Outlines of comparative physiology : touching the structure and development of the races of animals, living and extinct for the use of schools and colleges / by Louis Agassiz and A.A. Gould ; edited from the revised ed. and greatly enl. by Thomas Wright.
- Louis Agassiz
- Date:
- 1855
Licence: Public Domain Mark
Credit: Outlines of comparative physiology : touching the structure and development of the races of animals, living and extinct for the use of schools and colleges / by Louis Agassiz and A.A. Gould ; edited from the revised ed. and greatly enl. by Thomas Wright. Source: Wellcome Collection.
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![to it from the yolk ; when the incubation has advanced con- siderably, the albumen loses almost the whole of its water and salts; these seem to be transferred to the yolk, which admits of explanation, for the vitellary sac bursts and draws the albumen, now changed into a thick mass, into it. By this accession of matter, the yolk enlarges during the first half of the period of incubation, but becomes thinner; the incessant demand upon it, however, for materials for the growth of the embryo, causes it again to shrink and to become more consis- tent towards the end of the period (§ 494). The proportion of chemical elements of the vitellus and white vary consider- ably ; the quantity of phosphorus contained in the albumen lessens, but increases in the yolk, and again appears in com- bination with oxygen and calcium as a phosphate of lime, which in the period of ossification is plentifully required for the consolidation of the bones ; as tlie quantity of lime contained in an egg at the time it is laid is extremely small, and becomes very large at a subsequent period, the earth must be acquired in some way with which we are not at present well acquainted. As it is not very probable that the lime is derived from the shell, it may perhaps be produced from other matters under the influence of the organic agencies ; the same may be said of the iron, the quantity of which increases greatly during incubation.] * * The whole of this article on the development of the chick is from Professor Wagner, Elements of Physiology, p. 84, et secj. It forms a valuable complement to the chapter on Embryology.—Ed.](https://iiif.wellcomecollection.org/image/b28056644_0371.jp2/full/800%2C/0/default.jpg)
