structure and function in mammalian eggs 59 



Chemical Components 



Much attention has been given to the distribution in eggs of 

 basophilia and of the nucleic acids, the presence of which basophilia 

 is generally held to denote. As the oocyte grows, a perinuclear 



Fig. 50 

 Rat 8-cell egg as seen by dark-ground illumination, 

 showing distribution of granules. X 350. 



band of rna develops in the cytoplasm (Vincent and Dornfeld, 

 1948). During fertilization, the cytoplasm in sections of fixed rat 

 eggs showed evenly distributed weak basophilia, and strong acido- 

 philia. In 4-cell and 8-cell eggs, the intensity of the basophilia was 

 strongly augmented but was restricted in distribution chiefly to the 

 regions about the nuclei; acidophilic material, too, had a perinuclear 

 arrangement (Braden and Austin, 1953). Observations based on the 

 ultra-violet absorption of living rat eggs showed that, during 

 fertilization, moderately strong absorption was associated with the 

 irregular masses of granular elements, while the hyaloplasm showed 

 a lower absorption evenly spread throughout. With successive 

 cleavage divisions, the granular elements gathered more and more 

 about the nuclei, leaving the peripheral cytoplasm free (Fig. 50); 

 the absorption in the peripheral hyaloplasm tended to diminish 

 (Austin and Braden, 1953c) (Fig. 51). Absorption in the hyaloplasm 

 is probably attributable to rna, while that associated with granular 

 elements seems more likely to be due to mononucleotides. 



