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mals, and an amphibious way of life, partly in the air, and partly on the land and waters, so is their body accordingly shaped, and all their parts incomparably fitted for that way of life and motion; as will be found by a cursory view of some of the particulars. And the
1. First and most visible thing, is the shape and make of their body, not thick and clumsy, but incomparably adapted to their flight: sharp before, to pierce, and make way through the air, and then, by gentle degrees, rising to its full bulk. To which we may add,
2. The neat position of the feathers throughout the body; not ruffled, or discomposed, or placed some this, some a contrary way, according to the method of chance; but all artificially placed for facilitating the motion of the body, and its security at the same time, by way of clothing: and for that end, most of the feathers tend backward, and are laid over one another in exact regular method, armed with warm and soft down next the body, and more strongly made, and curiously closed next the air and weather, to fence off the injuries thereof. To which purpose, as also for the more easy and nimble gliding of the body through the air, the provision nature hath made, and the instinct of these animals to preen and dress their feathers, is admirable; both in respect of their art and curiosity in doing it, and the oil-bag* glands and whole apparatus for that service.
And now, having said thus much relating to the body's motion, let us, 3. Survey the grand instrument thereof, the
* Mr Willoughby saith there are two glands for the secretion of the unctuous matter in the oil-bag. And so they appear to be in geese. But upon examination, I find, that in most other birds (such at least as I have inquired into) there is only one gland : in which are divers little cells, ending in two or three larger cells, lying under the nipple of the oil-bag. This nipple is perforated, and being pressed, or drawn by the bird's bill, or head, emits the liquid oil, as it is in some birds, or thicker unctuous grease, as it is in others.
wings,—which, as they are principal parts, so are made with great skill, and placed in the most commodious point of the
to give it an exact equipoise in that subtile medium, the air.
And here it is observable, with what incomparable curiosity every feather is made; the shaft exceeding strong, but hollow below for strength and lightness sake; and above, not much less strong, and filled with a parenchyma or pith, both strong and light too. The vanes are nicely gauged on each side as made; broad on one side, and narrower on the other; both which incomparably minister to the progressive motion of the bird, as also to the union and closeness of the wing.+
And no less exquisite is the textrine art of the plumage I
* In all birds that fly much, or that have the most occasion for their wings, it is manifest that their wings are placed in the very best part, to balance their body in the air, and to give as swift a progression as their wings and body are capable of. For otherwise, we should perceive them to reel, and fly unsteadily; as we see them do if we alter their equipoise by cutting the end of one of the wings, or hanging a weight at any of the extreme parts of the body.
of The wise Author of Nature hath afforded an example of the great nicety in the formation of birds, by the nicety observed in a part no more considerable than the vanes of the flag-feathers of the wing. Among others, these two things are observable. 1. The edges of the exterior or narrow vanes bend downwards, but of the interior, wider vanes upwards; by which means they catch hold, and lie close to one another, when the wing is spread, so that not one feather may miss its full force and impulse upon the air. 2. A yet lesser nicety is observed, and that is in the very sloping the tips of the flag-feathers. The interior vanes being neatly sloped away to a point, towards the outward part of the wing; and the exterior vanes, towards the body, at least in many birds; and in the middle of the wing, the vanes being equal, and but little sloped. So that the wing, whether extended or shut, is neatly sloped and formed, as if constantly trimmed with a pair of scissors.
I Since no exact account that I know of, hath been given of the mechanism of the vanes or webs of feathers, my observations may not be unacceptable. The vane consists not of one continued membrane, because if once broken, it would hardly be reparable ; but of many laminæ, which are thin, stiff, and somewhat of the nature of a thin quill. Towards the shaft of the feather (especially in the shaft-feathers of the wing) those laminæ are broad, &c., of a semicircular form, which serve for strength, and for the closer shutting of the laminæ to one another, when impulses are made upon the air. Towards the outer part of the vane, these laminæ grow slender and taper. On their under side they are thin and smooth, but their upper outer edge is parted into two hairy edges, each side having a different sort of hairs, laminated or broad at bottom, and slender and bearded above the other half. I have, as well as I could, represented the uppermost edge of one of these laminæ with some of the hairs on each side, magnified with a microscope. These bearded bristles or hairs on one side the laminæ, have straight beards; those on the other side, have hooked beards on one side the slender part of the bristle, and straight ones of the other. Both these sorts of bristles magnified (only scattering and not close) are represented as they grow upon the upper edge of the laminæ. And in the vane, the hooked beards of one lamina always lie next the straight beards of the next lamina, and by that means lock and hold each other, and by a pretty mechanism brace the laminæ close to one another. And if at any time the vane happens to be ruffled and discomposed, it can by this pretty easy mechanism be reduced and repaired.
also; which is so curiously wrought and so artificially interwoven, that it cannot be viewed without admiration, especially when the eye is assisted with glasses.
