582 FRANK R. LILLIE 



This could readily be tested experimentally, for, in such a case, 

 the mixed sperm suspension should no longer agglutinate on 

 exposure to the fertilizin of the eggs used in the experiment. 

 If, for instance, we were to find that sperm suspensions of Arbacia 

 and Nereis were antagonistic in the sense of Godlewsky, so that 

 mixtures of the two would not fertilize Arbacia eggs, then accord- 

 ing to my hypothesis the Arbacia sperm in the inhibited mixture 

 would not agglutinate with Arbacia fertilizin. The experiment 

 yet remains to be performed. 



2. THE TWO PHASES OF FERTILIZATION 



In the second study of this series (Lilhe '11) I showed that 

 fertilization involves two phases in the case of the egg of Nereis; 

 the first phase is accomplished before the penetration of the 

 spermatozoon, and leads to changes in the cortex of the egg analo- 

 gous to membtane formation in the sea-urchins. If the spermato- 

 zoon be then prevented from entering, the egg completes the 

 maturation process only and does not segment. The cleavage 

 of the egg is casued by some action of the spermatozoon after 

 penetration. Loeb had also shown by entirely different methods 

 the existence of two similar phases in the fertilization of the ovum 

 of the sea-urchin. 



The question, therefore, arises, does the mechanism of fertili- 

 zation discussed in this paper deal only with the first, or with 

 both phases of fertilization? To this it must be answered that 

 the mechanism in question is primarily the mechanism of mem- 

 brane formation. The described results demonstrate this so 

 positively that farther discussion is superfluous on this point. 



But the question remains whether there is any relation of such 

 cortical changes to the internal phase of fertilization? Whether, 

 for instance, if the spermatozoon could enter the egg without 

 first forming the combination with the cortical fertilizin, it 

 would then be in condition to carry out the second phase of fertil- 

 ization, and cause segmentation of the egg? It has been shown, 

 as is well known, that the egg can be induced to develop apparently 

 without the cortical changes involved in membrane formation, 



