268 GERM-CELL CYCLE IN ANIMALS 



hence the spermatozoa simply initiate development. 

 The chromosome cycle of Rhabditis nigrovenosa has 

 been studied by Boveri (1911) and Schleip (1911). 



PHYLLOXERA CAKYMCAULJS 



Stem, 



o 



O 



o 



^ o 



'^^ 



J 



CiD 



O 



o 



'O'y j^ 



Sjwmatfcytt. 



FIG. 72. Chromosome cycle in Phylloxera carycecaulis. (From Mor- 

 gan's Heredity and Sex, published by the Columbia University Press.) 



