ACTION OF THE HYPERTONIC SOLUTION 99 
highest percentage of larvae (viz., 7 c.c. of 23 m NaCl), 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 23 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.e. of sea-water-+0, 1, 2, 3, 4, etc., of 2 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 
foes: tol’ 5 C. 
This experiment described by Table VIII again demon- 
strates that the addition of less than 4.¢.c. of 2; 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 8c.c. of 25 m 
NaCl is added, the minimum length of exposure is 47 minutes, 
and the same is the case when 12 c.c. of 2 m NaCl is added.! 
Perhaps the following facts explain why it is not possible to 
save eggs from disintegrating by the addition of less than 4 ¢.c. 
of 23 m NaCl to 50 c.c. of sea-water after artificial membrane 
iJn these experiments the eggs were placed in the hypertonic solution very 
soon after membrane formation; otherwise the times would have been shorter. 
