Improvep Metuop oF ARTIFICIAL PARTHENOGENESIS 67 
products. It turned out that the latter was the case, and that 
any monobasic fatty acid, formic, acetic, propionic, butyric, 
valerianic, etc., induced membrane formation. 
If the unfertilized eggs of S. purpuratus are placed in 50 ¢.c. 
of sea-water+2.8c¢.c. N/10 butyric acid at 15° C. and left in 
this solution for one and one-half to two and one-half minutes, 
all the eggs form membranes when replaced in normal sea-water. 
If they are transferred earlier from the acid to normal sea- 
water, they form no membrane; nor do the eggs form a mem- 
brane after remaining too long in the acid, because the acid 
injures the eggs. 
The lower monobasic fatty acids, formic, acetic, propylic, 
valerianic, and capronic acids, behave like butyric acid, 1.e., 
when these acids are added to sea-water the eggs do not form 
membranes while they are in the acidulated sea-water, but only 
after they are transferred to normal sea-water. If, however, 
the higher monobasic fatty acids are used, e.g., heptylic, capry- 
lic, nonylic, and caprinic acids, the eggs form a fertilization 
membrane while they are in the sea-water containing the acid. 
Carbonic acid behaves like the higher fatty acids. The differ- 
ent behavior of these acids finds its explanation in the fact that 
a high concentration of hydrogen ions in the surrounding solu- 
tion inhibits the membrane formation. We shall come back to 
this point later on. 
Hence if one of these lower monobasic fatty acids or car- 
bonic acid penetrates into the egg, it acts like ethyl acetate in 
producing membrane formation. If now the unfertilized eggs 
of Strongylocentrotus were first placed for two hours in hyper- 
tonic sea-water and then treated with a monobasic fatty acid, 
i.e., put for one and one-half to two and one-half minutes at 
15° CG» into. 50 c.c.. of sea-water+2.8c.c. N/10 butyric acid, 
so that all formed membranes upon transference to normal / 
sea-water, all the eggs, or the majority of them, developed 
into larvae; while, as I have said, less than 1 per cent of the 
