104 EDMUND B. WILSON 
PLATE 1 
EXPLANATION OF FIGURES 
All the figures from photographs of sections. Enlargement 1500 diameters. 
10,11 First spermatocyte-division (N. hilaris) 
12,13 The same (N. viridula) 
14,15 Second spermatocyte-division (hilaris) 
16-25 Side views of second division (hilaris). The XY-pair shown in 16-23, the 
d-chromosome in 16, 17, 20, 24, 25; the small chromosome is evident in 
10, 12, 13, 14,15; 17, 18. 
22 ~=Initial separation of X and Y 
23 Early anaphase, X and Y separating near the center (hilaris) 
26-28 Nuclei from the growth-period, showing chromosome-nucleolus and plas- 
mosome (hilaris) 
29 Corresponding stage (viridula) 
