Outlines of comparative physiology touching the structure and development of the races of animals, living and extinct - for the use of schools and colleges (1870) (14779663831)

Identifier: outlinesofcompar00agas (find matches)
Title: Outlines of comparative physiology touching the structure and development of the races of animals, living and extinct : for the use of schools and colleges
Year: 1870 (1870s)
Authors: Agassiz, Louis, 1807-1873 Gould, Augustus A. (Augustus Addison), 1805-1866 Wright, Thomas, 1809-1884
Subjects: Physiology, Comparative Zoology
Publisher: London : Bell & Daldy
Contributing Library: MBLWHOI Library
Digitizing Sponsor: MBLWHOI Library



Text Appearing Before Image:
, iaa viscous substance, generally colourless, but becoming opaquewhite on coagulation. Voluminous as it is in birds eggs, itnevertheless plays but a secondary part in the history of theirdevelopment. It is not formed in the ovary, like the yolk,but is secreted by the oviduct, and deposited around the yolkduring the passage of the egg through that canal. On thisaccount the eggs of those animals in which the oviduct iswanting, are generally destitute of albumen. In birds thealbumen consists of several layers, one of which, the cha-lazce (g, g),is twisted.Like theyolk, the al-bumen issurroundedby a mem-brane, theshell mem-brane (c\which iseither singleor double ;and in birds,as also insome rep-tiles andmollusca, isagain pro-tected by acalcareous
Text Appearing After Image:
covering,for min j; a Fig. 287.—Ideal section of an extruded hens egg, withslight alterations from Baer. (Entuickelung. der Thiere,B. I. Tab. III). A, blunt pole: B, sharp pole; a, a,shell; b, space filled with air ; c. membrane of the shell,which, at d, d, splits into two layers; e, e, limits of thesecond and thicker albumen; /, /, limits of the third andthickest albumen clinging to the chalazae ; g, a. chalaza?;h, yolk ; j, central cavity of the yolk, from which a canalor duct, &, leads to the cicatricula; I, cumulus prolige-rus ; m. germ (blastos). true shell (d). In most cases, however, this envelope continuesmembranous, particularly in the eggs of the mollusca, mostcrustaceans and fishes, salamanders, frogs, &c. Sometimes itis homv AS in the sharks and skates. 278 EMBEYOLOGY. SECTION II. DEVELOPMENT OF THE YOUNG WITHIN THE EGG. § 447. THE formation and development of the young animalwithin the egg is a most mysterious phenomenon. From ahens egg, for example, surrounded