82 ROBERT H. BOWEN. 



PLATE I. 



Fig. 10 is from Eiischistus euschist aides ; the others are from Brochymena 

 qnadripustulata. All the figures are from cells of the large generations. 



FIG. i. Early spermatid with first indications of nebenkern differentiation. 

 (Benda.) 



FIG. -2. Slightly later stage than the preceding, showing development of the 

 peripheral, chromophobic zone. (Benda.) 



FIG. 3. Peripheral, chromophobic zone completed and early differentiation 

 of the chromophilic plate-work. (Benda.) 



FIGS. 4, 5, 6. Intermediate stage in the development of the chromophilic 

 plate-work. Fig. 4 is a surface view of a small slice of the nebenkern plate- 

 work. Fig. 6 is a cross-section of the nebenkern at right angles to the major 

 axis of the spermatid, the axial filament appearing below in cross-section. 

 (Benda.) 



FIGS. 7, 8, 9. Early stage in the final condensation of the chromophilic 

 plate-work and the first appearance of the vacuoles (central substance) in the 

 chromophobic material. Fig. 9 is a cross-section of the nebenkern made like 

 Fig. 6, the tail filament appearing below. (Benda.) 



FIG. 10. Early stage in the running together of the vacuoles in the chromo- 

 phobic material to form beaded threads. (Cajal.) 



FIGS, ii, 12. Slightly later stage than the preceding, showing intermediate 

 stage in the final condensation of the chromophilic material. Fig. 12 is a 

 cross-section of the nebenkern made like Figs. 6 and 9. The beaded threads 

 are seen in the chromophobic material. (Benda.) 



FIGS. 13, 14. Later stages in the disappearance of the chromophilic plate- 

 work. Fig. 14 is at right angles to the plane of Fig. 13. (Benda.) 