And as curiously made, so no less curiously are the feathers placed in the wing, exactly according to their several lengths and strength: the principals set for stay and strength, and these again well lined, faced, and guarded with the covert and secondary feathers, to keep the air from passing through, whereby the stronger impulses are made thereupon.
And lastly, to say no more of this part, that deserves more to be said of it, what an admirable apparatus is there of bones, very strong, but withal light and incomparably wrought! of joints, which open, shut, and every way move, according to the occasions either of extending it in flight, or withdrawing the wing again to the body! and of various muscles; among which the peculiar strength of the pectoral muscles deserves especial remark, by reason they are much stronger in birds than in man, or any other animal not made for flying.
4. Next the wings, the tail is in flight considerable; greatly assisting in all ascents and descents in the air; as also serving to steady* flight, by keeping the body upright in that subtile and yielding medium, by its readily turning and answering every vacillation of the body.
And now, to the parts serving for flight, let us add the nice and complete manner of its performance; all done according to the strictest rules of mechanism. What rower on the waters, what artist on the land, what acutest mathematician, could give a more agreeable and exact motion to the wings, than these untaught flying artists do theirs ? serving not only to bear their bodies up in the air, but also to waft them along therein with a speedy progressive motion, as also to steer and turn them this way and that way, up and down, faster or slower, as their occasions require, or their pleasure leads them.
5. Next to the parts for flight, let us view the feet and legs ministering to their motion : both made light for easier transportation through the air; and the former spread, some with membranes for swimming, some without, for steady going, for
Mr Willoughby, Ray, and many others, imagine the principal use of the tail to be to steer, and turn the body in the air, as a rudder. But Borelli hath put it beyond all doubt, that this is the least use of it, and that it is chiefly to assist the bird in its ascents and descents in the air, and to obviate the vacillations of the body and wings. For, as for turning to this or that side, it is performed by the wings and inclination of the body, and but very little by the help of the tail.
of It is considerable in all water-fowl, how exactly their legs and feet correspond to that way of life. For either their legs are long, to enable them to wade in the waters : in which case their legs are bare of feathers a good way above the knees, the more conveniently for this purpose. Their toes also are all broad; and in such as bear the name of Mudsuckers, two of the toes are somewhat joined, that they may not easily sink in walking upon boggy places. And as for such as are whole-footed, or whose toes are webbed together (excepting some few) their legs are generally short, which is the most convenient size for swimming. And ’tis pretty enough to see how artificially they gather up their toes and feet when they withdraw their legs, or go to take their stroke; and as artificially again extend or open ;ا
perching, for catching and holding of prey,* or for hanging by the heels to gather their food,+ or to fix themselves in their places of retreat and safety. And the latter, namely, the legs, all curved for their easy perching, roosting, and rest, as also to help them upon their wings in taking their flight, and to be therein commodiously tucked up to the body, so as not to obstruct their flight. In some long, for wading and searching the waters; in some of a moderate length, answerable to their vulgar occasions; and in others as remarkably short, to answer their especial occasions and manner of life. To all which let us add the placing these last-mentioned parts in the body. In
their whole foot, when they press upon, or drive themselves forward in the waters.
* Some of the characteristics of rapacious birds, are to have hooked, strong, and sharp-pointed beaks and talons, fitted for rapine, and tearing of flesh; and strong and brawny thighs for striking down their prey. Willoughby Ornith., l. 2. c. 1. Raii Synops. Av. Method. p. 1.
+ Such birds as climb, particularly those of the woodpecker kind, have for this purpose (as Mr Willoughby observes, 1. 2 c. 4)—1. Strong and musculous thighs. 2. Short legs, and very strong. 3. Toes standing two forwards, and two backwards. Their toes also are close joined together, that they may more strongly and firmly lay hold on the tree they climb upon. 4. All of them have a hard stiff tail, bending also downwards, on which they lean, and so bear up themselves in climbing.
I Swifts and swallows have remarkably short legs, especially the former, and their toes grasp anything very strongly; all which is useful to them in building their nests, and other such occasions as necessitate them to hang frequently by their heels. But there is far greater use of this structure of their legs and feet, if the reports be true of their hanging by the heels in great clusters (after the manner of bees) in mines and grottos, and on the rocks by the sea, all the winter-of which latter, I remember the late learned Dr Fry told his story at the university, and confirmed it to me since, viz. :That an ancient fisherman, accounted an honest man, being near some rocks on the coast of Cornwall, saw at a very low ebb, a black list of something adhering to the rock, which when he came to examine, he found it was a great number of swallows, and, if I misremember not, of swifts also, hanging by the feet to one another, as bees do, which were covered commonly by the sea-waters, but revived in his warm hand, and by the fire. All this the fisherinan himself assured the doctor of.