THE PROBLEM OF ACTIVATION 233 



The conception of the mechanism of fertilization 

 resulting from these considerations would thus be that 

 a substance borne by the egg (fertilizin) exerts two 

 kinds of actions, (i) an agglutinating action on the 

 spermatozoon and (2) an activating action on the egg. 

 In other words the spermatozoon is conceived, by means 

 of a substance which it bears and which enters into 

 union with the fertilizin of the egg, to release the activ- 

 ity of this substance within the egg. 



Without stopping here to consider this matter in 

 detail let us note how the conception fits the main 

 principles of fertilization. In the first place it is 

 consistent with the major thesis that the egg is an 

 independently activable system; whether the fertilizin 

 is activated by the spermatozoon or in some other 

 way should make no difference, except in a quantitative 

 sense in certain cases, in the development of the egg. 

 In the second place it explains the association of acti- 

 vation of the egg with fertilization. In the third place 

 it explains the prevention of polyspermy, because, as I 

 have shown (p. 237), all free fertilizin is bound in some 

 way at the moment of fertilization; fertilized eggs pro- 

 duce no more of it. The method of binding we shall 

 consider later. In the fourth place it explains why 

 spermatozoa are inert in immature eggs, for these eggs 

 have not yet produced any fertilizin, as I have shown. 

 It is also entirely consistent with the facts of merogonic 

 fertilization as, determined by Delage and Wilson 

 (p. 162). Finally, it furnishes a basis for understanding 

 the problem of specificity, because the agglutination 

 phenomenon exhibits considerable specificity as we 

 have seen, and it is in certain respects analogous to 



