496 PROCEEDINGS OF THE AMERICAN ACADEMY. 



karyosphere possessing the regular outline has also changed in its 

 reaction to the stains, showing that it is in this part that the nucleo- 

 lar substance lies. Here certain rounded areas, which represent the 

 chromosomes, still retain the haematoxylin strongly, while surrounding 

 these chromosomes are irregular areas which show little or no affinity 

 for the chromatin stains. Thus the rounding off of the karyosphere is 

 due to the filling of the interstices between the chromosomes with 

 nucleolar material, which thus acts as the matrix in which the chro- 

 matin is embedded. The acquisition of achromatic material continues 

 during succeeding stages until, in the vesicle stage, the fully formed 

 karyosphere is considerably larger, possesses a clearly cut outline, and 

 is spherical in shape. 



The origin of the karyosphere in Lithobius multidentatus and 

 Lithobius sp. 1 differs from that in Lithobius mordax in several re- 

 spects, and at this stage the cells resemble those of Scolopendra sub- 

 spinipes more than they do those of Scolopendra heros. This is due 

 to the facts that the young spermatocytes of these two species of 

 Lithobius contain one or more true nucleoli and that this nucleolar 

 material also enters into the formation of the karyosphere. In Figure 4 

 is represented a young spermatocyte of Lithobius sp. 1 showing an early 

 stage in the formation of the karyosphere. The spermatocytes of this 

 species are characterized by the presence of two or more nucleoli dur- 

 ing the growth period. Figure 4 shows a cell possessing two nucleoli. 

 Chromatin in the form of diffuse segments is already being deposited 

 upon the surface of one of these, and the accessory chromosome may 

 be seen embedded in one side of it. The other nucleolus (Figure 4) is 

 still free of chromatin, but would later be involved in these changes 

 also. Each nucleolus usually forms the basis for a separate karyo- 

 sphere, as may be seen by referring to Figures 14, 16, 17. In Figure 

 15 one of the nucleoli contains no chromatin deposits whatever. This, 

 however, is exceptional. 



In Lithobius multidentatus the origin of the karyosphere is similar 

 to that just described for Lithobius sp 1, except that here only one nu- 

 cleolus occurs, and only one karyosphere is formed (Figures 11-13). 



After all of the chromosomes of the cell have become massed to- 

 gether to form the karyosphere, the remaining portion of the nucleus 

 no longer stains deeply with chromatin stains (Figures 5, 6) and is no 

 more dense in its structure than the cytoplasm. Soon irregular amor- 

 phous deposits appear in the nucleus, and these form a mantle sur- 

 rounding the karyosphere. This mantle, however, does not envelope 

 the karyosphere closely, but is separated from it by an area of trans- 

 parent substance so that this body seems to lie in a vacuole of hyalo- 



