BLACKMAN. — SPERMATOGENESIS OF THE MYRIAPODS. 337 



tion, shows the outer layer of intensely staining chromatin and the inner 

 nucleolar material, containing several vacuoles. 



More commouly, however, the karyosphere exhibits the reticular ap- 

 pearance represented in Figures Sf, 9. Here the chromatin is very 

 plainly of the nature of a superficial spireme or a reticulum, which does 

 not completely invest the nucleolus. The appearance of the karyospheres 

 of this nature is strikingly similar to that of a small nucleus in which the 

 chromatin is spread out over the periphery of the nuclear area in flaky 

 masses (Figure 9). 



Meanwhile the accessory chromosome has undergone no apparent 

 change, and throughout the growth period has preserved the same relation 

 to the nucleolus which it had during the early spermatocyte stages (Figures 

 5-11). Occasionally an accessory chromosome is not to be seen, owing 

 to the fact, doubtless, that the section is cut in such a plane that the 

 chromosome is concealed hehind the karyosphere or does not lie in the 

 same section with it (Figures 11, 12). 



In S. subspiuipes, just as in S. heros, a number of small granular 

 masses of a deeply staining substance are scattered throughout the nucleus. 

 These stain similarly to chromatin ; inasmuch, however, as such masses 

 are also present at various places in the cytoplasm outside the nucleus, 

 it seems probable that they are not chromatin, but metaplasm — i. e., 

 that they are either food material or by-products of the cell's activity. 



In S. heros the first changes in the active prophase of the division of 

 the first spermatocyte manifest themselves in the cytoplasmic structures ; 

 they consist in the dissolution of the archoplasm and the migration of the 

 centrosomes. In S. subspinipes this is not true. Here the first marked 

 change affects the chromatin. The chromosomes do not arise as distinct 

 entities from the karyosphere by a simple disentanglement of the spireme, 

 but the chromatic portion of the karyosphere is merely detached in the 

 form of a varying number of flaky reticular masses, which thus come to lie 

 free in the nuclear vesicle. These spongy masses of chromatin do not rep- 

 resent single chromosomes, for they later break up into several smaller 

 masses, which soon take on the form characteristic of tetrads in the 

 prophase. Figure 14 represents a spermatocyte in the very early 

 prophase, in which the chromatin has just left the karyosphere. There 

 are several chromatin masses ; of these the larger one contains nearly 

 all of the chromatin. Figures 15-18 represent slightly different stages, 

 a little older than that shown in Figure 14. In Figure 15 the chromatin 

 is in several masses, of which the larger ones doubtlessly represent several 

 chromosomes. In Figures 17 and 18 the chromatin has separated into 

 vol. xli. — 22 



