396 HARRY H. CHARLTON 



closely adherent to the nuclear membrane as to seem a part of 

 it, while on the other hand the other body appears slightly larger 

 (figs. 77 and 78). 



The nucleus continues to stain darker, due to the enlargement 

 of the chromatin granules, and these may become joined to 

 each other and give the appearance of short threads (fig. 75). 

 The vacuolization of the nebenkern continues at the expense of 

 the central body which becomes smaller. The walls of the pe- 

 ripheral vacuoles break down, the spaces becoming larger and 

 larger, until there is but one vacuole, which may exceed even the 

 nucleus in size, with a small heavily staining central part (figs. 

 80 and 81). 



From this period on, the axial filament is in close relation to 

 the central body of the nebenkern, which in well-fixed material 

 is now seen to be made up of a spireme-like thread. I have been 

 able to follow it throughout the greater part of its course and I 

 feel almost certain that it is a single continuous thread (fig. 80). 

 The cell now begins to lengthen somewhat and the central part 

 of the nucleus to stain heavily, the chromatin moving toward 

 the nuclear center, leaving a clear transparent border (figs. 

 78 to 83). 



Unless one is fortunate with his fixation and staining, the 

 central part of the nebenkern shows no structure, but appears 

 as a glassy elliptical body suspended in the single large vacuole 

 by means of the axial thread, but it can be seen very clearly 

 that the tail filament never enters the central body, but comes 

 to lie against it. The vacuole membrane lengthens out as it 

 increases in size, while the central thread-like structure breaks 

 up into several large and many small vesicles (figs. 81 and 82). 

 There are also mitochondria-like structures located between the 

 nebenkern and the nucleus as well as some distal to the nebenkern. 



The nebenkern membrane forms apparently the sheath of the 

 axial thread, some cytoplasm forming clumps around the distal 

 part of the thread, but the vesicles in large numbers fill the 

 spaces between the spermatozoa as they increase in length. 

 The middle-piece anlage enlarges, and by a turning of the nucleus, 

 the axial filament comes to lie against it (figs. 85, 86, 88, and 90). 



