blackman: the spermatogenesis of scolopendra. 73 



in fact, they are not seen again until the cell in its metamorphosis has 

 reached the stage represented in Figure 102 (Plate 7). However, the 

 centrosome at the end of the filament persists and may be seen at almost 

 every stage. 



From the appearances seen in Figure 102 and in later stages, it cannot 

 be doubted that the two lateral centrosomes, at the time of their disap- 

 pearance, enter the nucleus, which at this stage (Figs. 95, 96) is devoid 

 of a membrane, and for a time become lost to view among the masses of 

 chromatin. They are not seen again until the chemical nature of the 

 chromatin has become so altered that it no longer assumes the black color 

 (Fig. 102). At this and all succeeding stages the two lateral centrosomes 

 are seen to be contained within the nuclear membrane, and are at all 

 stages distinguishable, although for obvious reasons they are not seen in 

 all cells. 



It may perhaps be of significance that at the time the centrosomes 

 enter the nucleus (Figs. 95, 96) the chromatin is in the granular form 

 and exhibits its characteristic reaction to stains, whereas immediately 

 afterward it begins to undergo a transformation by which all of its mor- 

 phological and chemical characteristics are altered. 



The lateral centrosomes when they again become visible within the 

 nucleus (Fig. 102) are at first small, inconspicuous, deeply staining 

 bodies, which retain the position in relation to the axial filament that 

 was characteristic of them during preceding stages. Each one is now 

 indubitably connected with the central centrosome, or end knob, by 

 means of a conspicuous fibre, which follows the outline of the nuclear 

 membrane. This condition is much better shown in Figure 103, which 

 is a drawing of one of the small spermatids at a slightly later stage. 



As the nucleus continues its transformation it assumes the shape 

 shown in Figures 104 to 108. In all longitudinal sections it appears 

 dart-shaped. The contents of the nucleus at this time are beginning to 

 regain their affinity for stains, and small masses of granular chromatin 

 are again appearing (Figs. 104, 105). This change continues to become 

 more and more marked, until at the stage represented by Figure 106 

 the nucleus as a whole assumes a very deep black stain. However, in 

 all properly stained preparations, there are certain areas which are not 

 so deeply colored; these give rise to such appearances as are represented 

 in Figures 106-108. Thus, at the anterior end of the dart-shaped head 

 of the young spermatozoon there is an area of varying extent which 

 shows a paler coloration. This is because the interior part of the head 

 here remains unstained, while a thin deeply stained layer upon the out- 



