324 bulletin: museum of compakative zoology. 



versing its mode of formation. At the same time, as already noted, the 

 karyoplasm becomes less dense, and soon disappears, leaving the nucleus 

 in the "empty" and transparent condition (Fig. 80). After the final 

 disintegration of the nucleolus the net continues to thicken, and the ka- 

 ryosomes appear to fuse along the course of the strands, the result of 

 these processes being the formation of a chromatin net composed of a 

 comparatively small number of more or less separate segments. In the 

 present generation this net is seldom or never so homogeneous and con- 

 tinuous as in corresponding stages in the primary spermatocytes, but 

 the majority of cells show the condition clearly seen in Figure 80, where 

 the segments are fully formed in only a portion of the nucleus, while in the 

 remainder the threads and karyosomes still remain more or less separated. 

 I am by no means certain that any further concentration of the chro- 

 matin in the net form is normally attained, nor have I been able to iiud 

 any evidence, any more than in the preceding generations, that this net 

 is ever metamorphosed into a continuous spireme thread. But, unfortu- 

 nately, the number of cells examined at this stage was rather small, so 

 that it has been less easy to trace the actual conditions than in the pre- 

 vious generation, in which they were exceedingly abundant (page 315). 

 As far as staining reactions are concerned, the cells under consideration 

 show the characters typical of prophases in general. When treated with 

 the Auerbach mixture, the nucleolus is always stained a very clear green. 

 Up to the time of the disappearance of the karyoplasm, the reticulum 

 and the karyosomes select the red (acid) dye, but after that event they 

 select the green (basic), so that their chemical reaction evidently under- 

 goes a reversal from basic to acid. 



That the chromosomes of the secondary spermatocytes always appear 

 to be formed before the bi-eaking down of the nuclear membrane, con- 

 stitutes a very striking difference between the prophase of the second 

 spermatocyte and that of other cell generations. Just prior to the dis- 

 solution of the membrane, the cells present the appearance shown in 

 Figure 81. The chromosomes are dense, oval, and still connected with 

 one another by continuous linin strands. They are present, as we might 

 expect, in the reduced number, probably twelve. The membrane now 

 breaks down, the nuclear area is filled with cytoplasm, and the chromo- 

 somes arrange themselves in the equator of the cell in a typical plate 

 (Fig. 84). In polar views of this stage, which are rather common in 

 sections, it is comparatively easy to count the chromosomes, and there 

 is, I think, no doubt that the reduced number is twelve (Figs. 82, 83). 

 The spindle is exceedingly small, the equatorial plate being not over 



