THE PHYSIOLOGY OF FERTILIZATION 167 



tion, even if the membranes formed by the butyric 

 acid be entirely destroyed. Such eggs are therefore 

 comparable to normally fertilized eggs in respect to 

 their unfertilizable condition. Moore has shown that, 

 if they be very heavily inseminated, spermatozoa may 

 enter them, but there is absolutely no reaction between 

 sperm and egg. 



Thus in the case of Arbacia, on which these 

 experiments were performed, there is no possibility of 

 superimposing fertilization upon parthenogenesis after 

 optimum exposure to the activating agent. But if the 

 exposure to the activating agent be too short, or too 

 long, some degree of capacity for fertilization exists, 

 which is expressed in Figs, iga, b. But development 

 due to insemination after too long exposure to butyric acid 

 is never normal. It is obvious that we are dealing here 

 with a quantitative relation that would be as true for each 

 egg as for the entire culture. The individual variability 

 of the eggs is what gives the percentage results. 



If we were to assume the presence of a single activ- 

 able substance within the egg for which the sper- 

 matozoa have a certain affinity the results concerning 

 superposition of fertilization on parthenogenesis could 

 be expressed as follows: Shorter exposure to the arti- 

 ficial activating agents leaves varying amounts of the 

 activable substance unengaged for sperm action; the 

 optimum exposure leaves none free; too long action 

 leaves some unengaged, owing to secondary conditions 

 produced in the pre-activation period, which hamper 

 the development after insemination. Moore has shown 

 that there is a close approximation in the content of 

 the sperm-agglutinating substance of the eggs to this 



