346 ROBERT CHAMBERS. 



The inability of the endoplasmic sphere to develop is not due 

 to the lack of successful sperm entry. Sections show that the 

 sperm enter with ease but they remain unchanged and no asters 

 form about them. In this regard the sperm react exactly as 

 they do when they have entered immature eggs. 



There must be something localized in the cortex which is nec- 

 essary for successful fertilization and development (cf. Lillie, 

 '14, '18). On the evidence presented here we may assume that 

 this substance, originally within the germinal vesicle, diffuses 

 out upon its dissolution and accumulates in the cortex of the egg. 

 It is held in the cortex of the egg and is not carried out in, the 

 endoplasmic spheres on crushing the egg. The spheres are, 

 therefore, incapable of being fertilized. Finally, the variation 

 in the ability to segment among exovates containing varying 

 amounts of cortical material indicates that there must also be 

 a definite minimum amount of this substance present in order 

 that an egg fragment may develop. 



CONCLUSIONS. 



1. The nucleus possesses a morphologically definite membrane. 



2. Tearing the nucleus results in an immediate change of the 

 nuclear membrane, followed by a disintegration of the cytoplasm 

 surrounding it. This is most striking in the relatively large 

 nucleus (germinal vesicle) of the starfish egg. 



3. Injection of the germinal vesicle sap of one egg into the 

 cytoplasm of another egg starts up disintegration processes in the 

 injected area. 



4. The mature egg nucleus can be pinched into two fragments. 

 The fragments behave like fluid droplets and will run together 

 when contiguous. Eggs whose nuclei have been operated upon 

 in this manner are capable of normal segmentation. 



5. A membrane can be demonstrated adhering to the surface of 

 the unfertilized starfish, sea-urchin and sand-dollar eggs. This 

 egg membrane is most pronounced in the starfish and least of all 

 in the sea-urchin. In the starfish and sand-dollar the membrane 

 can be stripped off without injuring the egg. In the starfish a very 

 delicate egg membrane can be demonstrated investing half -sized 



