2/8 L. V. HEILBRUXN. 



In my 1915 paper, I pointed out that the earlier descriptions 

 of cortical change in the sea-urchin egg had failed to distinguish 

 between two types of cortical change. The normal change at 

 fertilization is a membrane elevation. Many reagents produce 

 this change, others however produce a swelling of the membrane. 

 The two types of change, although fundamentally quite different, 

 are not easy to distinguish morphologically, partly because the 

 surface of the egg is not especially favorable, for microscopic 

 observation. I therefore proposed various criteria to distinguish 

 them. Thus elevated membranes collapse in albumen solutions, 

 swollen membranes do not. Other criteria are easily established. 

 When eggs with elevated membranes are crushed, they flatten 

 and obliterate the perivitelline space. Eggs with swollen mem- 

 branes have little or no perivitelline space, and when they are 

 crushed, the thick membranes remain around them as before. 



Just tried none of these criteria. The membranes he describes 

 in his paper seemingly lack a perivitelline space, for he notes that 

 on return to sea-water from the hypertonic solution, the perivitel- 

 line space is not obliterated. If the membranes were separated 

 off as Just believes, and if there were a perivitelline space, one 

 would think that this space would be obliterated by the osmotic 

 expansion of the egg on return to ordinary sea-water. 



As soon as an opportunity was afforded, I repeated Just's 

 observations. With the concentrations he used (2024 P er cent. 

 2]/2 M NaCl in sea-water), no membrane elevation or separation 

 could be observed. In such solutions the membrane could be 

 seen slowly to expand and swell. There was no evidence at all of 

 a sudden movement of the membrane such as occurs when the 

 membrane is elevated. Tested with albumen solutions the mem- 

 branes did not collapse. When the eggs were compressed the egg 

 contents did not expand to the outer limits of the membrane. 

 The membranes produced by solutions of sodium chloride in sea- 

 water, or on return from such solutions to sea-water, were 

 certainly swollen and not elevated. In the light of this evidence 

 it appears that the argument advanced by Just is not valid. // 

 still remains true that all substances which produce typical mem- 

 brane elevation do in every instance cause a lowering of surface 

 tension. 



