Specificity in Fertilization 73 



distantly related. What is the character of this speci- 

 ficity? The writer was under the impression that a 

 clue might be obtained if artificial means could be 

 found by which the egg of one species might be fertil- 

 ized with a distant species for which this egg is natu- 

 rally immune. Such an experiment would mean that 

 the lack of specificity had been compensated by the 

 artificial means. It is well known that the egg of the 

 sea urchin cannot as a rule be fertilized with the sperm 

 of a starfish in normal sea water. The writer tried 

 whether this hybridization could not be accomplished 

 provided the constitution of the sea water were changed. 

 He succeeded in causing the fertilization of a large 

 percentage of the eggs of the Calif ornian sea urchin, 

 Strongyloce7itrotus purpuratus, with the sperm of various 

 starfish {e. g., Asterias ochracea) and Holothiirians by 

 slightly raising the alkalinity of the sea water, through 

 the addition of some base (NaOH or tetraethylammo- 

 niumhydroxide or various amines), the optimum being 

 reached when 0.6 c.c. N/io NaOH is added to 50 c.c. 

 of sea water. It is a peculiar fact that this solution is 

 efficient only if both egg and sperm are together in the 

 hyperalkaline sea water. If the eggs and sperm are 

 treated separately with the hyperalkaline sea water and 

 are then brought together in normal sea water no fer- 

 tilization takes place as a rule, while with the same 

 sperm and eggs the fertilization is successful again if 

 both are mixed in the hyperalkaline solution. From 



