THE SPERMATOGENESIS OF AGALENA X.KVIA. 1 29 



polar views of their respective chromosomes all in one plane. 

 The accessory chromosomes appear thick and heavy at this stage 

 (Figs. 40 and 41). Later the ordinary chromosomes are lost to 

 view in the chromatin reticulum and give rise to the resting 

 nuclei of the spermatids. 



Transformation of the Spermatids, 



One marked characteristic of the spermatids is that complete 

 separation of sister cells is long deferred and in the early stages 

 the cell-plate and interzonal fibers are conspicuous in the cyto- 

 plasmic neck connecting the two cells (Figs. 42 and 43). Near 

 the cell periphery lies the centrosome from which an extracellu- 

 lar axial filament has grown out and this filament bears at the 

 center and at the tip a transparent vesicle which stains deeply in 

 iron-hrematoxylin. The accessory chromosomes always lie near 

 the distal pole of the nucleus with their outer ends turned to- 

 ward the centrosome, so that here again we have the cell-polarity 

 as beautifully shown as it is in the spireme stage. This ability 

 to orient the cell brings to light the fact, already referred to, 

 that sister spermatids must often undergo considerable rotation 

 when they are drawing apart. In Figs. 44 and 45 the inter- 

 zonal fibers have apparently disappeared but in all probability 

 they give rise to the idiozome as claimed by Bosenberg ('05). At 

 the center of the cytoplasmic neck connecting sister spermatids 

 there is frequently a more or less evident enlargement which is 

 of sufficiently general occurrence to deserve mention and in its 

 center one finds the persistent mid-body (Zwischenkorper) even 

 at a late stage (Figs. 46-51). This enlarged portion of the neck 

 was called by Wagner the "connecting-body." 



The nucleus now takes a form which bears a strong resem- 

 blance to the contraction phase of the growth period and were 

 it not that it is of general occurrence in beautifully fixed material, 

 it might be thought due to the harmful action of the fixing fluid. 

 The chromatin reticulum contracts toward the distal pole of the 

 nucleus into a mass which stains intensely, while the greater part 

 of the nuclear cavity is left empty or is filled with nuclear sap. 

 The accessory chromosomes lie in a distinct vesicle or at least in 

 a clear space which gives them prominence and although they 



