BLACKMAX : THE SPERMATOGENESIS OF SCOLOPEXDRA. 75 



At the stage when the lateral centrosomes enter the nucleus (Figs. 

 95, 96), there remains closely apposed to the nucleus a small hemi- 

 spherical mass of archoplasm. This persists and retains its form for a 

 considerable time (Fig. 98), hut by the time the elongation of the 

 nucleus has become pronounced, this archoplasm has been converted 

 into a number of distinct fibres, which in general extend parallel to the 

 axial filament (Fig. 100). "When these first arise they are quite distinct 

 threads irregularly disposed in the region immediately posterior to the 

 nucleus and stained by the Congo red. Soon, however, they collect 

 toward the periphery and apparently become attached to the nuclear 

 membrane, forming in longitudinal sections a line continuous with the 

 lateral outline of the nucleus and extending backward a distauce equal 

 to half the length of the nucleus (Figs. 102-104). The fibres are now 

 coarser, due to the fusing of several into one, and stain a reddish gray. 

 This fusion continues as the diameter of the nucleus becomes less, until, 

 as shown in Figures 105, 106, and 109, the fibres have all united to form 

 the cuff-shaped structure already described. The region enclosed by 

 this often stains much less deeply than the rest of the cytoplasm (Figs. 

 104, 105, 109). This is, I believe, due to the aggregation of the fibres 

 at the periphery of the region in the manner described. The cytoplasm 

 does not immediately fill the space thus left, and therefore it is occupied 

 by the more transparent hyaloplasm only. 



We have seen that, at the conclusion of the fusing of the small ves- 

 icles to form the acrosome, this is a large irregular pyriform or club- 

 shaped vesicle often exceeding the nucleus in bulk (Figs. 102-104). 

 The distal end is usually more or less enlarged, so that the irregular 

 pear shape is the more common. In the earlier stages of its formation 

 (Figs. 99-103) its proximal constricted end is in contact with the 

 nuclear membrane. Occasionally, possibly by the action of the fixing 

 reagent, the membrane, which is quite prominent, is ruptured and the 

 vesicle collapses as shown in Figure 100. 



Shortly after the acrosome vesicle has assumed its characteristic 

 shape (Fig. 103), a second much smaller vesicle appears at its basal end 

 where it comes in contact with the apex of the nucleus (Fig. 104). 

 This for a time becomes larger and larger (Figs. 105, 106, 109), and 

 then gradually diminishes in size (Figs. 110, 111), until in the mature 

 spermatozoon no evidence of such a structure remains (Fig. 121). 



When the chromatin in the nucleus again begins to regain its accus- 

 tomed affinity for stains (Figs. 104, 105), the acrosome also undergoes 

 a change by which its staining reaction is altered. Its volume is very 



