300 T. H. Morgan 
BI eR NG eo 
Cc 
oe) 63 
eh 
vw 
l 
OP HG 
y 
oC ve 
8) ® 
) 
Yr Zz a 
~ 
Fig. XX Aphis salicola. -C, spermatogonial nuclei; D—F, stages just prior to first spermato- 
cytes; G, equatorial plate of first spermatocyte; H—X, stages in division of first spermatocytes; Y, rudi- 
mentary cells; Z,equatorial plates of second division; A’ second spermatocyte division, B’ ,after division. 
