M i c rons 



Figure 298. — Photomicrograph of a cross section of one follicle of a fully mature spermary of C. virginica. HematoxyJm- 



eosin. 



yolk forms 35 and 31 percent respectively of the 

 total egg volume. The estimates were obtained 

 after a centrifugal force of 20,000 {Cumiiujia) and 

 4,800 (Mytilus) times gravity had been applied 

 to the unfertilized eggs. In the cytoplasm of the 

 eggs of the two species the relative volumes of 

 hyaline zone were 42 and 55 percent and of the 

 oil 10 and 14 percent. 



The yolk of molluscan eggs is made of two 



types of granules, one of proteid and the other of 

 fatty materials. In cytological literature the 

 distinction between the proteid yolk and fatty 

 yolk is not always made clear. In descriptions of 

 the cytoplasmic inclusions of an egg based on 

 light microscopy some authors apply the term 

 exclusively to protein granules, while others, in- 

 cluding Gatenby (1919), Gatenby and Woodger 

 (1920), and Brambell (1924) in their studies of the 



EGG, SPERM, FERTILIZATION, AND CLEAVAGE 



329 



