ACTIVATION OF EGGS OF SEA URCHIN. 



into NaCl + CaCl 2 or into NaCl + KC1 + CaCl 2 had formed 

 a better and apparently stronger membrane than those put into 

 NaCl + KC1. 



In another experiment it was found that in a mixture of NaCl 

 + MgCl2 in the proportions in which these two salts occur in 

 the sea-water a membrane formation was also possible, but the 

 membrane had the same fine and thin character. In all these 

 cases the eggs could be fertilized with sperm in spite of the mem- 

 branes. The writer is under the impression that no second mem- 

 brane was formed upon the addition of sperm and only the hya- 

 line membrane developed later. That the eggs after this 

 inefficient membrane formation were not in the same condition 

 as eggs which are put into normal sea-water after artificial mem- 

 brane formation was shown by the fact that when put into a 

 hypertonic solution for from thirty to sixty minutes not a single 

 egg could be induced to segment. 



The fact that the membrane always collapsed after some 

 time seems to indicate that it soon became permeable for the 

 colloids liquefied at the surface of the egg in the process of mem- 

 brane formation. 



5. The explanation of the phenomenon of ineffective mem- 

 brane formation will probably be the same as that for the cases 

 of reversible activation of the egg. It is an established fact 

 that the rate of oxidations in the egg of purpuratus is raised about 

 600 per cent, by the act of fertilization. This rise is entirely 

 due to the alteration of the surface layer of the egg which results 

 in the membrane formation since artificial membrane formation 

 alone has the same effect on oxidation. Even if the egg is 

 killed in the process of membrane formation, e. g., if we treat the 

 unfertilized egg with saponin and leave it in this solution, the 

 rate of oxidation is raised to the same amount. 1 The amount 

 to which the artificial membrane formation raises the rate of 

 oxidations in a sea-urchin egg seems to be a constant for each 

 species and not to depend upon the nature of the agencies em- 

 ployed for this purpose. 



When we treat the unfertilized eggs of purpuratus with a hy- 

 pertonic solution (without inducing a membrane formation) the 



1 Loeb and Wasteneys, Jour. Biol. Chem., XIV., 479, 1913- 



