Osmotic PARTHENOGENESIS 61 
hypertonic solution possesses a rather high concentration of HO 
ions. This is more important for the eggs of S. purpuratus 
than for those of Arbacia, since the latter can be caused to 
develop even by a neutral hypertonic solution. We pointed 
out already that the eggs of Arbacia require for their develop- 
ment a lower concentration of hydroxylions than the eggs of 
purpuratus. I published the sugar experiment in order to 
leave no doubt that the hypertonic solution produces its effect 
only in virtue of its capacity for withdrawing water, and that 
we are not dealing with a specific action of salts or their ions.! 
This series of investigations established still another point of 
theoretical importance. The egg loses water in the hyper- 
tonic solution; but when replaced into normal sea-water it 
naturally takes up water again. The question now arose 
whether the causation of development depended in this case 
upon the withdrawal of water, or whether the swelling of the 
egg, when it was replaced in normal sea-water, had something 
to do with the result. With this object in view, unfertilized 
sea-urchin eggs were placed for a long time in slightly hyper- 
tonic sea-water, viz., 93 c.c. of sea-water+7 c.c. 2 m NaCl 
solution. Now it turned out that some eggs began to segment 
in that solution and that a few reached an early blastula stage 
and swam about. That they developed no farther is due to the 
fact that even so weak a hypertonic solution harmed the eggs 
when they remained in it too long. Hence the experiment 
showed that, so far as the developmental effect of the hyper- 
tonic solution is concerned, it is unnecessary to replace the 
eggs in normal sea-water. The latter is only necessary if we 
wish to maintain the eggs in their complete vitality and to allow 
them to develop into plutei. 
At that time I was inclined to assume that the effect of 
the hypertonic solution consisted in the liquefaction of the 
1 The eggs of different females show a different degree of sensitiveness to the 
treatment with hypertonic sea-water. The eggs of S. purpuratus are more often 
refractory than those of Arbacia. 
