OF THE EGG 



2/7 



the lien's egg. or by its outline, when the yolk itself is trans- 

 parent, as in the eggs of fishes and mollusca. It contains one 

 or more little spots, somewhat opaque, appearing as small dots, 

 the ffprmhtaf dots (<?). On closer examination, these dots are 

 themselves found to contain still smaller nucleoli. 



44t). The albumen, or white of the egg (fig. 287, e, e), is 

 a viscous substance, generally colourless, but becoming opaque 

 white on coagulation. Voluminous as it is in bird's eggs, it 

 nevertheless plays but a secondary part in the history of their 

 development. It is not formed in the ovary, like the yolk, 

 but is secreted by the oviduct, and deposited around the yolk 

 during the passage of the egg through that canal. On this 

 account the eggs of those animals in which the oviduct is 

 wanting, are generally destitute of albumen. In birds the 

 albumen consists of several layers, one of which, the cha- 

 (y, 



is twisted. 

 Like the 

 yolk, the al- 

 bumen is 

 surrounded 

 by a mem- 

 brane, the 

 shell mem- 

 brane (c), 

 which is 

 either single 

 or double ; 

 and in birds, 

 as also in 

 some rep- 

 tiles and 

 mollusca, is 

 again pro- 

 tected by a 

 calcareous 

 covering, 

 forming a 

 true shell (d 



Fig. 287. Ideal section of an extruded hen's egg, with 

 slight alterations from Bae'r. (Entwickelung. der Thiere, 

 B. I. Tab. III). A, blunt pole ; B, sharp pole ; a, a, 

 shell ; 6, space filled with air ; c, membrane of the shell, 

 which, at d, d, splits into two layers ; e, e, limits of the 

 second and thicker albumen ; /,/, limits of the third and 

 thickest albumen clinging to the chalazae ; g, g, chalazfe ; 

 h, yolk ; ?', central cavity of the yolk, from which a canal 

 or duct, , leads to the cicatricula ; I, cumulus prolige- 

 rus ; m, germ (blastos). 



In most cases, however, this envelope continues 

 membranous, particularly in the eggs of the mollusca, most 

 crustaceans and fishes, salamanders, frogs, &c. Sometimes it 

 is horny, as in the sharks and skates. 



