STRUCTURE AND FUNCTION IN MAMMALIAN EGGS 63 



charged with alkaline phosphatase are produced in progressively 

 larger quantities, first around the nuclei and then throughout the 

 cytoplasm. For both substances, increase in amount is considered 

 to indicate active protein synthesis. Consistently, with regard to the 



Fig. 52 

 Pronucleus of the Chinese-hamster egg. X 1,200. 



rna increase, Alfert (1950) in the mouse and Skreb (1957) in the 

 bat reported that the cytoplasmic basophilia of the embryo becomes 

 strongly augmented at the time of implantation, particularly in the 

 inner cell mass. 



Organelles 



Mitochondria. The high content of mitochondria in eggs is 

 indicated by Gresson's (1940a) finding that, in the centrifuged oocyte 

 of the mouse, mitochondria (identified by staining with Janus Green 

 B) occupy one of the broadest of the zones that become separated. 

 Early oocytes bear, near the germinal vesicle, a distinctive structure 

 known as the yolk nucleus (Balbiani's body, corps vitellin, etc.) 

 which consists of the centrosome surrounded by a zone of clear 

 cytoplasm and around this lies a dense array of mitochondria and 

 argentophilic components of the Golgi complex (p. 64). As the 

 oocyte grows, the mitochondria spread out in small groups through 

 the cytoplasm and come to occupy the regions immediately around 

 the germinal vesicle and in the periphery of the cell. It is during 

 these changes that yolk formation predominantly occurs (see Van 

 der Stricht, 1923). During the pronuclear phase, mitochondria tend 



