344 



In studying different regions of the sex-gland anläge of the 

 specimen from which Fig. 3 was taken (7.5 mm. total length), sections 

 were found in which the process had not gone so far, while in others 

 it had been carried to the point where the sex-cells were entirely- 

 separated from the body of the endoderm, Fig. 4. These differences 

 were not peculiar to any part of the sex-gland region. 



M.P. 



Fig. 3. Detail of a portion of the section shown in Fig. 2. 



This process by which the mesentery takes its origin and at the 

 same time separates the sex-cells from the main mass of the endo- 

 derm, must be a very rapid one, since it is found occurring in a re- 

 latively small proportion of embryos of 7.5 mm. length. In seven 

 specimens of this length studied, only two were in the stage shown 

 in Figs. 2 and 3, while in the remainder of them this process had 

 either just taken place or was just about to take place. 



