28 OSBORN. [Vol. XVIII. 



in a faintly stained mass which occupies most of the cell, and 

 which appears to be the nucleus. In some cases there is a 

 faint indication of a nuclear membrane nearly coinciding with 

 the cell boundary. Nothing- that I can identify as chroma- 

 tine is seen in these cells. In July the parietal cells are very dif- 

 ferent, as seen in Figs. 37 and 40, when a small amount of 

 cytoplasm can be seen, and in it a nucleus filled with deeply stain- 

 ing chromatine and a grain in the cytoplasm which has the appear- 

 ance of a centrosome. The central cells in the resting spermary are 

 much larger than the parietal. Fig. 39 is drawn from one of them 

 in the same section as Fig. 38 and with the same magnification. 

 There is a considerable amount of cytoplasm, and a nucleus of the 

 same texture, with a nuclear membrane which is only seen by 

 using the most careful illumination. In these cells deeper stained 

 grains on the edge of the nucleus are probably cromatine. These 

 cells are not apparently in groups as in the active organ. Fig. 37 

 is a camera lucida drawing of the active spermary. It shows 

 active parietal cells in a layer around the edge ; generally they are 

 in a single layer though in places they are more numerous, and the 

 center occupied by cells very different in character from those on 

 the wall, being often in groups and presenting certain nuclear 

 differences of importance. These central cells are in the act of 

 spermatogenesis, some of the phases of .which are clearly indicated. 

 In so far as I have been able to interpret the spermatogenesis 

 from my material the order of the events is indicated by the order 

 of the drawings in the plate. The parietal cells become active (40) 

 and detach themselves from the wall (41) ; the nuclear material 

 divides without the division of the cell, forming a syncytium, 

 increasing very much in size (42). This then passes toward the 

 center of the spermary and the nuclei take the position seen in Fig. 

 43 and cell boundaries begin to appear on the periphery, but the 

 mass is still one in the center, like the centro-lecithal segmentation 

 of some arthropods. At this stage, of which very many cases can 

 be found (see Fig. T^y), there are generally about six rather large 

 cells in the transverse section. Each of these cells has an abundant 

 cytoplasm, and a nucleus which is filled with chromatine in the 

 form of a fine network in contrast with the small number of dis- 

 tinct loops as sho.wn in Fig. 41. No nucleolus occurs in these cells. 



