THE BIOLOGY OF THE CELL SURFACE 



2.5 gram molecular NaCl. From this solution, beginning 

 thirty minutes after immersion, thev were transferred to 

 normal sea-water at intervals of either two and one-half 

 or live minutes. This double treatment of fatty acid and 

 hypertonic sea-water results in a development that closely 

 approximates the normal, because the eggs not only show 

 separated membranes, but the larvae swim at the surface 

 of the sea-water. It is to be especially emphasized that in 

 this method the order in which the means are used is of no 

 consequence to the results obtained: the butyric acid may 

 be used before or after the hypertonic sea-water. 



For the eggs of Arbacia at Woods Hole, the method is 

 somewhat different. According to Loeb, 2 cc. of ^^f normal 

 butyric acid in 50 cc. of sea-water acting from one and one- 

 half to three minutes must be employed. Even so, Loeb 

 did not succeed in inducing the eggs of Arbacia to separate 

 their vitelline membranes; they only showed what he called 

 a fine gelatinous layer which was not easily visible. It 

 remained for Heilbrunn^ to show that the butyric acid 

 treatment for this egg must be shortened; then the vitelline 

 membranes are separated in much the same form as from 

 fertilized eggs. This I have confirmed for the eggs of 

 Arbacia. Also, I have obtained with butyric acid perfect 

 membrane-separation in the tg<g of another echinid, 

 Echinarachnius."^ 



Of this resume, although it is by no means complete, we 

 can make the following summarized statement which holds 

 for all cases of parthenogenesis experimentally induced in 

 marine eggs. 



1. Only when they are in their normal fertilizable period 

 do eggs respond to experimental means. 



2. For all eggs, one means only — as heat, cold, acids, 

 hypotonic sea-water, hypertonic sea-water, etc, — is suffi- 



^ Heilbrunn., 191 5- 

 2 Jusi, 1919c, 1920. 



222 



