SPERMATOGENESIS OF LEPISMA DOMESTICA 391 



and breadth of ten representative cells of each kind, and the 

 average diameter of each cell and of the ten cells taken. 



In the second place, the chromatic nucleolus is distinctly 

 double (fig. 47), while in the spermatid it is single and smaller 

 (figs. 64, 66, and 68). 



During the growth and division period, spindle remains stand 

 out quite clearly as one, more usually as two vesicles, formed 

 probably from the central fibers and showing a granular con- 

 densation in their interior (figs. 25 and 46). 



The formation of the resting stage and the subsequent prophase 

 is a rapid one, as I have observed resting nuclei, prophase, and 

 dividing second spermatocytes in the same cyst. Figures 50 

 and 51, resting and prophase stages, respectively, are from a 

 slide not particularly well fixed, as the cells are somewhat swollen, 

 but figure 51 is interesting in that it shows the formation of 

 spindle fibers before the nuclear wall has broken down and in 

 figure 50 the idiochromosomes still show their double structure. 

 The resting nucleus, at first granular, breaks up into faintly 

 staining irregular or fantastically shaped entities without any 

 visible unraveling stage and condense quickly into the pro- 

 chromosomes (figs. 49 and 50). 



The second maturation division 



With the formation of the spindle for the second maturation 

 division, two types of metaphase plates are seen: one (fig. 53) 

 with eighteen chromosomes and another (fig. 56) with sixteen. 

 In the latter case I have one perfect anaphase (fig. 59), in which 

 both plates can be counted and both show sixteen chromosomes. 



It appears that the idiochromosomes are now equal in size 

 and no longer show a connecting thread. In the first maturation 

 division the idiochromosomes were distinctly unequal, but each 

 tapered into a thread connecting it with the other. This thread 

 often seemed ribbon-like, granular, and taking the iron haema- 

 toxylin stain like the chromosomes. 



It seems to attain its maximum length at the metaphase of 

 the first maturation division and to shorten a great deal by the 



