THE SPERMATOGENES1S OF THE MYRIAPODS. 199 



established in the higher animals and hence it is to be expected 

 that when the karyosphere breaks down, the resulting fragments 

 should be distinct chromosomes. In protozoa the conditions are 

 different. The chromosomes are not such definite structures and 

 hence when the karyosphere of Actinospharium disintegrates it 

 gives rise to a large number of granules which later collect into 

 chromosome-like masses. However, the relationship is certainly 

 sufficiently close to warrant our placing in the same general cate- 

 gory ; the solid chromatin nuclei of some Sporozoa and Rhizopoda, 

 the karyosomes of higher protozoan nuclei, and the karyosomes 

 and karyospheres, 1 found in the nuclei of metazoan cells. 



" Chromatin nucleoli " being of such universal occurrence in 

 protozoan cells, it is to be expected that some metazoan cells ex- 

 hibit the same structure. As I have already shown, such ex- 

 amples are fairly common in germ cells and seem to be espe- 

 cially numerous in somatic cells and in the female germinal 

 elements. So far as I know they occur only in cells which are 

 undergoing especially long periods of mitotic inactivity. Such is 

 certainly very evidently true of the germ cells of Scolopcudra 

 licros where, during the time of their presence, the pseudo-ger- 

 minal vesicle stage, the cell increases many times in size. 



The pseudo-germinal vesicle stage is succeeded by the active 

 prophase of the first maturation division. This phase is inau- 

 gurated by modifications in the cytoplasm of the cell and by the 

 migration of the centrosome to the nuclear membrane. Upon 

 reaching this structure the centrosome divides and the two parts 

 begin their divergent courses. 



By the time this is well begun the nucleus also commences to 

 show signs of activity. The linin reticulum becomes more ragged 

 and the threads are now composed of finer granules. But the most 

 important phenomena are those to be observed in connection 

 with the karyosphere. At a casual glance this structure seems 

 to have undergone no change, but upon careful examination it is 

 found that its outline is now more irregular and its consistency 



1 In the above terminology I have limited the term karyosome to structures other 

 than chromosomes found within the nucleus which are apparently composed exclusively 

 of chromatin. The karyosphere is much more highly organized, as it contains chro- 

 matin (in a granular, reticular or spireme form), karyoplasm, i. e., linin and karyo- 

 lymph. It is in fact a miniature nucleus. 



