136 ON THE SPERMATOGENESIS OF THE SIKL-WORM. 



The sperm-mother-cells with large chromatin granules and 

 distinct centrosomes, described in the last part of the grow- 

 ing stage, now entirely lose their nuclear wall and the chro- 

 mosomes become arranged in an equator of the spindle form- 

 ing a " Kernplatte " of Strasburger. In this stage, I have 

 not found any nucleolus in the " Kernplatte," while Hen- 

 king observed it in a spermatocyte of Pyrrhocoris apterus. 

 Fig. 50 shows a side view of this stage. The chromosomes are 

 arranged in a single row in the equator of the spindle, and 

 not in double rows as Henking (15, 16) and vom Rath (28) ob- 

 served in genital cells of Gryllotalpa, Pyrrhocoris and Pygaera. 

 In a polar view of " Kernplatte," we can clearly distinguish 

 twenty-eight chromosomes (fig. 52) in most of the cells, although 

 some with twenty-six or twenty-seven are sometimes to be found. 

 Each of the chromosomes of the " Kernplatte," gradually pro- 

 duces a constriction in the middle of the long axis and forms a 

 dumb-bell-shaped chromosome (figs. 50', 51). This constriction 

 deepens until two chromosomes are formed. This mode of divi- 

 sion corresponds very well with the division of sperm-mother- 

 cells of Diaptomus described by I shikawa in the following words: 

 " In the process of division each dumb-bell-shaped chromosome 

 elongates and becomes divided in its middle part, so that one 

 half of the dumb-bell goes to one pole and the other half to the 

 other. The only difference from the ordinary karyokinesis con- 

 sists in the mode of division of the chromosomes, which general- 

 ly divide longitudinally and not transversely." In fig. 50' is a 

 "Kernplatte" of a cell in which the process of the transverse 

 division of the chromosomes is to be seen. This is certainly an 

 intermediate stage which is described in fig. 50 and fig. 51. After 

 the transverse division, each row of chromosomes gradually re- 

 cedes to the pole and forms a diaster stage (fig 53). This corres- 

 ponds to the first reducing division of Weismann, each daughter 

 nucleus containing also twenty-eight chromosomes as the mother- 

 cells. Consequently, in this division no reduction of the number 

 of chromosomes takes place, as Henking observed in the egg-and 

 sperm-cells of many other animals (15, 16), while it corresponds 

 very well with the first division of a sperm-mother-cell of Ascaris 

 and Gryllotalpa described by 0. Hevtwig (18) and vom Rath (28). 



After the division the chromosomes form a somewhat granular 



