CELL-ORGANS OF SEA-URCHIN EGG 571 



transported. The impregnation of the cytoplasm seems to pro- 

 ceed only to a certain degree. In the case of excessive impreg- 

 nation it becomes reconstituted in morphologically visible 

 basophilic particles. 



The basophilic chromatic substance, distributed now more or 

 less uniformly in the cytoplasm, shows definite relations to the 

 achromatic nucleus. A radial arrangement of the cytoplasm 

 now becomes evident (fig. 3) around the segmentation nucleus. 

 This radial arrangement seems to be caused by the movement 

 of the basophilic substance from the cytoplasm to the nucleus, 

 and is very conspicuous in the normally fertilized eggs as 

 well as in regularly developed parthenogenetic eggs. Accu- 

 mulations of diffuse basophilic substance may appear around 

 the nucleus as seen in figure 3. Less regular is the accumulation 

 in figures 4 and 6. Well pronounced circum-nuclear zones of 

 basophilic substance appear however infrequently in normally 

 fertilized eggs. Figures 14, 15 and 19, represent nuclei of nor- 

 mally fertilized eggs with adjacent cytoplasmic zones and show 

 only slight accumulations of basophilic substance around the 

 nuclei. 



The process of dissolution may concern all the basophilic 

 accumulations at the same time. Again, other eggs exhibit this 

 process only in the immediate vicinity of the nucleus. As result 

 in the latter case, a zone of cytoplasm around the nucleus be- 

 comes freed of all discrete masses of this substance. At the 

 periphery of such eggs many small reconstituted granules may 

 be observed (fig. 3). A characteristic feature of the small 

 granules is their location at the intersection of cytoplasmic 

 reticulum. 



The described process of diffusion and subsequent movement 

 of the basophilic substance to the nucleus occurs in a very dif- 

 ferent manner in parthenogenetic eggs. The chemical stimula- 

 lation of the egg may incite in the beginning of development 

 chemical changes similar to those observed in normally ferti- 

 lized eggs, but artificial irritation is incomparably rougher, (at 

 least by Delage's method). If the chemism of the development 

 is in principle similar in normal fertilization and in partheno- 



