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Every mechanical power employed by man is at work in nature. There is as much skilful leverage in the human frame as in the most ingenious human machine. The pulleys by which heavy bodies are lifted from the ground do not give such clear indications of means and end, as the tendons and muscles by which the bones are moved. The mechanician has often a large cylinder running across or through his works, and to this he attaches the lesser parts of his machinery. Have we not a similar contrivance in the backbone of the higher animals, and the axis of the plant, constituting the support of all the appendages ? Every one who has seen the cord of plaited iron by which a carriage is dragged up an inclined plane, and has noticed how in it strength and flexibility are combined, should be prepared to admire the different means by which the same end is effected in the backbone of all animals, but especially in that of such animals as the eel and the serpent. The mechanician who wishes to combine the saving of materials and lightness with strength, makes his cylinder a hollow tube : it is on this principle that Messrs. Stephenson and Fairbairn bave spanned the Menai Straits by a tubular bridge ; but the principle was in operation before man adopted it, or was created to observe it, in the stems of grasses, and in many of the bones of animals, which are hollow. Found in the bones of all grades of living creatures, it is carried out to the greatest extent where most needed -in the bones of birds, so as to allow them to float in the air. In the case of birds, too, the air from the lungs permeates the larger bones as well as the smaller parts, the higher temperature of the body (108°-112° Fah.) rarefies it, and imparts an increased buoyancy to the whole frame.
Every joint in the animal frame can be shown to be exactly suited to the function which it has to perform. In flesh-eating animals, where strength is the chief requisite in the lower jaw, there is a simple hinge-joint of great power; whereas in herbivorous species, which have to grind hard vegetable matter, the joint admits of free motion in all directions. Where motion in one direction is all that is required, we have a common joint, as in the fingers; where motion all round is necessary, we have, as at the shoulder and hip, the ball-and-socket-joint, admitting of a rotatory 'motion round a ball. We have a beautiful example of ball-andsocket-joint in the sea-urchin, the spines of which have a cup-like cavity at the base, which is fitted to a converse tubercle on the shell, fixed by ligaments, and combining strength and great freedom of motion. In some parts of the animal frame, a single bone is all that is required, and more would injure the strength; in other parts, as in the fore-arm, a kind of rotatory motion is furnished by two bones, a radius and an ulna, so adjusted as to move to some extent round each other.
EVIDENCES OF DESIGN IN THE WORKS OF CREATION.
(Continued.) Almost every sort of instrument employed by man, has something resembling it in the operations of nature. The parts of the mouth of insects are made according to the instincts and habits of the animal, to act now as saws, now as knives, and, in the case of the leaf-cutting bees, the mandibles become scissors. The hyena is led by its instincts to crush the bones of carcasses and feed on them; and when certain teeth of that animal were shown by Professor Owen to an engineer, they were declared by him to be admirable models of hammers to break stones for roads.
The tongue of many shell-fish—that of the common limpet, for instance—has numerous silicious spines, and the organ is used as a rasp or drill. One end of the shell of Pholas resembles a file, and, by varied motions, the animal makes for itself tunnels in clay and in other substances. The foot of the mole is an admirable tunnelling instrument, and enables it to construct for itself those subterranean passages through which it is led, by its instincts, to wend its way in search of food.
Instruments of a more peculiar nature, and instruments invented by man only at a late date in the history of the race, have all along had their analogues in nature. Mill-stones are selected because they have gritty materials in the midst of softer substances; and we find that, on a like principle, soft and hard matters are mixed in the grinding-teeth of mammals. The cupping instruments of surgery were anticipated in the animal kingdom: the mouth of the leech combines in itself the offices of cupping-glass and scarificator; hence the importance of the animal as a remedial agent. It is also worthy of notice in regard to this animal, that the capacious stomach, with its lateral appendages or reservoirs, enables it to extract a very considerable quantity of blood before being detached. Some of the feet of a certain parasite * on various fresh-water fishes, are so modified that they act as real suckers or cupping-glasses : by a certain arrangement of muscles the animal can exhaust the cavity of its disc-like feet, and produce a vacuum, and is thus enabled to stick closely to the body of the fish.
