STUDIES IN ARTIFICIAL PARTHENOGENESIS. 33! 



this power, before they could make their measurements. In 

 the Cumingia egg electrical measurements would be easier inas- 

 much as the normal cortical change is not membrane elevation. 



But the following point should be noted. In any measure- 

 ments of the electrical resistance of masses of egg cells, it is rather 

 doubtful if one is measuring the resistance of the cells at all. If 

 one conceives of a piled-up mass of spheres resting in a liquid, 

 it is obvious after a moment's consideration that the liquid is 

 broadly continuous from one side of the mass to the other. Thus 

 water flows readily through a pile of shot. If now the spheres 

 are poor conductors as compared to the liquid, and an electric 

 current is sent through the mass, it will flow almost exclusively 

 through the liquid. The resistance then depends on the size 

 and shape of the interspaces between the spheres. In the case of 

 egg cells this may vary in several ways. In the sea-urchin egg 

 it is certain that after fertilization the interspaces between 

 individual eggs in a mass are greater than those before fertiliza- 

 tion, for it has been shown (cf. Heilbrunn, '15) that after fertiliza- 

 tion the eggs offer much more resistance to compression and 

 hence tend to preserve their spherical shape. Thus after fertiliza- 

 tion one might expect the resistance of a mass of eggs to be lower 

 even though the electric current did not pass through the eggs 

 at all. 



In the last few years R. S. Lillie ('16, '17) has shown that when 

 fertilized or activated eggs are placed in hypotonic solutions, 

 water enters them more rapidly than it does unfertilized eggs. 

 Similarly in hypertonic solutions (R. S. Lillie, '18) water leaves 

 the fertilized eggs more readily. This is due according to Lillie 

 to an increased permeability of the plasma membrane to water. 

 Lillie's reasoning is a bit difficult to follow. Originally he be- 

 lieved in an increased permeability of the membrane to salts 

 and dissolved substances. This would of course decrease the 

 speed of entrance of water from hypotonic solutions, or the speed 

 of exit to hypertonic solutions, for it would decrease the osmotic 

 pressure upon which the exit or entrance of the water depends. 

 Osmotic pressure is, as everyone knows, dependent upon the 

 impermeability of a membrane to dissolved substances. Increase 

 in permeability to salts would therefore produce the opposite 



