210 GERM-CELL CYCLE IN ANIMALS 



Regarding the differentiation of the germ cells in 

 hermaphrodites then we may recognize two principal 

 views : (1) that there is some material within the 

 cell which initiates specialization, or (2) that differ- 

 entiation is due to general or local causes outside 

 of the germ cells. The former is favored by Elpatiew- 

 sky (1909, 1910) from studies on Sagitta and by 

 Demoll (1912) from studies on Helix. The second 

 view is more widely advocated. The conclusions 

 derived by Kuschakewitsch (1910) and Champy 

 (1913) on amphibians, and of Ancel (1903) and 

 Buresch (1911) on Helix agree in their essential fea- 

 tures. All of these investigators maintain that the 

 sex cells pass through an indifferent stage and are 

 differentiated into oocytes or spermatocytes because 

 of influences external to themselves. Buresch and 

 Champy also believe that even in the fully developed 

 germ glands of the adult these primitive cells are 

 present. The causes of their differentiation, how- 

 ever, have not been definitely determined. 



