INFLUENCE OF HYDROGEN ION CONCENTRATION. 317 



posures a still smaller proportion of them show signs of activation. 

 A 3O-minute exposure will produce polar body formation but only 

 a few eggs will fragment. A lo-minute exposure is insufficient to 

 activate at any H-ion concentration; attention is called to this 

 point because this exposure produces changes in the egg which 

 prevent fertilization by sperm. 



There is also a slow activation in alkaline sea water, beginning 

 about pH 9.6 and increasing to 10.2. The activation is apparently 

 not so intense as at pH 5.8 since an exposure of 4 to 5 hours is 

 required to induce segmentation. 



It should be emphasized that the H-ion activation of Chcetop- 

 tcnis eggs is not strictly comparable to the activation of echino- 

 derm eggs by the fatty acids. Loeb showed that in Arbacia the 

 strong acids were practically incapable of activating; the fatty 

 acids are efficient by virtue of their penetrating power. Loeb 

 obtained slight activation of Asterias eggs by treatment with sea 

 water acidified with HC1 (7), but we have obtained no activation 

 of either Asterias or Arbacia eggs by CCX-free sea water as acid 

 as pH 4.5. It is probable that the activation obtained by Loeb 

 was due to free CCX, which Delage has shown to be an excellent 

 activating agent (12). 



If Chtztoperus eggs which have been exposed to the pH solutions 

 for 10 minutes are returned to sea water and inseminated, those 

 from solutions in the neighborhood of pH 5.8 will not fertilize ; 

 they remain inert when the eggs taken from the solutions at pH 

 4.6 or 7.6 have fertilized and have undergone two or 3 normal 

 cleavages. A lo-minute exposure to these solutions, though in- 

 sufficient to activate, apparently produces some block to fertiliza- 

 tion which is not produced by equal exposures to pH 4.6 or 7.6, 

 or to the alkaline solutions which also activate. (The solid line 

 in Fig. 3 shows the proportion of eggs which fertilized in sea 

 water after an exposure of 10 minutes to the pH solutions.) But 

 if the eggs are left in the pH solutions for 30 minutes or longer 

 before being transferred to sea water and inseminated, they slowly 

 recover their fertilizability, in as much as the addition of sperm 

 causes them to segment normally to the 16- or 32-cell stage, and to 

 develop into swimming larvae of more or less normal appearance. 

 The longer the exposure to the pH solutions, the greater the pro- 



