THE PERMEABILITY OF CELLS 549 



agent must be on the egg surlace alone and not the catalytic 

 acceleration of any reactions within the egg through an excess 

 of OH ions. 



A resistance to the entrance of NaOH is likewise shown by the 

 eggs of Holothuria Floridana, Hipponoe esculenta, Pentaceros, 

 reticulatus, and Asterias vulgaris. 



A comparison of the entrance of alkali into fertilized and un- 

 fertihzed eggs has shown that the fertilized eggs of Toxopneustes 

 are much more readily entered b}^ NaOH just after fertilization 

 and again about the time of first cleavage. Only one experiment 

 was performed toward the end of the breeding season and the 

 eggs of the female used cleaved in the control in many instances 

 somewhat irregularly. A stock solution of ^^ NaOH in 0.5 m 

 NaCl was made up. The unfertilized and fertilized eggs at 

 intervals after fertilization were compared with each other as to 

 entrance of NaOH, in separate watch glasses over a white back- 

 ground. It is thus easy to see when all the eggs have been en- 

 tered by the alkali, and their original red color changes to yellow. 

 The following table shows the result. 



The eggs begin to cleave about 45 minutes after fertilization. 



A somewhat similar result is obtained by comparing mature 

 Asterias eggs fertilized and unfertilized, as well as eggs treated 

 with acetic acid. The latter form artificial membranes. The 

 results are shown in the following experiment. 



