26O FRANZ SCHRADER. 



Such chromosome counts were generally made in cells of the de- 

 veloping nervous tissue where division phases are common (Figs. 

 3 and 4). 



Spermatogonial divisions seem to be completed with compara- 

 tive speed, for specimens which show them are not plentiful. 

 Just as in the somatic cells the number here is undoubtedly ten 



(Fig. 5). 



The stage following the spermatogonia seems to be much longer 

 in duration. The cells increase perceptibly in size during this 

 time. The earliest phase observable shows some flocculent masses 

 of lightly staining chromatin irregularly distributed through the 

 nucleus. At one point, always at the periphery of the nucleus, 

 there is a more deeply staining mass. Nothing concerning the 

 structure of this can be made out and its shape is variable (Fig. 

 8). With progressive development this deeply staining mass 

 undergoes a few, very definite, changes. In successive steps it 

 appears that a number of more or less irregular lumps is evolved. 

 Still massed at first, these gradually become separated and then 

 it is certain that they are five in number (Figs. 8 to n). It is at 

 this latter stage that a split is occasionally visible in some of them, 

 but with increasing condensation this again becomes obliterated. 

 Throughout this development these five bodies retain a definite 

 tendency to remain in close proximity to each other, and this 

 tendency is one that persists also through subsequent stages. 



In the meanwhile the flocculent and more lightly staining chro- 

 matin has also undergone development. Before the denser mass 

 has become evolved into five distinct bodies, this chromatin has 

 been transformed into a fine network of threads. Apparently 

 these are polarized toward the dense mass (Fig. 9). Like the 

 leptotene threads of other forms, these threads shorten and 

 thicken, a process accompanied by a progressive increase of their 

 staining intensity. Polarization is finally lost, and already at this 

 stage it becomes apparent that the number of shortened threads 

 is less than ten (Fig. 10). As the threads continue their process 

 of shortening, they are counted with greater ease, and in such a 

 stage as shown in Fig. 1 1 it becomes certain that they are five in 

 number. Like the denser bodies, these sometimes show a lon- 

 gitudinal split. 



