THE RELATIONS OF MAN 



The egg, or ' Ovum,' is originally formed within a 

 gland, from "which, in due season, it becomes detached, 



FIG. 13. A. Egg of the Dog, with the vitclline membrane burst, so as to 

 give exit to the yelk, the germinal vesicle (a), and its included 

 spot (6). 



B. C. D. E. F. Successive changes of the yelk indicated in the 

 text. After Bischoff. 



and passes into the living chamber fitted for its protection 

 and maintenance during the protracted process of gesta- 

 tion. Here, when subjected to the required conditions, 

 this minute and apparently insignificant particle of living 

 matter, becomes animated by a new and mysterious ac- 

 tivity. The germinal vesicle and spot cease to be dis- 

 cernible (their precise fate being one of the yet unsolved 

 problems of embryology), but the yelk becomes circumfer- 

 entially indented, as if an invisible knife had been drawn 

 round it, and thus appears divided into two hemispheres 

 (Fig. 13, C). 



By the repetition of this process in various planes, 



