Membrane Formation 



357 



The experiments were performed on the eggs of Toxopneutes 

 variegatus. Perfectly normal membranes may be produced on 

 returning to sea-water after the acid treatment. With Hipponoe 

 the membranes formed after treatment with acetic acid are very 

 close to the egg and almost invisible with the low power, except 

 on slightly high focus when they appear separated from the egg 

 surface by a very fine clear ring. This is not apparent in the 

 untreated eggs, and in those eggs which have not responded to 

 the treatment. 



In all experiments the usual precautions against contamination 

 with sperm were taken. About 2 cc. of sea-water, densely crowded 

 with eggs, was pipetted to lOO cc. of the acid sea-water at the 

 proper temperature. The eggs were then removed from the 

 solutions at intervals to sea-water at 29° C. (the normal summer 

 temperature of the water at Tortugas) and examined for mem- 

 brane formation. The temperatures given were readings taken 

 at the beginning and end of the experiment. Controls were 

 always kept. 



EXPERIMENT I 



June 50, 7909. Eggf taken 4.4S p.m. 

 2h cc. ^ acetic acid to 50 cc. sea-water. 



EXPERIMENT II 



July 7, igOQ. Eggs taken "J.^O a.m. 

 5 ff. ^ CHzCOOH to 50 cc. sea-water. 



TIME IN MINUTES AFTER S.I5 A.M. 



