FATE OF UNFERTILIZED EGG IN WHITE MOUSE. 327 



have separated from their spindle position and lie scattered in 

 the cytoplasm. One of the chromosomes shows the beginning 

 of vesicle formation, which is seen completed in Fig. 9. Fig. n 

 shows essentially the same condition. The polar body has 

 divided and several small phagocytes may be seen just inside 

 the zona. In Fig. 10 the chromatin is arranged around the 

 periphery of the vesicle and not clumped to one side as in Fig. 9. 

 One notices quite a similarity between these vesicles and those 

 in process of formation in Fig. 6, and suggests that they may 

 have been preceeded by such a stage. 



After the formation of these numerous nuclear vesicles, the 

 fragmentation of the cytoplasm takes place. Figs. 16 and 17, 

 adjacent sections of a seventy-two hour egg, indicate that the 

 fragmentation may take the form of a protoplasmic budding. 

 The large cell shown in the figure has constricted off two frag- 

 ments and is forming others. Adjoining sections show five 

 additional fragments, making seven in all. Nuclear material is 

 present in only two of the seven fragments. Of course one can- 

 not say that all such fragments are constricted off from the egg, 

 for there is always the possibility that some of them may have 

 come from the polar bodies. It has been shown by Hartman 

 ('16) in the opossum, and by Newman for the armadillo that 

 normally one of the first activities of the unfertilized egg is the 

 unburdening itself of the deutoplasmic material. This is done 

 without assistance of any spindle or apparent nuclear influence. 

 While it cannot be said that the fragments budded off in the 

 mouse are exclusively of yolk material, the process is essentially 

 a similar one. 



Figs. 13, 14 and 15 are later stages in the fragmentation pro- 

 cess. They represent what Kingery ('13) calls the "morula" 

 stage. Figs. '14 and 15 represent two adjoining sections of the 

 same "morula," which consists of about twenty-one cytoplasmic 

 fragments. 



We have seen how the second maturation spindle breaks down 

 and forms either a single resting nucleus or numerous nuclei, 

 and have traced the latter to the "morula" stage. When, on 

 the breaking down of the spindle the egg is able to form a single 

 or only a few resting nuclei, it would seem to indicate exceptional 



