206 GERM-CELL CYCLE IN ANIMALS 



and Kuschakewitsch (1910), who refer to the her- 

 maphroditic individuals as intermediates. 



There is no consensus of opinion regarding the 

 origin of the germ cells in amphibians ; one group 

 of investigators, including Allen (1907) and King 

 (1908), recognize a definite keimbahn, whereas many 

 others (Semon, 1891; Bouin, 1900; Dustin, 1907; 

 Kuschakewitsch, 1910 ; Champy, 1913) believe they 

 arise from the germinal epithelium or near-by cells. 

 Very few students have attempted to determine the 

 stages in or causes of the differentiation of male and 

 female cells from the primordial germ cells. Kuscha- 

 kewitsch (1910) concludes from his extensive studies 

 on the history of the germ cells in frogs that at first 

 all of the germ cells are indifferent but subsequently 

 become differentiated in two directions. Champy 

 (1913) has studied this differentiation in a number 

 of amphibians and has concluded that if the charac- 

 teristically lobed or polymorphic nuclei of the pri- 

 mordial germ cells in Bufo, Hyla, and Rana temporaria 

 lose their original shape and become spherical and 

 clear, the germ gland will form an ovary ; but if the 

 nuclei retain their primitive condition, a testis will 

 result. Champy believes with Kuschakewitsch that 

 both sorts of germ cells arise from sexually indifferent 

 cells, that is, sex is not irrevocably fixed in the fer- 

 tilized egg. Furthermore Champy's observations 

 have led to the conclusion that the germ cells in the 

 sexually indifferent germ glands are morphologically 

 identical with primitive spermatogonia. These in- 

 different germ cells become differentiated into ova 



