199 



elements is explained by Ancel by supposing the 

 transformation of the cells into sex cells to cease 



FIG. 58. Helix arbustorum. Stages in the differentiation of male and 

 female sex cells. A. Nucleus of germinal epithelium. B. Nucleus 

 of nurse cell. C. Nucleus of indifferent sex cell. D. Spermatogo- 

 nium of first order. E. Spermatogonium of second order. F. Grow- 

 ing oocyte. (From Buresch, 1911.) 



before nurse cells are formed; thus all the sex cells 

 would become spermatogonia. 



More recently Buresch (1911) has repeated the 



