92 Specificity in Fertilization 



created by the entrance of a spermatozoon into the 

 egg is also due to an inhibitory substance carried by a 

 spermatozoon into the egg; and furthermore that the 

 effect of the inhibitory substance should be the pre- 

 vention of further agglutination of the spermatozoon 

 with the egg or of the growth of the pollen tube in 

 plants? On such an assumption self -sterility would be 

 due to a lack of agglutination between the egg of a 

 nermaphrodite and a spermatozoon of the same indiv- 

 idual. The experiments on the agglutinins have shown 

 that while isoagglutinins (i. e., agglutinins for other 

 individuals of the same species) are common auto- 

 agglutinins {i. e., agglutinins for cells of the same indi- 

 vidual) rarely if ever occur. 



7. A positive chemotropism of the spermatozoa 

 toward an egg of the same species has been demon- 

 strated in a few cases, but it seems that this pheno- 

 menon is not determined by that type of substances 

 which give rise to species specificity. The famous 

 experiment of Pfeffer on the spermatozoa of ferns 

 inaugurates this line of investigation. He found that 

 such spermatozoa when moving in a straight line 

 through the water will be deviated in their course 

 if they come near an archegonium; they will then 

 turn toward it, enter it, and enter the egg. Pfeffer 

 showed that 0.01 per cent, malic acid if put into 

 a capillary tube will attract the spermatozoa of 

 ferns. 



