THE SPERMATOGEXESIS OF A DAPHXID. 137 



The principal stages in the spermatocytic development of 

 Simocephalus are indicated in Fig. 3. A resting spermato- 

 gonium is shown in Fig. 3, a. The spermatogonial chromosomes 

 appear to be slender more or less U-shaped rods. During 

 metaphase (Fig. 3, b), they are too closely massed to be counted. 

 I have no doubt, however, that they are considerably more than 

 eight in number. Nuclei in synizesis (Fig. 3, c} show a decided 



FIG. 3. 



contraction of the chromatin threads. No growth occurs during 

 this stage and no nucleolus is discernible. Intheprophase of the 

 primary spermatocyte (Fig. 3, d), eight distinctly double rod-like 

 chromosomes are evident. The chromosomes in this stage are 

 very distinct being more or less regularly distributed just under 

 the nuclear membrane and in over fifty cases counted the double 

 chromosomes were constantly eight in number. 



