8o Specificity in Fertilization 



If we add a trace of KCN to the sperm of Arbacia so 

 that the spermatozoon becomes immobile no egg is 

 fertilized even if the eggs and the sperm are thoroughly 

 shaken together; while the same spermatozoa will 

 fertilize these eggs as soon as the HCN has evaporated 

 and they again become motile. It was formerly 

 thought that the spermatozoon had to bore itself into 

 the egg, being propelled by the movements of the 

 flagellum. It is, however, more probable that only 

 a certain energy of vibration is needed on the part of 

 the spermatozoon to make the latter stick to the surface 

 of the egg and agglutinate and that later forces of a 

 different character bring the spermatozoon into the 

 egg. The fact that under normal conditions a very 

 slight degree of motility on the part of the spermatozoon 

 allows it to enter the egg of its own species seems to 

 favour such a view. 



It is a common experience that spermatozoa become 

 very active when they reach the neighbourhood of an 

 egg. v. Dungern assumed that only foreign sperm 

 became thus active, but F. R. Lillie 1 has pointed out 

 that this may be a specific effect. The writer tested 

 this idea on the sperm and eggs of two species of star- 

 fish and of sea urchins. It should be mentioned that 

 the eggs of the starfish used in this experiment were 

 completely immature and could not be fertilized, while 

 the eggs of the sea urchins were mature. The testicles 



1 Lillie, F. R., Jour. Exper. Zool., 1914, xvi., 523. 



