234 E - G - SPAULDING. 



opment in Asterias. These two seemingly contradictory effects 

 cannot, however, be so in reality and the difficulty may be done 

 away with if it is borne in mind that the effect depends as much 

 on the character (electronic) of the colloid as on the agent. For 

 on positively charged particles the H ion would have a repelling, 

 /. c., dissolving ; on negatively charged, the opposite effect. 



If all the protoplasm of the Arbacia egg was uniformly posi- 

 tive just prior to or during segmentation it accordingly might be 

 deduced that H ions would have the same effect in increasing the 

 osmotic pressure as does ether, and so of inhibiting development. 

 Lillie, 1 however, has shown that at cleavage the cytoplasm is 

 markedly electropositive, the nucleus negative. Accordingly at 

 that time he holds that the periphery repels the free kations 

 within the egg and the nucleus the anions, so that the kations 

 then predominate at the center, the anions at the periphery. As 

 like charges repel each other, this is made to account for the con- 

 stricted form of the egg at cleavage. In agreement with this 

 view the effectiveness of the H ions, in parthenogenetic methods, 

 in the environment might be considered to be due to their induc- 

 tion of a predominance of negative charges at the surface and 

 this in turn of positive charges at the astral centers. If this be 

 so, however, then other kations ought to have the same effect ; 

 but they do not. This indicates a specific action by the H ion, 

 which it might have in accordance with its high diffusion velocity. 

 It alone might therefore be considered to penetrate the egg mem- 

 brane because of its and the latter's definite chemical make-up ; 

 yet there remain difficulties even here in explaining why it should 

 do this, since, if, at least before cleavage, the membrane and cyto- 

 plasm are themselves positive they would tend to repel the H 

 ions rather than to attract them. Only provided the surface were 

 negative from the start could the attraction be explained. If, 

 however, the egg, when jus f about to divide, were put into such 

 a medium of H ions, it is reasonable to suppose that since the 

 surface at least then is negative these might be attracted ; but 

 again it is difficult to understand how they can go further, since 

 the cytoplasm is even yet positive. However, if they succeed 



1 Lillie, R. S., Am. Jour, of Physiology^ VIII., IV., and BIOI OGICAL BULLETIN, 

 IV., 4. 



