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stance, that pieces of the shell are often broken and driven off to some distance, while the membrane within remains unruptured, which it is supposed could not happen if the fracture were made on the inside by the chick. But it might on the same principle be argued, that a wine-glass covered with parchment could not be broken by the stroke of a hammer without rupturing the parchment; for the membrane of the egg is elastic and yielding, while the shell is not. That the chicken, however, and not the mother, performs this office, has been proved by direct observations, which may be readily verified. It is worthy of remark, that the fact was correctly stated so long ago as the thirteenth century, by Albertus Magnus, the great naturalist of the dark ages *.

It might be supposed that this task was much above the strength of the yet feeble chick, did we not reflect that the anxiety it must feel to escape must add greatly to its energy, which is farther aided both by its peculiar structure, and by the position it assumes. The bill is still soft, indeed, and to a careless observer would seem ill fitted for breaking the shell; but, superadded to the bill, “ upon the curved part of the upper mandible," to use the words of Mr. Yarrel, "just above the point there will be seen a small horny scale, nearly circular, having at its centre a hard and sharp projecting point, and by the particular position of the head, this sharp point is brought into constant contact with the inner surface of the shell." It is worthy of remark, that the only use of this horny point seems to be to break through the shell, for when the chick escapes, and the beak hardens by exposure to the air, it soon falls off, and on the second or third day, only a light-coloured mark is observable on the spot which it had occupied. It may, indeed, be easily separated by the thumb-nail * Apud Aldrovand, Oruith, iii. 184, ed. Francofurti.

when the chick comes forth. In pigeons, and probably in other birds which do not run about and feed the instant they are hatched, the bill-scale does not fall off for more than a week. Mr. Yarrel thinks the hardness of the bill-scale may be proportioned to the thickness of the shell, from its being very prominent, hard, and sharp in a preserved chick of the Egyptian goose (Anser Gambensis).

The position of the chick in the egg appears no less unfavourable to its breaking through the shell than the softness of the bill; for it is rolled up almost like a ball, the neck sloping towards the belly, with the head in the middle, and the bill thrust under the right wing, as in birds when asleep. The feet also are bent up under the belly, as chickens and pigeons sometimes are when trussed for the spit, the claws being so bent back that their convex part almost touches the head. The forepart of the chick, as

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Réaumur observed, is towards the biggest end; and Dr. Prout adds, that it "is so situated in the egg, as, by its superior weight on one side, to assume such a position that the beak shall be uppermost It is surrounded by a thick strong membrane, which retains it in the attitude just described, and is apparently unfavourable to its requisite movements. But closer inspection shows that all these circumstances tend to facilitate rather than retard its operations on the shell, which it must break before it can escape.

The bill, indeed, though placed under the wing, as in the case of a sleeping bird, is thrust so far as to project beyond it towards the back, and the head, by moving backwards and forwards alternately, causes the bill to strike upon the shell, the action being partly guided by the wing and the body. It is to be

Phil. Trans. for 1822.

remarked, that the head, compared with the bulk of the body, is very heavy; and it makes, together with the neck, a load which the chick, even for several days after its exclusion, can with difficulty support. But in the egg, let the position be what it may, the head is supported either by the body or by the wing, or by both together; and the greater the size of the head, the more efficient of course are the blows of the bill. The length of the neck causes it to be bent at this time, though after the first fourteen days it becomes nearly straight; but what seems to be done out of necessity to procure room, is here, as in many other operations of nature, the best thing that possibly could have been done out of choice.

By watching at the proper time, Réaumur frequently heard chicks hammering upon the shell with their beaks; and in the more advanced stages of the operation he could actually see them at work, through the translucent membrane. The result of the first strokes is a small crack, commonly situated nearer the larger than the smaller end of the egg. When this crack is perceptible, the egg is said to be chipped. The membrane is seldom ruptured in the first instance, even when the hard part of the shell over it is detached; but in one instance, while Réaumur was observing the operations of a chick by candle-light, it was hard at work pecking at the membrane divested of its shell. It did not strike, however, but seemed as if endeavouring to wear it out, and make it thinner by continued friction.

The continued blows extend the first cracks, and new pieces of shell are driven off almost all in the same circle, the blows running round nearly the whole circumference of a circle which never cuts the egg obliquely, but always directly across; yet the bill all the while remains under the wing, and always in the same position. In order to accomplish this,

it is indispensable for the chick to turn gradually round, till it has completed an entire revolution; though this eircumstance cannot, in consequence of the opacity of the shell, be actually observed. The demonstration of the inference, however, is completed by the several places at which the point of the bill appears, whilst the head is kept constantly under the same wing; a position so strictly preserved, that it is persisted in even for some time after the separation of the shell into two portions, leaves the chick a door almost as large as the dimensions of his prison. The revolution which the chick thus makes on his own body is invariably from, left to right, and it is probably performed by means of the feet; for the claws, on pressing the shell through the membrane that separates them from it, must find in that shell the resistance necessary to effect the required circular motion. This notion is corroborated by the circumstance of the feet alone enabling the chick to effect its exit; for the wings and other members, with the exception of the neck and bill, are incapable of any action so long as the chick is in the shell. Réaumur, being curious to ascertain the mode of the circular movement of the chick, was not contented with mere probability, but had recourse to experiment.

"Is it," he asks, " contrary to probability that the strokes of the bill upon the shell exert a reaction on the body of the chick sufficient to alter its position, and turn it by little and little round the circle? A plain experiment seemed to me well adapted to determine this; founded on the principle, that if the notion was correct, the chick could not turn itself if the bill were so placed as to have nothing solid to press against, a condition easily produced, by taking from the bill that solid support against which it was supposed necessary for it to act, or protracting the

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