CHROMOSOMES AND MITOCHONDRIA 271 



somes (shown in black in Fig. 74), two large sex- 

 chromosomes (dotted), and two small sex-chromo- 



Spermato- 

 gonium 



Sperm ato- 

 cyte 1. Ordn. 



Sperm ato- 

 cyte 2. Ordn. 



Spermien 



Oogonium. 



Relfes Ei. 



FIG. 74. Diagrams showing the chromosome cycle in the pteropod 

 mollusk, Creseis acicula. In order to simplify the diagrams each 

 black chromosome is made to represent eight ordinary chromosomes. 

 (After Zarnik, 1911.) 



somes (dotted). The spermatogonia enter the mat- 

 uration period in this condition. The number of 



