io6 George Lejevre 



eggs, which had been fertilized by sperm; and the larvae showed 

 an equal degree of vitality" (Loeb '06, p. 168). He did not find, 

 however, that all acids were effective in causing the membrane 

 to appear; with the exception of CO,, all the membrane forming 

 acids were monobasic, organic acids. Mineral acids and dibasic 

 or tribasic organic acids, such as oxalic or citric, were not suitable 

 for the purpose. The acids that gave the best results were the 

 lower representatives of the fatty acid groups. 



A comparison of the foregoing with my own observations will 

 show some rather striking points of difference. In the first place, 

 the acids which I found to be capable of calling forth the mem- 

 brane formation are of a more widely different character, while 

 the response to the acid treatment of the egg of Thalassema in 

 throwing off the membrane does not seem to be as narrowly 

 restricted as in the case of Strongylocentrotus. Although but few 

 acids were available for use when my experiments were made, 

 those which I employed represent a series of considerable range. 

 Unlike Loeb's experience, I found that the mineral acids, HNO3, 

 HCl, and H2SO4, were quite successful with the eggs of Thalas- 

 sema, and, as a matter of fact, some of my best results were ob- 

 tained with HCl. Among organic acids, furthermore, the mem- 

 brane forming power w^as not limited to monobasic acids, for one 

 dibasic acid, at least, oxalic acid, yielded about as good results as 

 did the monobasic acetic acid. Contrary to the conclusion to 

 which Loeb came in the case of Strongylocentrotus, in Thalassema, 

 at all events, it would seem that the acid effect is essential to 

 membrane formation. 



It should also be pointed out that the limit between the minimal 

 and maximal exposure of the eggs of Strongylocentrotus required 

 for membrane formation is narrower than in Thalassema, Al- 

 though the minimal exposures given by Loeb ('05, p. 122) for 

 several different solutions of acetic acid correspond quite closely 

 at the same temperature with my observations, the eggs of Thalas- 

 sema will form membranes after being subjected to stronger solu- 

 tions and for a much longer time than is true of the sea-urchin. 

 By referring to the table on p. loi, it will be seen that the opti- 

 mum treatment in my experiments would have been a decided 



