No. 581] ENTRANCE OF THE SPERMATOZOON 273 



latter and not the former. Even if we intensify the 

 activity of the spermatozoon of Asterias by putting it in 

 hyperalkaline sea water it will not enter the egg of 



If we mix eggs of franciscanus and purpuratus in sea 

 water and add the sperm of purpuratus the eggs of 

 purpuratus will be fertilized more quickly than the eggs 

 of franciscanus; and the reverse is true if the sperm of 

 franciscanus is added to a mixture of both eggs in sea 

 water. The writer is not quite certain that this differ- 

 ence is accompanied by a corresponding difference in the 

 influence of these eggs upon the motility of their sperma- 

 tozoa. It is certain, however, that the addition of egg 

 sea water from Asterias does not help the fertilization of 

 purpuratus eggs by Asterias sperm, although the egg sea 

 water from Asterias increases the activity of Asterias 

 sperm. 



The writer is, however, of the opinion that this activat- 

 ing effect of the egg upon the spermatozoon is of the 

 greatest importance for fertilization in nature and that 

 the degree of specificity which exists (although it is far 

 from absolute) is a means of preventing hybridization. 

 The writer is under the impression that the eggs which 

 are naturally fertilized in water are fertilized almost 

 instantly after they are shed. Thus it is stated at 

 hatcheries that the egg of the salmon loses its power of 

 being fertilized in a few minutes and in the case of 

 Fvnchdus the egg loses this power also very rapidly. 

 The ripe egg of starfish dies rapidly if not fertilized. On 

 the other hand, the writer has often been struck with the 

 fact that the sperm of most marine forms when put into 

 sea water is at first practically not motile. When the 

 eggs have a specific gravity considerably greater than 

 the water (as is the case for Fundulus) the eggs will sink 

 very rapidly while the sperm remains suspended for 

 some time. Now we have mentioned that if the abso- 

 lutely inactive sperm of Asterias or Asterina comes in 

 contact with eggs of its own species (even if they are 

 immature) it is at once aroused into violent activity. If 



