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downward; whereas those which proceed from the side towards the beginning, or quillend of the feather, are shorter, firmer, and turn upwards. The process then which takes place, is as follows: when two laminæ are pressed together, so that these long fibres are forced far enough over the short ones, their crooked parts fall into the cavity made by the crooked parts of the others; just as the latch that is fastened to a door, enters into the cavity of the catch fixed to the doorpost, and there hooking itself, fastens the door; for it is properly in this manner, that one thread of a feather is fastened to the other.
This admirable structure of the feather, which it is easy to see with the microscope, succeeds perfectly for the use to which nature has designed it; which use was, not only that the lamine might be united, but that when one thread or lamina has been separated from another by some external violence, it might be reclasped with sufficient facility and expedition*
In the ostrich, this apparatus of crotchets and fibres, of hooks and teeth, is wanting :
* The above account is taken from Memoirs for a Natural History of Animals, by the Royal Academy of Paris, published in 1701, p. 219.
and we see the consequence of the want. The filaments hang loose and separate from one another, forming only a kind of down; which constitution of the feathers, however it may fit them for the flowing honours of a lady's head-dress, may be reckoned an imperfection in the bird, inasmuch as wings, composed of these feathers, although they may greatly assist it in running, do not serve for flight.
But under the present division of our subject, our business with feathers is, as they are the covering of the bird. And herein a singular circumstance occurs.
In the small order of birds which winter with us,
from a snipe downwards, let the external colour of the feathers be what it will, their Creator has universally given them a bed of black down next their bodies. Black, we know, is the warmest colour: and the purpose here is, to keep-in the heat, arising from the heart and circulation of the blood. It is further like , wise remarkable, that this is not found in larger birds; for which there is also a reason :-small birds are much more exposed to the cold than large ones; forasmuch as they present, in proportion to their bulk, a much larger surface to the air. If a turkey were divided into a number of wrens (supposing the shape of the turkey and the wren to be
similar), the surface of all the wrens would exceed the surface of the turkey, in the proportion of the length, breadth (or, of any homologous line), of a turkey to that of a wren; which would be, perhaps, a proportion of ten to one. It was necessary therefore that small birds should be more warmly clad than large ones: and this seems to be the expedient, by which that exigency is provided for.
II. In comparing different animals, I know no part of their structure which exhibits greater variety, or, in that variety, a nicer accommodation to their respective conveniency,
than that which is seen in the different formations of their mouths. Whether the purpose be the reception of aliment merely, or the catching of prey, the picking up of seeds, the cropping of herbage, the extraction of juices, the suction of liquids, the breaking and grinding of food, the taste of that food, together with the respiration of air, and, in conjunction with it, the utterance of sound; these various offices are assigned to this one part, and, in different species, provided for, as they are wanted, by its different constitution. In the human species, forasmuch as there are hands to convey
the food to the mouth, the mouth is flat, and by reason of its flatņess, fitted only for reception:
whereas the projecting jaws, the wide rictus, the pointed teeth of the dog and his affinities, enable them to apply their mouths to snatch and seize the objects of their pursuit. The full lips, the rough tongue, the corrugated cartilaginous palate, the broad cutting teeth of the ox, the deer, the horse, and the sheep, qualify this tribe for browsing upon
pasture; either gathering large mouthfuls at once, where the
grass is long, which is the case with the ox in particular; or biting close, where it is short, which the horse and the sheep are able to do, in a degree that one could hardly expect. The retired under-jaw of a swine works in the ground, after the protruding snout, like a prong or plough-share, has made its way to the roots upon which it feeds. A conformation so happy, was not the gift of chance.
In birds, this organ assumes a new character; new both in substance and in form ; but in both, wonderfully adapted to the wants and uses of a distinct mode of existence. We have no longer the fleshy lips, the teeth of enamelled bone: but we have, in the place of these two parts, and to perform the office of both, a hard substance (of the same nature with that which composes the nails, claws, and hoofs of quadrupeds) cut out into proper
shapes, and mechanically suited to the actions which are wanted. The sharp edge and tempered point of the sparrow's bill picks almost every kind of seed from its concealment in the plant; and not only so, but hulls the grain, breaks and shatters the coats of the seed, in order to get at the kernel. The hooked beak of the hawk-tribe separates the flesh from the bones of the animals which it feeds upon, almost with the cleanness and
precision of a dissector's knife. The butcherbird transfixes its prey upon the spike of a thorn, whilst it picks its bones. In some birds of this class, we have the cross-bill, i. q. both the upper and lower bill hooked, and their tips crossing. The spoon-bill enables
to collect its food from the bottom of pools, or to seek it amidst the soft or liquid substances with which it is mix. ed. The long tapering bill of the snipe and woodcock, penetrates still deeper into moist earth, which is the bed in which the food of that species is lodged. This is exactly the instrument which the animal wanted. It did not want strength in its bill, which was inconsistent with the slender form of the animal's neck, as well as unnecessary for the kind of aliment upon which it subsists; but it wanted length to reach its object.