The spermatogenesis of Peripatus (Peripatopsi>) balfouri. . 315 



The form of the resting spermatocyte is always somewhat elongate, 

 varying from an ovoid to a very elongate shape (Figs. 101, 103, 104, 

 106, 108—111, Plate 20; Fig. 127, Plate 21). But the polarity which 

 became marked in the early anaphase is still retained without any 

 change: the nucleus with a small sheath of cytoplasm around it marks 

 the central pole; the distal pole is marked by the greatest amount 

 of cytoplasm and yolk aud by the idiozome body; sometimes in the 

 rest stage the Zwischenkörperchen plate still persists and aids in 

 determining the position of the distal pole. The exact form of the 

 cell body is determined by the amount of pressure exerted upon it 

 by the contiguous cells. Those spermatocytes of the rest stage, as 

 well as many of those in the early prophases of the 1st maturation 

 division which lie close to the central lumen of the testis, are often 

 much elongated, and frequently clusters or tufts of cells are found 

 with their thicker central poles (those containing the nuclei) directed 

 towards the testicular lumen, and with their distal ends pointed in 

 the opposite direction (Fig. 127, Plate 21; Fig. 247, Plate 24; Fig. 109, 

 Plate 20). Such shapes are of course directly referable to lateral 

 pressure exerted by the surrounding growing cells, this pressure 

 tending to force the cells into the central lumen ; but it is about the 

 time of the formation of the spindle in the succeeding prophase that 

 the cells appear to first become free in the lumen, so that probably 

 the formation of the spindle, in its virtue of rounding off the cell 

 mass, completes the loosening of the cells from one another. 



The cytoplasm increases considerably in amount in the rest stage. 

 It appears to have a deHcate reticular structure with rather coarse 

 meshes ; no longer is a clear vacuole found around each yolk globule. 

 The amount of yolk in the rest stage is very considerable, greater 

 perhaps than in any spermatocytes yet described except those of 

 Ascaris. The yolk globules are now smaller and stain more faintly 

 than those of the spermatogonia, and many of them appear hollow. 



VI. The Maturation Mitoses. 

 1. Prophases. 



a) Idiozome Mass and Cent rosomes. 



At the height of the rest stage the idiozome cup attains its 



deepest staining intensity. From the beginning of the prophase on 



(Figs. 129—134, 138, 160-165, Plate 21; Figs. 166-169, Plate 22) 



it gradually loses this density of stain, becoming paler and less clearly 



