Varidbility of Eggs and Sperm of Sea-Urchins. 



81 



In 7/13, males Nos. 1, 2, 3, and 4 fertilized female No. 1 and gave 

 99, 83, 98, and 99 per cent cleavage respectively. With female 3, the 

 corresponding males gave 57, 30, 50, and 46 per cent. Female No. 1 

 gave consistently high cleavage by all the males, and female No. 3 gave 

 consistently low cleavage. As in rate of membrane formation, one may 

 speak of high-cleavage eggs and low-cleavage eggs. Apparent excep- 

 tions arise when low-cleaving eggs were fertihzed by high-cleavage 

 sperm. 



Table 5. — Variation in percentage of cleavage, of eggs, and of sperm 

 from different individuals of Toxopneustes. 



'Maximimi difference. 



Since the variability in the reactions between these fresh eggs and 

 sperm is so amazingly large, one should be cautious about comparisons 

 of fertilized eggs from different individual sea-urchins, even when of 

 one and the same species; yet this error is commonly made. 



