Specificity in Fertilization 79 



mixed with the sperm of certain annelids (Chcetopterus) 

 or molluscs, and if after some time the eggs of the 

 sea urchin are added to the mixture of the two kinds 

 of sperm no egg is fertilized. If, however, the solution 

 is subsequently diluted with sea water or if the egg 

 that was in this mixture is washed in sea water, the 

 same sperm mixture in which the egg previously re- 

 mained unfertilized will now fertilize the egg. From 

 these and similar observations Herlant draws the con- 

 clusion that the block existed at the surface of the egg, 

 inasmuch as a reaction product of the two types of 

 sperm is formed after some time which alters the sur- 

 face of the egg and thereby prevents the sperm from 

 entering. This view is supported not only by all the 

 experiments but also by the observation of the writer 

 that foreign sperm or blood is able to cause a real agglu- 

 tination after some time if mixed with the sperm of a 

 sea urchin or a starfish.' We can imagine that the 

 precipitate forms a film around the egg and acts as a 

 block for the agglutination between egg and spermato- 

 zoon. The block can be removed mechanically by 

 washing. 



3. The fact has been mentioned that the most 

 motile sperm will not be able to enter into the egg if 

 certain other conditions (specificity or COH or Cca) 

 are not fulfilled. On the other hand, living but immo- 

 bile sperm cannot enter the egg under any conditions. 



* Loeb, J., Jour. Exper. Zodl., 1914, xvii., 123. 



