Membrane Formation 



375 



salts, solanin and saponin to be. The specific ions may well 

 increase the permeability of egg cells, for their action on other 

 tissues is of this nature. In the alkali and alkaline earth metals 

 this has been very clearly brought out by Lillie's work on Areni- 

 cola larvae, already mentioned. 



It seems probable that the induced increase of permeability 

 brings about the development of an egg for the same reason that 

 the increase on stimulation brings about contraction in muscle 

 cells, namely, by permitting, at the proper time, the escape of 

 some reaction product which is preventing, by its accumulation, 

 the further proceeding of reactions in the egg. This is one very 

 important way in which chemical equilibria may be upset in fluid 

 mixtures surrounded by membranes whose permeability may 

 vary. The reaction product which escapes may be simply COj, 

 (as appears to be the case in muscles) or some more complex sub- 

 stance, (as the membrane substance) or both. A discussion of 

 this with practically no experimental data would be useless, 

 however. 



The facts which indicate a momentary increase in permea- 

 bility of the surface membrane, as the first change taking place 

 in the development of an egg, may be summarized as follows:^* 



1 The general similarity in the means of stimulating eggs to 

 divide, and the means of stimulating muscles and sensitive plants. 

 These may be broadly classified as chemical, mechapical, elec- 

 trical, thermal, and osmotic. 



2 The fact that the chemical substances which start partheno- 

 genesis cause in other cells an increase in permeability (haemoly- 

 sis of red blood corpuscles and loss of pigment in pigment tearing 

 cells). 



3 Evidence that stronger concentrations of development 

 starting substances cause loss of pigment in pigmented eggs. 



4 That a secretion is the first visible change occurring in many 

 eggs. 



5 That a migration of pigment-containing granules to the cell 

 surface in Arbacia eggs is caused by a region of positive change 



^ These are quoted unchanged from mv article in Science. 



