2i8 PROBLEMS OF FERTILIZATION 



species. But it has hitherto been impossible to develop 

 autohaemolysins or autoagglutinins by injection of the 

 broken-down blood cells of the same individual. 



This statement will be sufficient for purposes of com- 

 parison. The analogy to fertilization would rest on 

 the resemblance of isoagglutination, for instance, to 

 cross-fertilization, and on the absence of autoaggluti- 

 nation to the absence of self-fertilization. But if the 

 egg produces a specific antibody to the sperm, as the 

 analogy suggests, this must be based on some substance 

 in the sperm, which acts as antigen, of different chemical 

 composition from the homologous substance of the egg. 

 Why then should not the antibody develop equally 

 well in the body of a hermaphrodite as of a. female, 

 seeing that the postulated differences of gametes must 

 hold equally well for both cases ? It is obvious that the 

 serum analogy breaks down here, and some new principle 

 must be invoked; for instance, that antigen and antibody 

 do not react with one another if developed in the same 

 body. But this merely restates the old difficulty. 



It is obvious that the principles of immunity cannot 

 apply to fertilization in any such sense. All we can 

 hope to utilize from immunity reactions is the fact of 

 the existence of chemical specificities of an equally 

 definite and specialized character. The mechanism 

 must be quite different in the two cases. 



3. Discussion. — If we gather together our discussion 

 of specificity in fertihzation it will be seen that the stage 

 in which the phenomenon of specificity most commonly 

 manifests itself, whether in the hybrid fertilization of 

 echinoderms, teleosts, and Amphibia or in the phenom- 

 ena of self-infertility of Ciona, is in the cortical reactions. 



