206 JACQUES LOEB 



hypertonic solution causes membrane formation. The fatty acids, 

 if properly applied, cause a typical or an atypical membrane 

 formation in practically every sea urchin egg. The hypertonic 

 sea water, however, causes an atypical membrane formation in 

 the eggs of only a small percentage of the females of purpuratus 

 and a larger though limited percentage of the eggs of Arbacia. 

 As the writer pointed out years ago, the purely osmotic method 

 of artificial parthenogenesis gives better results if the solution 

 is rendered more alkaline. 



6. In order to avoid misunderstandings it may be well to point 

 out that in the purely osmotic method of artificial parthenogenesis 

 the causation of development is also due to two factors: a mem- 

 brane-forming and a corrective factor. The peculiar fact is 

 that one and the same external agency, the hypertonic solution, 

 produces both effects simultaneously. It produces the corrective 

 effect in all cases, if the eggs are left long enough in the solution. 

 It induces membrane formation in a limited number of cases. 

 The eggs develop into larvae only if both effects are produced by 

 the hypertonic solution, otherwise the membrane formation has 

 to be induced by some other agency, for example, the addition 

 of some alkali to the solution or the treatment of the eggs after- 

 ward with a fatty acid. 



It may be that the membrane formation by the hypertonic 

 solution is always the combined effect of the HO ions and the 

 hypertonic solution, even in neutral hypertonic solutions, where 

 the CoH = 10~''N. But this conception may be unnecessary.'' 



7. We are now in a position to answer the question from which 

 we started as to which of the two factors of fertilization (the 

 membrane-forming and the corrective one) was responsible for 

 the saving of the life of the egg. The answer must be that it is 

 the combined effect of both factors. Our experiments have shown 



^ In a former paper the writer had suggested that the HO ions contained in 

 the hypertonic solution might furnish the first factor; this conclusion was reached 

 under the influence of the experiments on purpuratus where a neutral hypertonic 

 solution as a rule never induces artificial parthenogenesis. In Arbacia, however, 

 a neutral hypertonic solution docs easily induce the formation of parthenogenetic 

 larvae. 



