No. 581] ENTRANCE OF THE SPERMATOZOON 271 



action of eggs of the same and various foreign species 

 upon spermatozoa. Since the spermatozoa of the sea 

 urchins are usually very active in pure sea water (i. e., 

 sea water free from egg substance) it was necessary to 

 find a solution in which these spermatozoa will keep alive 

 for a number of days without showing any motility. 

 Such a solution was found in a neutral m/2 XaCl solution 

 and this led to the method of putting ovaries and testes 

 directly into such solutions instead of into sea water. 1 * 

 The ovaries and testes were first washed repeatedly in 

 these solutions to free them from the blood or its salts, 

 and then one drop of eggs and one or more drops of the 

 sperm suspension were mixed in a watch glass containing 

 5 c.c. m/2 NaCl (free from egg contents). In one experi- 

 ment the sperm and eggs of two sea urchins, purpuratus 

 and franciscanus, and two starfish, Asterias ochracea 

 and Asterina (at Pacific Grove), were used. None of 

 the four forms of spermatozoa showed any motility in a 

 pure NaCl solution (without egg contents). In sea 

 water (free from egg contents) the spermatozoa of the 

 two forms of sea urchins were very active, those of the 

 starfish were immobile. The starfish eggs were imma- 

 ture and did not mature during the experiment (those of 

 Asterias were out of season and very small) ; the sea 

 urchin eggs were mature. The result is indicated in the 

 following table. 



That there exists no strict specificity is obvious by the 

 fact that the immature eggs of Asterina activate the 



