ACTION OF THE SPERMATOZOON UPON THE EGG 227 



contact with the surface of the protoplasm before entering 

 varies in different cases. If the time is long enough the mem- 

 brane-forming substance may be given off to the egg and the 

 membrane formed, before the spermatozoon has entered com- 

 pletely. The formation of the membrane throws the sperma- 

 tozoon out of the egg and prevents its entrance permanently, 

 since no spermatozoon can penetrate the fertilization mem- 

 brane. Such eggs behave as if they had only undergone mem- 

 brane formation by butyric acid. They begin to develop but 

 soon perish. If, however, the spermatozoon penetrates through 

 the surface of the protoplasm before the membrane-forming 

 substance has had time to act the egg can develop. In this 

 case, in addition to the membrane-forming substance, the 

 corrective substance has penetrated into the egg. 



This idea was supported by the following observation. 

 Eggs of a purpuratus were treated with living Asterias sperm in 

 hyperalkaline sea-water, and all formed membranes. Some of 

 the eggs were left in normal sea-water as a control ; the majority, 

 however, were placed after an hour in hypertonic sea-water 

 (50 c.c. sea-water +8 c.c. 2J m NaCl) and at different intervals 

 transferred to normal sea-water. Of the control eggs, about a 

 third developed into larvae, while the remaining two-thirds 

 behaved like eggs treated only with butyric acid; they began 

 to develop and then disintegrated. On the other hand, the 

 eggs which had been exposed for about 30 to 40 minutes to 

 hypertonic sea-water all developed into normal larvae. Dead 

 Asterias sperm was absolutely ineffective. This proves, it 

 seems to me, in the most striking manner that the spermatozoon 

 also induces the development of the egg through two agencies, 

 viz., a membrane-forming substance, a "lysin" and a second 

 agent, which has the same effect as the hypertonic salt solution 

 in our method of artificial parthenogenesis. It is only when 

 both factors contained in the spermatozoon get into the egg 

 that the sea-urchin egg develops into a larva. I am unable to 



