SPECIFICITY IN FERTILIZATION 219 



The various methods used to induce hybrid fcrtihza- 

 tion— staHng of eggs, high concentration of sperm, use 

 of alkahes or other chemicals — have therefore this one 

 feature in common, that they destroy the chemical or 

 physical integrity of the cortex of the egg. Thus is 

 rendered possible a form of reaction common to all 

 gametes, the inclusion of the spermatozoon within the 

 egg. Specific factors then do not apparently intervene 

 until after the meeting of the germ nuclei. 



If there is indeed a specific factor in the cortical 

 reaction it can hardly be of a purely physical character, 

 though physical factors must be of significance in any 

 case; for the specific factor must include not only 

 the incompatibilities in hybrid ferlihzation but also 

 those in self-fertihzation where the physical resemblance 

 of the gametes excludes a purely physical explanation 

 of the phenomenon. We are therefore forced to the 

 conclusion that there is a chemical specificity, more or 

 less narrow, in the union of the gametes. The only 

 phenomenon in which we can so far detect a closer 

 approach to this problem is that of sperm agglutination 

 by egg secretions. 



A warning is in place here against too much reliance 

 on the phenomenon of specific agglutination in the 

 field of immunology by way of comparison. It may 

 turn out that there is a much closer relationship be- 

 tween these phenomena than we can now detect, or 

 they may represent only superficially similar phenomena 

 with the factor of specificity in common, and that onl}- 

 to a certain extent, at present unknown. 



We have the very striking fact reciprocal to speci- 

 ficity in fertilization, that spermatozoa, of certain forms 



