234 PROBLEMS OF FERTILIZATION 



immunity agglutination, in which the specific factor is 

 very marked. 



Loeb (1914, 1915, 1916) has raised the following 

 objections to the conception: (i) That the action of 

 the egg secretions on spermatozoa is probably not a 

 true agglutination; an objection that he later with- 

 drew. (2) That the agglutinating substance is derived 

 not from the egg but from the jelly layer surrounding 

 the egg. This also is incorrect, as I have shown in a 

 separate paper (1915; cf. also Just, 1919). (3) That 

 eggs deprived of their jelly by acid produce no more 

 fertilizin and yet are capable of fertilization. I have 

 shown (Lillie, 1915) that they do produce fertilizin as 

 long as they remain fertilizable. (4) That eggs of sea 

 urchins activated by butyric acid and hence devoid of 

 fertilizin are yet fertilizable. This objection has been 

 fully discussed already (pp. 165-67). (5) That aggluti- 

 nation is sometimes absent in hybrid fertilization; thus 

 specifically " the supernatant sea- water of Strongylocen- 

 trotus franciscanus will not induce cluster formation 

 [i.e., agglutination] of the sperm of S. purpuratus; yet 

 the latter sperm fertilizes the eggs of franciscanus" 



The last objection requires some consideration. 

 Agglutination of sperm is merely an indicator of the 

 presence of a certain substance which is none the less 

 present in S. franciscanus, as proved by agglutination 

 of its own sperm, even if S. purpuratus sperm does not 

 reveal it; it may nevertheless be activated by S. pur- 

 puratus sperm, and this is all that the theory requires. 

 The phenomenon of agglutination of sperm with each 

 other is not of the least significance as such in fertiliza- 

 tion, which consists in the union of a single spermato- 



