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In about twelve hours from the time the mother begins to sit, the commencement of life is perceptible in the germ (cicatricula). What seems to be

the head of the chick appears joined to the body and swims in the surrounding fluid; and towards the close of the first day this apparent head is seen bent back by its enlargement. So says Haller; but Blumenbach thinks this a deceptive appearance, produced only by the destined abode of the future chick, no trace of which, he says, is perceptible before the second day, when it assumes an incurvated form resembling a thread of jelly enlarged at the extremities, very closely surrounded by fluid, from which it is scarcely distinguishable. The first appearance of red blood is perceptible on the yolk-bag towards the end of the second day, a series of points being observed which form grooves; these closing consti

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An Egg as it appears sixteen hours after incubation, with a magnified view of the Embryo Chick,

frequently breed in orchard-trees, or even in the old stake of a fence, which they hollow out for the purpose. The great mass of hairs that cover the nostril appears to be designed as a protection to the front of the head when engaged in digging into wood.

The red-bellied woodpecker (Picus Carolinus) also digs a cavity for its nest, but seems anxious to procure all possible shelter from the weather by selecting the lower side of some lofty branch, that makes a considerable angle with the horizon. It prefers, however, a hollow limb of a tree, making the ex

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becomes the left ventricle; the third part (bulbus aorta) is considerably bulged out. It is remarkable that the heart at this period projects beyond the breast, and beats in triplets: first, on ceiving into the auricle the blood from the veins; secondly, on discharging this blood into the arteries; and thirdly, on forcing it into the vessels of the navel,-motions which will continue for twenty-four hours, if the embryo be taken out of the egg. The veins and arteries may now also be seen branching over the surface of the brain, and the spinal marrow beginning to extend along the back; or rather, as has been beautifully shown by Marcel de Serres*, Tiedemann †, and Carus, the spinal

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An Egg opened thirty-six hours after incubation, with a magnified view of the Embryo Chick, in which is shewn the first appearance of the principal blood-vessels.

*Du Cerveau, Paris, 1826; and Sur le Cervelet, Paris, 1823. + Geschichte des Gehirns des Foetus, 4to. Leipzig. Comparative Anatomy, by Gore.

marrow itself, becoming enlarged, forms the brain. At this period the fluid surrounding the foetus becomes more consistent and less transparent. About the same time also the spine, which was at first extended in a straight line, becomes bent, and the joints of the bone (vertebra) become distinct. The eyes are distinguished by their black pigment and comparatively large size, as they afterwards are in consequence of a peculiar slit in the lower part of the iris, a circumstance also observable in the nimble lizard (Lacerta agilis) and other animals which have no pupillary membrane.

On the fourth day the pupil of the eye can be distinguished as well as the aqueous and vitreous humours. In the head are perceived five vesicles, filled with a fluid; and these as they enlarge approach each other, coalesce, and form the brain, invested with its membranes. The wings also grow, the thighs begin

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An Egg opened four days after incubation, with a magnified view of the

Chick

to appear, and the body extends to one-third of an inch in length. Several other important organs now become visible, as the stomach, the intestines, and the liver. A vascular membrane begins to form about the navel, and grows during the succeeding days so rapidly that it covers almost the whole inner surface of the shell, apparently performing the office of lungs in carrying on the process of respiration.

On the fifth day the lungs begin to be formed, but cannot, of course, perform their functions, on account of the circumambient fluid. The vessels of the navel rise out of the abdomen; the heart is confined in a very thin membrane that covers the chest; and the muscles appear over the body in the form of an unctuous envelope.

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An Egg as it appears five days after incubation, with a magnified view of the Chick.

On the sixth day the gall-bladder is first perceptible, and the first indications of voluntary motion

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