No. 581] ENTRANCE OF THE SPERMATOZOON 281 



in the unfertilized egg and that the egg can only be fer- 

 tilized as long as this " fertilizin " is present in the egg. 

 It is obvions that such an assumption demands for its 

 proof that in all cases in which an egg can be fertilized it 

 must contain the agglutinating substance. There is only 

 one test for the presence of this substance, namely the 

 cluster formation of the sperm in the presence of egg sea 

 water. This proof can not be furnished since, as the 

 writer had shown in a former paper, the reaction is lack- 

 ing in many cases of hybridization; it is also lacking in 

 the case of the starfish. 23 It is not impossible that if the 

 theory is tested further it will be found lacking in a con- 

 siderable number of cases. To this objection Lillie re- 

 plies that it is not necessary that the eggs should actually 

 give the agglutinin reaction, it is sufficient that the ag- 

 glutinating substance is contained in the egg. But how 

 can we tell that it is contained in an egg which fails to 

 give the agglutination reaction as long as this reaction is 

 the only reliable test for the presence of the agglutinating 

 substance in the egg! Rigorously speaking, even if all 

 eggs of every species gave the agglutinin reaction it would 

 still be necessary to furnish a direct proof that the ag- 

 glutinin has anything to do with fertilization and develop- 

 ment. 



It may be possible that Lillie considers such a proof 

 to be contained in the following statement. 



I adopted then the working hypothesis that this substance 24 is neces- 

 sary for fertilization and there followed immediately three corollaries, 

 viz.: (1) if it were possible to extract this substance from eggs they 

 would no longer be capable of fertilization; (2) fertilized eggs are inca- 

 pable of uniting nuain with spermatozoa, hence if the hypothesis is 

 correct they could no longer contain free fertilizin; (3) eggs in which 

 membranes have been formed by methods of artificial parthenogenesis 

 become incapable of fertilization; such e<j-s must also therefore be de- 

 void of free fertilizin after they have reached the non-fertilizable con- 

 dition if the hypothesis is correct. These consequences were actually 

 found to be true." 



23 Lillie, Biol Bull, XXVIII, 18, 1915. 



a *The "fertilizin." 



25 Lillie, Jour, of Exper. Zool, XVI, 523, 1914. 



