STUDIES OF FERTILIZATION. 21 



significant, not the adhesion of spermatozoa to one another that 

 results in sufficiently concentrated sperm suspensions. 



One cannot therefore argue from the absence of the agglutina- 

 tion reaction in any given case that there is no connection between 

 the modification of the spermatozoon evidenced by agglutination 

 and fertilization. This is admittedly a serious limitation of the 

 method for analysis of fertilization, but the limitation does not 

 weaken the force of the positive results. 



My previous interpretation of the phenomena of fertilization 

 was that the substance that agglutinates the spermatozoa is the 

 same as that which activates the egg. I therefore named this 

 substance fertilizin, for its presence is essential for fertilization. 

 The fertilization reaction was thus conceived to be a combination 

 of a sperm component ("sperm receptors") with the fertilizin 

 of the egg, and a consequent activation of the fertilizin which 

 then reacts with egg components ("egg receptors") initiating 

 the developmental processes. 



This conception furnishes a schema within which the complex 

 events and immediate consequences of fertilization can be readily 

 comprised. The original arguments (Lillie, 1914) for the neces- 

 sity of fertilizin in the fertilization reaction were as follows : 

 (i) The production of fertilizin by eggs ceases at fertilization; 

 correspondingly the eggs are "immune" to spermatozoa. (2) 

 The production of fertilizin by eggs ceases after membrane 

 formation by butyric acid; correspondingly these eggs are not 

 fertilizable. (3) If the fertilizin content of eggs be reduced by 

 repeated washings the fertilization capacity decreases correspond- 

 ingly. (4) The production of fertilizin by eggs of the sea-urchin 

 does not begin until after maturation; correspondingly the fully 

 grown ovocytes with intact germinal vesicle are immune to 

 spermatozoa, or, if spermatozoa enter such eggs, they are entirely 

 without effect. 



These results have been confirmed and extended by Just 

 (1919) and by Moore (1916, 1917). The latter author made a 

 special study of the butyric acid reaction with special reference 

 to the question of superposition of fertilization ; while Just has 

 dealt with all of these points, especially in the case of Echin- 



