80 ARTIFICIAL PARTHENOGENESIS AND FERTILIZATION 



myself that membrane formation is the real force that activates 

 the unfertilized egg, it was necessary to show that all sea-urchin 

 eggs can be caused to develop through this agent alone. 



In my earlier experiments the eggs were placed in the potas- 

 sium cyanide sea-water very soon after membrane formation. 

 Now this is in great part answerable for the fact that the num- 

 ber of eggs which afterward developed into larvae remained so 

 small. For I have recently found that if the eggs are placed in 

 this solution a little later a large percentage of larvae can be 

 obtained and in many experiments all the eggs developed into 

 larvae after transference to normal sea-water. In this experi- 

 ment a very weak solution of KCN was used, viz., a mixture of 

 50 c.c. of sea-water +1 or 2 c.c. 1/20 of 1 per cent KCN. 



Membrane formation was produced in the eggs of a sea- 

 urchin (S. purpuratus) by means of butyric acid. Some of the 

 eggs were transferred immediately (i.e., two minutes) after 

 membrane formation in 50 c.c. of sea-water +2 c.c. 1/20 of 

 1 per cent KCN. After three, four, and five hours the eggs 

 were transferred to normal sea-water (after they had been 

 freed from KCN by thrice washing in sea-water). The tem- 

 perature was 11 . 5 C. Not a single egg developed into a larva. 



A second portion of the eggs was placed in the sea-water 

 and potassium cyanide twenty minutes after membrane forma- 

 tion. After three hours some of these eggs were transferred to 

 normal sea-water and about 5 per cent developed into larvae. 

 About 10 per cent and 20 per cent of larvae respectively were 

 produced by the eggs removed from the cyanide sea-water 

 after four and five hours. 



A third portion of the eggs was transferred to the cyanide 

 sea-water forty-three minutes after membrane formation. 

 Practically all of the eggs transferred to normal sea-water after 

 three hours developed into larvae. The eggs that remained 

 longer in the cyanide were injured and did not develop so well. 



Eggs transferred to the cyanide sea-water fifty-seven 



