Explanation of Plate III. 



Fig. 27. This shows the nebenkern elongating. The axial filament passes 

 over its surface. 



Fig. 28. A little later than fig. 27. 



Fig. 29. Shows cross-sections of elongating nebenkern: a shows axial fila- 

 ment, nebenkern and acrosome: in b the axial filament is cut at an angle. 



Fig. 30. A little later than fig. 28; the axial filament not so plainly shown. 



Fig. 31. The ring has disappeared, and the dark mass is passing down along 

 the filament. The acrosome is indistinct. 



Fig. 32. The nebenkern has disappeared, but the acrosome has kept its posi- , 

 tion. 



Fig. 33. The acrosome has flattened against the nucleus. Some remains of 

 the nebenkern are seen. 



Fig. 34. The acrosome has moved to the side of the nucleus. Some neben- 

 kern remains are shown. 



Fig. 35. The acrosome is in front of the nucleus. 



Fig. 36. A little later stage than fig. 35. 



Fig. 37. Shows a divided acrosome. It is not a frequent appearance. 



Fig. 38. The nebenkern appears as a hanging drop on the side of the axial 

 filament. 



Fig. 39. The nucleus has condensed, the walls have thickened, and the chro- 

 matin appears in granules. The acrosome is pointed. 



Fig. 40. A little later stage than 39. 



Fig. 41. A little later stage than 40. 



Fig. 42. The head is stained intensely, while the acrosome is lighter. Prob- 

 ably a middle piece indicated. 



Fig. 43. The head shows the clear space. 



Fig. 44. Cross sections of the head, of the stage shown in fig. 43. 



Fig. 45. The head and part of the tail of a mature spermatozoon. 



