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 coelomic 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 Acanthats, 
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 
