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 
eges were transferred immediately (.e., two minutes) after 
membrane formation in 50 ¢.c. of sea-water+2 e.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 asingle 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 
