100 GERM-CELL CYCLE IN ANIMALS 



several others there are two methods of origin, and 

 primary and secondary sex cells are produced. The 

 former are probably derived from the blastomeres; 

 whereas the secondary sex cells are entirely inde- 

 pendent and arise from the ccelomic epithelium. 



The first statement of the theory of early segre- 

 gation was made by Nussbaum (1880), who studied 

 the history of the germ cells in the trout. Following 

 Nussbaum, Eigenmann (1892, 1896) contributed to 

 the support of the theory by his investigations on 

 the viviparous teleost, Cymatogaster. This proved 

 to be excellent material for such studies and led 

 Eigenmann to the conclusion that the germ cells 

 are set aside in this fish during the early cleavage 

 stages of the egg, probably at the thirty-two cell 

 stage. In other cases it has been impossible to 

 trace the germ cells back to such an early embryonic 

 condition, but nevertheless the evidence has been 

 almost uniformly in favor of early segregation. 

 Some of those who have advocated such an early 

 origin of germ cells are Wheeler (1900) in the lamprey, 

 Beard (1900, 1902) in Raja and Pristiurus, Nussbaum 

 (1901) in the chick, Woods (1902) in Acanthais, 

 Allen (1906, 1907, 1909, 1911) in Chrysemys, Rana, 

 Amia, and Lepidosteus, Rubaschkin (1907, 1909, 

 1910, 1912) in the chick, cat, rabbit, and guinea-pig, 

 Kuschakewitsch (1908) in Rana, Jarvis (1908) 

 in Phrynosoma, Tschaschkin (1910) in the chick, 

 von Berenberg-Gossler (1912) in the chick, Schapitz 

 (1912) in Amblystoma, Fuss (1912) in the pig and 

 man, and Swift (1914) in the chick. This is by no 



