blackman: the spermatogenesis of scolopendra. 11 



rounded by a membraue much more sharply marked than that enclosing 

 the cell itself. It contains within it a large nucleolus-like body (karyo- 

 sphere) and a fine dense network of faintly staining fibres. The whole cell 

 stains very feebly with haematoxylin and the other stains employed, the 

 nuclear network being no more conspicuous in this respect than the cyto- 

 plasm. The karyosphere, however, stains very deeply, and thus shows, 

 even at this early stage, its chromatic nature, although it takes the 

 stain less readily than in the spermatocytes. When decolorizing is 

 continued long enough, it is plainly seen that this element is not homo- 

 geneous, but is very finely reticulated. It is also evident that it gives 

 up its stain much more readily than is the case in the spermatocyte, 

 which shows, I believe, that there is more linin and less chromatin 

 present in this body in the spermatogonium than in the spermatocyte. 



I have never observed a centrosome at this stage, but as the number 

 of cells studied is comparatively small, it may have been overlooked. 

 Indeed, when the fact is mentioned that from the early prophase of the 

 ensuing division up to the maturing of the spermatozoon, centrosomes 

 can be readily identified, it seems probable that they are present also 

 in the spermatogonia even at a time when these cells are not actively 

 dividing. In the succeeding prophase (Fig. 3) the cell undergoes the 

 following changes : The cell outline becomes more rounded and the 

 cytoplasm appears more transparent. Tliere are now plainly to be seen 

 in the vicinity of the nucleus two small but very distinct centrosomes. 

 These at first seem to lie free in the cytoplasm and are not surrounded 

 by a sphere nor by radiations. Later very faint radiations appear, thus 

 indicating the nature of these granules. The nucleus has also changed 

 considerably (Fig. 3) and has assumed a more nearly spherical outline. 

 The karyosphere has disappeared, and the chromatin derived from it has 

 taken the form of thirty-three small chromosomes. All of these, with 

 the exception of one, are irregular in outline and of a granular appear- 

 ance. This one, the accessory chromosome, possesses a clear-cut outline 

 and is apparently homogeneous in structure. From the phenomena 

 observed in the spermatocyte later, it is probable that in the preceding 

 resting stage this element formed the centre about which the rest of the 

 chromotin of the cell was aggregated to form the karyosphere described 

 above. 



In succeeding stages the centrosomes separate and move to opposite 

 poles of the nucleus, the nuclear membrane disappears, and the mitotic 

 figure is formed as usual. In the metaphase (Fig. 4 ; Plate 8, Fig. 125) 

 the chromosomes become irregularly arranged in the equatorial plane and 



