CELL-ORGANS OF SEA-URCHIN EGG 569 



4. FIRST CHANGES IN THE CYTOPLASM OF NORMALLY FERTILIZED 

 AND PARTHENOGENETIC EGGS 



The first changes in the structure of the egg after normal 

 fertihzation and artificial parthenogenesis are similar, both in 

 the formation of the membrane and also in the appearance of 

 deeper changes, which take place in the cytosome. As already 

 mentioned, the characteristic structures of the mature egg are: 

 a small achromatic spherical nucleus and numerous basophilic 

 accumulations in the cytoplasm. These accumulations appear 

 as peculiar spherical bodies. They may remain unchanged for 

 many hours in mature unfertilized eggs. The oxidation rate in 

 the unfertilized egg being low, the morphological structures 

 remain stable. 



With the penetration of the spermatozoon into the egg the 

 distribution of the basophilic substance in the cytoplasm under- 

 goes conspicuous changes. The larger accumulations invariably 

 become smaller and the basophilic substance is soon much more 

 uniformly distributed in the cytoplasm. These conditions seem 

 to be of importance, because they occur with equal invariability 

 in both the normally fertilized and the parthenogenetic eggs 

 (fig. 3 and figs. 4, 5, and 6) . In both cases the stable equilibrium 

 of the different parts in the cell seems to be disturbed and latent 

 potentialities become apparent. 



Loeb finds in fertilization and egg development an acceleration 

 of oxidation processes, and believes the synthesis of the nuclear 

 substance to be effected at the expense of the cytoplasm. He 

 admits, that the nuclear substance becomes catalysor in the 

 process of chromatin synthesis. The conception of synthesis of 

 chromatin at the expense of cytoplasm, first clearly expressed 

 by Loeb, is of great importance in the development of living 

 matter. 



The specific stimulus of the latent potentialities of the egg cell 

 is the spermatozoon, and all its constituent parts have been in turn 

 regarded as of exclusive significance in fertilization. The discovery 

 of artificial parthenogenesis by Delage and Loeb have shown 

 that, in reality, no part of the spermatozoon has such exclusive 



