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[graphic]

The same Egg as the preceding, with the external half of the vesicle

removed.

[graphic]

The Embryo of the preceding Egg, opened to show the course of the principal blood-vessels which go to the vesicle and to the areolar membrane. the thinness of their coats, they furnish the best object for demonstrating the circulation of the blood in a warm-blooded animal. According to Scarpa, the thigh-bones, when dried, now preserve their shape.

On the fourteenth day the feathers appear well developed; and if the embryo be taken out of the egg, it can open its beak for the purpose of breathing.

During the remaining part of the process, the yolk becomes gradually thinner and paler by the intermixture of the inner white; while an immense number of fringe-like vessels, with flaky terminations of a singularly peculiar structure, are formed on the inner surface of the yolk-bag, and hang into the

[graphic]

An Egg as it appears eighteen days after incubation.

[graphic]

The same Egg as the preceding, with part of the vesicle removed, to show the Embryo Chick more clearly.

[graphic]

The Embryo Chick opened to show the absorption of the yolk into the body.

yolk, evidently for the purpose of absorbing it and conveying it to the veins, where it is assimilated to the blood and applied to the nutrition of the chick. Blumenbach persuaded himself of the actual passage of the yolk from the floating vessels of the inner surface of the bag into the blood-vessels which go to the chicken; at least, he could distinguish yellow streaks in the red blood contained in the veins*.

On the nineteenth day the embryo can utter sounds, and may be heard doing so through the shell. Zool. Journal. ii, 433,

It breaks and escapes from the shell usually on the twenty-first day, but sometimes as early as the eighteenth, and at other times not till the twentyseventh.

[graphic]

An Egg as it appears twenty days after incubation. The vesicle and amnion are removed, to show the position of the perfect Chick.

The exit of the chick from the shell appears to us to be one of the most interesting processes of animated nature ever investigated by naturalists. We are indebted to Réaumur for a most minutely accurate account of this process*; and recently Mr. Yarrel has given a brief detail of his own observations upon several species of birds. It is the popular opinion, that the mother-bird breaks the shell of the egg to free the chick from imprisonment,-an opinion which must have originated from the circum

* Oiseaux Domestiques, Mém. vi.

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