THE PROBLEM OF ACTIVATION 245 



connotation for a process that occurs in normal ferti- 

 lization. 



Loeb also postulates a similar mechanism for ferti- 

 lization. To make the parallelism between fertilization 

 and parthenogenesis complete, Loeb emphasizes the fact 

 that the sperm may cause membrane formation with- 

 out entering the egg, but that, as in the case of artificial 

 membrane formation alone, development goes no far- 

 ther. Thus fertilization exhibits two phases which 

 Loeb compares to the cytolytic action and the correct- 

 ive action in his method of artificial parthenogenesis. 

 It is true that any genetic process admits of division, 

 and we have seen in discussing partial fertilization that 

 the action of the spermatozoon may be stopped, not 

 only at the moment of penetration, but at any time 

 thereafter. Such a parallelism between parthenogenesis 

 and fertilization would hold for any theory of activation. 



Loeb also holds that the spermatozoon carries a 

 substance (lysin) into the egg which effects an altera- 

 tion of its surface layer, apparently of the nature of a 

 cytolysis (1916, p. no). If this were so, it would follow 

 that two or more spermatozoa would increase the corti- 

 cal changes above the normal, but this is not the case; 

 from which it follows that the cortical changes result 

 from action of the egg itself. With reference to the 

 cortical changes, as with reference to the later phases 

 of fertilization, the spermatozoon is merely an activator, 

 and this is why under optimum conditions the egg does 

 not respond more energetically to an excess of sperm 

 than to a single one. 



Attempts to isolate a cytolytic substance from sper- 

 matozoa have signally failed, as we have seen (p. 133), 