The tubes and pipes which conduct water and gas through all the streets and dwellings of a great city, are not such ingenious contrivances as the veins and arteries which convey the blood to every extremity of the frame. The means by which water is forced to rise in a pump are not so wonderful as those by which, proceeding on a different principle, fluid is made to mount in the plant to the most distant twig and leaf. We construct valves to allow fluids. to pass in one direction, but to prevent them from flowing back in the opposite direction ; but before man devised such agency they were already in hi own veins; and it was upon noticing them that Harvey, proceeding, as he tells us, on the principle that they were there to serve a purpose, was led to the discovery of the circulation of the blood. In the back of the mouth of the crocodile are two cartilaginous plates or valves, one above, the other below; these, acting as flood-gates, cut off communication between the mouth and throat, so that the animal can hold its
prey underneath the water till dead, and itself continue all the while to breathe by its nostrils.
Among the most curious special modifications are those in which there is a provision made beforehand for the support of living creatures not yet in existence. Every one sees that there is foresight implied in parents laying up wealth to promote the future comfort of their children ; but there are equally clear evidences of forethought in the anticipations found among natural objects. In expectation of the birth of her child, the mother makes preparation for its clothing and comfort; but there has been a preparation by another Designing Mind, so as to cause the milk to flow at the very time at which it is required for the sustenance of the infant. In the case of animals developed from the egg, we find a store of nourishment laid up beforehand in the yolk, part of which is absorbed as food by the young chick or reptile. In the egg-cases of the common white whelk of our coasts, there is a further provision made for the sustenance of the young animal, in the form of a supplemental yolk, as it might be called. Each case, or capsule, contains several hundred bodies having the appearance of embryo, but only a small number in each capsule become living creatures. There can be no doubt, from Dr. Carpenter's observations, that these few are developed by the metamorphosis of the contents of their own yolks, but their growth or increase in size depends on the fact that they swallow and feed upon the additional or supplemental yolk.
* Argulus foliaceus.
Not only are the different parts of the animal and plant suited to each other, but there is a perfectibility about them—they are better adapted than anything else to the accomplishment of their end. There are examples of this which have now become commonplace by the eloquent expositions of them by Lord Brougham and others. Every principle followed by the skilful optician in the construction of artificial glasses has been attended to in the formation of the eye, and difficulties which long impeded the formation of perfect glasses were obviated all along in the structure of the natural organ. Bees build their honey-combs of double layers of hexagonal cells, and form the floors of their cells by three rhomboidal planes meeting at particular angles; and these have been shown, by high mathematical skill, to be the arrangements which combine the maximum of strength with the minimum of material. It is now said that this is produced by the compound eye of the bee being divided by hexagonal marks ; "and as the motions of the muscles of animals are directed very much by the mode of admission of light, the shape of the cells may be in accordance with that of the surface of the eyes.” Be it so, it is only a new illustration of the adjustment of natural instinct and the structure of an organ to produce an end which must have been contemplated, not by the intelligence of the bee, but of Him who gave to the bee its endowments. It has been shown, by mathematical investigation, that the shape of fishes is that which is best fitted to enable them to cleave their way through their native element.
It is a circumstance of great significance, that parts of animals which, to superficial observers, might seem useless, or even inconvenient, have been found, in the progress of discovery, to serve most important ends in the economy of life. The hump of the camel might readily be regarded as a very unseemly encumbrance, and we find even the distinguished naturalist, Buffon, speaking of these humps, and of the callous pads on the legs of that animal, as marks of degradation and servitude. A little patient investigation, however, suffices to show that these parts of their frame, like every other, fit these useful creatures for the purposes served by them in the regions which they inhabit. It has often been remarked, that the abundant supply of fluid laid up in the cells of one of the stomachs, is a beautiful provision for enabling the animal to endure a long continuance of thirst; and it can be shown that the enlargement of their feet, with their convex soles, allows them to tread easily on the loose, yielding sand of the desert; that the callosities or pads on their legs permit them to lie down and repose on scorching surfaces ; and that their humps are supplies of superabundant nourishment provided for their long journeys, so that, when deprived of other food, their frames feed on this nutriment,—and it has been observed, that at the close of a long journey their humps have been much diminished in size.
We are not surprised to find a man so proverbially vain as Buffon failing to discover marks of design in the hump of the camel; but it is rather wonderful to find Cuvier, whose heart was so filled with admiration of the divine wisdom, speaking somewhat doubtfully of the sloth. Its peculiar structure would, to use his language, have been inconvenient, if it had been intended that