84 Specificity in Fertilization 



more alkaline the solution. The presence of bivalent 

 cations, especially Ca, also favours the agglutination. 



It was also found that this agglutination occurs 

 only when the spermatozoa are very motile; thus if a 

 trace of KCN is added to a mass of thick sea-urchin 

 sperm so that the spermatozoa become immotile a 

 drop of this sperm will not agglutinate when put in egg 

 sea water of the same species; while later, after the 

 HCN has evaporated, the same sperm will agglutinate 

 when put into such sea water. 



The writer suggests the following explanation of 

 the phenomenon. The egg sea water contains a sub- 

 stance which forms a precipitate with a substance on 

 the surface of the spermatozoon whereby the latter 

 becomes slightly sticky. This precipitate is slowly 

 soluble in sea water and the more rapidly the more 

 alkaline (within certain limits). Only when the 

 spermatozoa run against each other with a certain im- 

 pact will they stick together, as Lillie suggested. Lillie 

 assumes that this agglutinating substance contained 

 in egg sea water is required to bring about fertilization 

 and he therefore calls it ' ' f ertilizin. ' ' ^ But this assump- 

 tion seems to go beyond the facts inasmuch as the 

 existence of such an agglutinating substance can only 

 be proved in a few species of animals (sea urchins and 

 annelids) ; and as, moreover, sea-urchin sperm can 

 fertilize eggs which will not cause the sperm to agglu- 



^ Lillie, F. R., loc. cit. 



