CELL-ORGANS OF SEA-URCHIN EGG 577 



stituted in small, intensely staining granules. Such accumula- 

 tions of achromatic granules are numerous in figures 4, 11, 13, 

 20 and 22. The nuclei of these eggs contain numerous chroma- 

 tin granules. Connections between the granules lying outside of 

 the nucleus and the chromatin of the nucleus itself can be seen 

 in figure 4. These connections are effected by numerous threads 

 of basophilic substance, partly forming a loose net within the 

 nucleus. 



The close relations between the chromatin of the nucleus and 

 the basophilic substance in the cytoplasm can be easily traced. 

 The nucleus on figure 10 offers also an example of these close 

 connections. Its membrane has almost completely disappeared 

 and a part of the cytoplasm, surrounding the nucleus, appears 

 strongly condensed and basophilic. On the side of the cyto- 

 plasm this condensation is directly connected with the network 

 of the cytoplasm, on the other side it joins directly the large 

 nucleolus. Figure 11 represents the same conditions in no less 

 characteristic way. There appear in two different places around 

 the nucleus linear condensations of cytoplasm intensely impreg- 

 nated with basophilic substance. Numerous cytoplasmic threads 

 unite these condensations with the rest of the cytoplasm as well 

 as with the chromatin particles lying within the nucleus. How 

 different these condensations may appear is shown by the figures 

 10, 11 and 12. 



Did the study of the differentiation of chromatin in the nucleus 

 of parthenogenetic eggs contribute some information about its 

 origin? At the beginning of parthenogenetic development the 

 nucleus is deprived of differentiated visible chromatin. The 

 basophilic chromatic substance, accumulated in the cytoplasm, 

 seems to be gradually transported to the region of the nucleus. 

 At the same time the nuclear membrane begins to disappear and 

 the limits between the nucleus and the cytoplasm are finally 

 effected merely by the difference of the two substances. The 

 first chromatic particles in the nucleus appear in closest relation 

 to the cytoplasm, and at first they appear as small, deeply stained 

 spots at the membrane itself. These spots grow gradually and 

 become convex toward the center of the nucleus. The nucleus 



