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 
