CHROMOSOMES AND MITOCHONDRIA 271. 
somes (shown in black in Fig. 74), two large sex- 
chromosomes (dotted), and two small sex-chromo- 
Spermato- 
gonium. Oogonium. 
Spermato- 
cyte 1. Ordn. Oocyte 1. Ordn. 
Spermato- 
cyte 2. Ordn. 
Reifes Hi. 
Fie. 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 
