524 FRANK R. LILLIE 



I. INTRODUCTION 



The fifth study of this series on "The behavior of the sper- 

 matozoa of Nereis and Arbacia with special reference to egg 

 extractives" forms the prelude to the present study. In that 

 paper I dealt with the phenomena of activation and of aggre- 

 gation (chemotaxis) of spermatozoa and with their agglutination 

 by egg secretions of the same species. Regarding fertilization 

 as involving chemical interaction of the ovum and " the sper- 

 matozoon, I concluded from some of the modes, of behavior of 

 the spermatozoa, especially the agglutination phenomena, that 

 "these small motile cells may prove better indicators of some of 

 the reactions involved in fertilization than the slowly reacting 

 egg" and that we might "confidently expect that study of the 

 reactions of spermatozoa will break a new path into the field of 

 fertilization." 



The results described in the present paper have been obtained 

 largely by the use of sperm-suspensions as indicators, but also 

 by the study of an inhibitor of fertilization contained in the blood 

 of certain individuals of the same species. These methods reveal 

 a striking series of facts which appear to me to justify a somewhat 

 new point of view in regard to some of the problems of fertili- 

 zation. I have already briefly presented this point of view in a 

 rather special form with an outline of the main facts in a pre- 

 liminary paper (Lillie '13). • 



The essential conclusion is that fertilization is a reaction be- 

 tween three bodies of which one is born by the sperm and one by 

 the egg; the third body, which is secreted by the egg, reacts with 

 both the others. The spermatozoon functions essentially as an 

 activator of the third body which I propose to name 'fertilizin;'' 

 the latter when activated • enters into certain reactions in the 

 cortex of the egg which lead to membrane formation. In order 

 to give a concrete working conception I have pictured the fertili- 

 zin as possessing two side chains active in fertilization, viz : one 



1 This is the same substance which I called the 'sperm isoagglutinin' in the pre- 

 ceding paper of this series, because it causes agglutination in sperm suspensions 

 of the same species. 



