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 Arbada, since the latter can be caused to 

 develop even by a neutral hypertonic solution. We pointed 

 out already that the eggs of Arbada 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 ol diflerent 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 Arbada. 



