ACTION OF THE HYPERTONIC SOLUTION 99 



highest percentage of larvae (viz., 7 c.c. of 2J m Nad), a further 

 increase in concentration does not decrease the time during 

 which the egg has to remain in the hypertonic solution. This 

 has some bearing on the theory of the action of the hypertonic 

 solution. Since the loss of water by the egg in this solution 

 increases with its concentration, it is obvious that the effect of 

 the hypertonic solution does not grow in proportion with the 

 loss of water on the part of the egg. 



This experiment has been very often repeated with an essen- 

 tially similar result. The addition of only 3 c.c. of 2J m NaCl 

 to 50 c.c. of sea-water has never led to the development of a 

 larva of S. purpuratus after membrane formation, however 

 long the eggs are left in the solution. 



An example of such an experiment with a longer range of 

 time should be mentioned. The unfertilized eggs of a female 

 S. purpuratus were placed after artificial membrane formation in 

 50 c.c. of sea-water+0, 1, 2, 3, 4, etc., of 2J m NaCl. After 37, 

 47, 57, 110, 150, 200, 280, and 340 minutes a portion of eggs from 

 each bowl was replaced into normal sea-water. Temperature 

 16.5 to 17.5 C. 



This experiment described by Table VIII again demon- 

 strates that the addition of less than 4 c.c. of 2J m NaCl to 

 50 c.c. of sea-water is not sufficient to protect the eggs from 

 decay and evoke development even after prolonged exposure. 

 Moreover, it is clear that when once the optimum is reached 

 the time of exposure cannot be decreased by a further raising 

 of the concentration of the sea- water. When 8 c.c. of 2J m 

 NaCl is added, the minimum length of exposure is 47 minutes, 

 and the same is the case when 12 c.c. of 2J m NaCl is added. 1 



Perhaps the following facts explain why it is not possible to 

 save eggs from disintegrating by the addition of less than 4 c.c. 

 of 2J in NaCl to 50 c.c. of sea-water after artificial membrane 



1 In these experiments the eggs were placed in the hypertonic solution very 

 soon after membrane formation; otherwise the times would have been shorter. 



