No. 581] ENTRANCE OF THE SPERMATOZOON 275 



more rapidly to the bottom than the spermatozoa it is 

 also very probable that the eggs are fertilized before they 

 reach the bottom of the sea. We can understand under 

 these circumstances that the specificity which exists in 

 the activating effect of the egg upon the sperm is one of 

 the safeguards against hybridization for eggs that are 

 fertilized in the water, inasmuch as this specificity acti- 

 vates the sperm of the same species much more quickly 

 than that of a foreign species. Other safeguards are the 

 phase-boundary conditions which we discussed in the 

 previous chapter. 



V 



If we assume that the spermatozoon bores itself into 

 the egg by the energy of the vibrations of its flagellum it 

 is easy to understand the importance of its motility for 

 this process. It is, however, equally possible that a cer- 

 tain energy of vibration is needed to make the spermato- 

 zoon stick to the surface of the egg and that afterwards 

 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 sper- 

 matozoon allows it to enter the egg seems to favor such a 



von Dungern had already discussed the possible role 

 of phenomena of sperm agglutination in fertilization as a 

 protective agency. F. Li Hie discovered the transitory ag- 

 glutination of sperm induced by a substance from eggs of 

 the same species. 18 When the sperm of the sea urchin 

 Arhac'ut is mixed with the supernatant sea water from 

 eggs of the same species a cluster formation occurs which 

 may last a number of minutes and which is essentially n 

 transitory agglutination. In Arbacia the agglutination 

 is very striking, in purpwratus the phenomena of agglu- 

 tination are not lacking but the writer was under the im- 

 pression that other phenomena of the type of tropisms 



and left that question open for further discussion. 1 The 



