STUDIES OF FERTILIZATION 557 



The question may be raised why such neutraUzation of the 

 fertilizin is delayed until the moment of fertilization? The 

 answer to this difficulty is fairly clear. The fertilizin is located 

 in the col'tex of the egg, and the anti-fertilizin is more 

 deeply situated ; they therefore do not interact so long as the cell 

 body as a whole is quiescent. But as soon as the cortical fertilizin 

 becomes activated by union .with the sperm it at once begins to 

 attack certain substances in the egg, as demonstrated in the 

 third part of this paper; this sets up diffusion evidenced by escape 

 of pigment, and by cytoplasmic flowing, and the two substances are 

 brought together and interact. While this explanation is partly 

 hypothetical, the spatial separation of the fertilizin and anti- 

 fertilizin and the quiescent character of the cell-body in the 

 unfertilized egg are facts; so also are the movements of diffusion 

 and the cytoplasmic currents set up on fertilization. However 

 it is possible that some other factor is operative in the inter- 

 action of fertilizin and anti-fertilizin following fertilization, which 

 has entirely escaped attention. 



c. The cessation of fertilizin production after formation of 

 membranes by butyric acid 



Some methods of artificial parthenogenesis cause eggs to be- 

 come non-fertilizable ; others apparently do not. In the sea- 

 urchins it would seem that those methods that cause membrane 

 formation result in the non-fertilizable condition while those 

 which do not, need not have such an effect. Thus the use of 

 hypertonic sea-water causes a certain amount of parthenogenesis 



this as noted. But Delage farther asserts that a second change occurs after the 

 formation of the second polar globule so that non-nucleated fragments again 

 become sterile, although entire eggs can still be fertilized. This result is un- 

 supported so far as I know, and would be diffcult to explain on the basis of the 

 mechanism described in this paper except on the assumption that the original 

 contribution of nuclear sap necessary for the production of fertilizin has become 

 exhausted, and that presence of the nucleus had become necessary for continued 

 production of fertilizin. Delage shows that during the fertilizable period of the 

 cytoplasm when merogony can be effected parthenogenetic agents are especially 

 effective, a result that agrees particularly well with my point of view. 



