INITIATION OF DEVELOPMENT IN EGG OF ARBACIA. 393 



water. With the hypertonic solutions used in the experiments 

 here presented, the case is quite otherwise : one simply notes the 

 time in hypertonic sea-water to membrane separation and allows 

 roughly twice this length of time before removal to normal sea- 

 water. 



But the main point in these experiments, it seems to me, is not 

 the inferiority or the superiority of this method of a single ex- 

 posure to hypertonic to the butyric acid-hypertonic sea-water 

 method. If the experiments here reported simply revealed that 

 the single hypertonic sea-water treatment only calls forth mem- 

 brane lifting, they would be, it seems to me, worthy of report. 

 And for this reason: If hypertonic sea-water be capable of induc- 

 ing membrane separation, then we must discard the superficial 

 cytolysis-corrective factor hypothesis for experimental partheno- 

 genesis, as we have already discarded this hypothesis as explaining 

 fertilization. I propose, therefore, to discuss these results, since 

 they involve to a far-reaching degree current conceptions of the 

 mechanism of experimental parthenogenesis. 



II. 



The evidence submitted above shows (i) that sea-water, if made 

 sufficiently hypertonic, is alone capable of inducing membrane 

 separation in the eggs of Arbacia; (2) that such eggs give good 

 cleavage and practically normal gastrulae and plutei ; and (3) that 

 the highest per cent, and normality of cleavage and of plutei result 

 when the membrane separation most closely simulates the separa- 

 tion of the vitelline membrane as a cortical response to insemina- 

 tion. If this be true, several important considerations follow with 

 regard to the nature of the processes underlying membrane separa- 

 tion and to the interpretation of these processes in the physiology 

 of the developing egg cell. These considerations follow : . 



i. In the first place, membrane separation certainly can not be 

 due to any mere surface tension change. According to Traube, 1 

 substances are effective in calling forth membrane separation the 

 more they lower surface tension. From this it follows that hypo- 

 tonic sea-water should be capable of inducing membrane separa- 



1 " Ueber Parthenogenese." J. Traube, Biochem. Zeitschr., Bd. 16, 1909, 

 pages 182-186. Cf. also, McClendon, Am. Jour. Phys., 10, 27, 240. 



