specificity in Fertilization 87 



acid. This membrane is so tough in the egg of Stron- 

 gylocentrotus that no spermatozoon can get through 

 it; in the egg of Arhacia the membrane is occasionally 

 replaced by a soft gelatinous film. If no second treat- 

 ment is given to such eggs they will disintegrate in a 

 comparatively short time, but when sperm is added 

 some or most of the eggs will develop in the way charac- 

 teristic of fertilized eggs. ^ When the membrane is too 

 tough to allow the spermatozoon to enter the egg it 

 can be shown that if the membrane is torn mechanically 

 the egg can still be fertilized by sperm. 



Should it be possible that the spermatozoon can no 

 longer agglutinate with the fertilized egg or that those 

 phagocytotic reactions which we suppose to play a 

 role in the entrance of the spermatozoon into the egg 

 are no longer possible after a spermatozoon has entered? 

 The mere fact of development is apparently not the 

 cause which bars a spermatozoon from entering an 

 egg already fertilized by sperm. 



Lillie assumes that the egg loses its *'fertilizin" in 

 the process of membrane formation since the sea water 

 containing such eggs no longer gives the agglutinin 

 reaction with sperm, and he believes that the lack of 

 "fertilizin" in the fertilized egg or in the egg after 

 membrane formation is the cause of the block in the 

 fertilized egg. But we have seen that the artificial 



^ Loeb, J., Science, 1913, xxxviil., 749; Arch. f. Entwcklngsmech.y 

 1914, xxxviii., 277; Wasteneys, H., Jour, Biol. Clum., 1916, xxiv., 281. 



