Variability of Eggs and Sperm of Sea-Urchins. 



79 



VARIATION IN MEMBRANE FORMATION. 



In order to determine the normal variability in the rate of fertiliza- 

 tion-membrane formation, it was important to ascertain the degree of 

 variability due to differences in different samples of sperm and that due 

 to differences in different batches of eggs. A number of the experi- 

 ments to test this point are given in table 4. 



Table 4. — Variation in rate of membrane formation in eggs from different females. 



^No membranes appeared in first 10 minutes. 



When females Nos. 1, 2, and 3 in experiment 7/1 were fertilized by 

 male No. 1, fertihzation membranes first appeared in 6, 4, and 4 

 minutes respectively. The same females tested at the same time 

 by male No. 2 produced membranes in 3| minutes in one female, 

 and none in the other two females. Male No. 3 gave the same results as 

 No. 2. In experiments 7/13 the membranes first appeared in 30 seconds 



