322 HARRY H. CHARLTON. 



the ten or twelve cell stage before the degenerative processes 

 get the upper hand. 



The purpose of the present investigation is to describe step by 

 step the degeneration, whether it be fragmentation or partheno- 

 genetic development, of the unfertilized egg in the white mouse, 

 and to compare the process with follicular atresia in the mouse 

 and other mammals. 



The work was undertaken at the suggestion of Prof. W. R- 

 Coe, and done under his supervision. I am pleased to acknow- 

 ledge his many valuable suggestions during the course of the 



investigation. 



LITERATURE. 



Kingery ('14) describes the method of atresia in the follicles 

 of young mice. In his opinion the process is one of degenerative 

 fragmentation only, that the spindle fibers of the second matura- 

 tion spindle break, forming aster-like radiations and that later 

 the achromatic fibers entirely disappear. Then the loose 

 chromosomes form vesicles, and occasionally these fuse together 

 to form larger vesicles. This disturbs the nucleo-cytoplasmic 

 relationship, and an attempt to counter balance is made by the 

 cytoplasm breaking up and surrounding the nuclei, the larger 

 amount of cytoplasm enclosing the larger nuclear vesicles. In 

 some cases the cytoplasmic fragments have no nucleus whatever. 

 These fragments with or without nuclei are later absorbed, 

 probably by the action of phagocytic cells of follicular origin. 



Newman ('13) found that in the armadillo the first maturation 

 spindle was formed in the ovary and that the egg then waited 

 for ovulation. Eggs not located near the periphery of the 

 ovary were not ovulated. In such cases Newman found that 

 only a small percentage cut off the first polar body and that only 

 three per cent, in several hundred cases gave off the second 

 polar body, while ninety per cent, of the eggs were struck by a 

 process of follicular atresia, which is either a cytolysis or a 

 parthenogenetic development. He considers only the latter 

 contingency. In such eggs there is first a casting out of the 

 deutoplasmic mass from the formative cytoplasm. This he 

 considers to be an act of rejuvenation on the part of the dying 

 cell. Released from the burden of the yolk the cell is better 



