SPERMATOGENESIS OF LEPISMA DOMESTICA 397 



The body then flattens out against the nucleus and later elon- 

 gates slightly (figs. 85 and 90). The nucleus lengthens, and as 

 it does, the axial filament between the middlepiece and the 

 centrosome does likewise. The centrosome, however, is now at 

 the apex of the nucleus and will hereafter be considered ~as the 

 acrosome. 



At the time when the nebenkern membrane and its vesicles 

 have completely broken up and are only apparent as end products 

 ensheathing the elongated tails or located between the filaments, 

 the nucleus is still spherical, compact, and does not take the 

 haematoxylin stain very well (fig. 82). It still has a clear area 

 about it and some mitochondrial material about the middle- 

 piece anlage, which is a quite prominent body located usually 

 on the opposite side of the nucleus from the acrosome. The 

 axial filament arising from the acrosome at the apex of the 

 nucleus is bent backward and passes near the middle-piece 

 anlage. 



The further changes are the loss of the clear ring about the 

 nuclear chromatin by the spreading out of the chromatic material. 

 The nucleus shows better staining qualities. The axial filament 

 comes to lie nearer to the middle-piece and the latter may some- 

 times show one or more bubbles or vesicles, which are possibly 

 mitochondrial, in relation to it (figs. 84, 85, and 86). 



The nucleus now begins slowly to elongate and seems some- 

 times to pull away from the acrosome, so that part of the latter 

 body may project beyond the nucleus. The nucleus continues 

 to lengthen, the chromatin to appear paler in color. The mid- 

 dle-piece enlarges and elongates (figs. 88, 89, 90, and 91). The 

 axial filament strand between the acrosome and the middle-piece 

 remains applied against the nucleus and sometimes may show 

 one or several splits in the thread, leaving an elliptical opening. 

 In material stained for mitochondria, a cloud of granules seems 

 to gather about the thread (fig. 87). Although it cannot be 

 traced directly, I am of the opinion that this axial filament, 

 which is loosely applied to the outer nuclear surface, becomes the 

 undulating membrane of the mature spermatozoon. 



