388 Ralph S. Li Hie 



process in facilitating developmental changes may possibly lie 

 here. 



The membrane is readily formed by brief exposure, during or 

 after the maturation stage, to the action of sea-water containing 

 xylol or ether; and such eggs show the typical irregular form- 

 changes and cleavages; I have however not yet obtained free- 

 swimming blastulae from eggs thus treated. Treatment for one 

 or two minutes with a solution of 3 cc. /^ acetic acid in 50 cc. sea- 

 water produces perfect membranes, and I have frequently obtained 

 a small proportion of swimming larvae from eggs so treated. ^^ The 

 effect must be regarded as due to the lipolytic action of the fatty 

 acid and not as a general effect of acidity (or increased concentra- 

 tion of hydrogen ions) since mineral acids — HjSO^ and HNO3 — 

 used similarly fail to produce the least sign of a membrane. ^"^ 



The abihty of mature eggs to form membranes as a result of 

 momentary warming shows a certain periodical variation, as will be 

 shown in more detail later (cf. pp. 400, 403). In general the disso- 

 lution of the germinal vesicle is an important condition, although 

 immature eggs may form perfectly typical membranes under certain 

 conditions (p. 407) . Again, as already shown, membrane-formation 

 by heating becomes more difficult after maturation is complete. 

 On the other hand, treatment with a fatty acid appears to produce 

 membranes with equal readiness at any time after maturation has 

 begun. Thus I have subjected successive portions of a single lot 

 of eggs to the action of the above acetic acid solution at 10 minute 

 intervals throughout the entire course of maturation (until the 

 separation of the second polar body) and again an hour later, 

 without finding any decided difference in effect at the different 

 periods; a small proportion of blastulae was obtained in every one 

 of the ten experiments of the series except the first (treated 10 

 minutes after removal from animal). The largest proportion of 

 larvae was obtained from eggs treated previously to the separation 



15 Compare Loeb: loc. cit., and Dynamics of Living Matter, 1906, p. 172 



i^Loeb (loc. cit., cf. also Dynamics of Living Matter, p. 170) found the same difference between 

 fatty and mineral acids. Lefevre, however, finds that in Thalassema mineral acids produce membranes 

 with the same readiness as do fatty acids. Here apparently some other action than the directly lipolytic 

 is involved. Cf. Lefevre: Journal of Experimental Zoology, vol. iv, p. 106, 1907. 



