As one example out of a thousand; the bat, if it did not sleep through the winter, must have starved, as the moths and flying insects, upon which it feeds, disappear. But the P