Variability of Eggs and Sperm of Sea-Urchins. 



75 



Table 1. — Toxopneustes. Variation of membrane formation and cleavage caused by increasing the 



concentration of eggs and sperm. 



'Area of dishes same as above. 



2The per cent cleavage at 120 minutes includes only normally cleaving eggs. Hence the lower figures. 



^Used 2 drops of sperm suspension. ^Used 4 drops of sperm suspension. 



*Used 1 drop of sperm suspension. 'Used 3 drops of sperm suspension. 



'Used 6 drops of sperm suspension. ^gij^ken gently and frequently. 



•Five drops of culture removed to 10 c.c. of sea-water, 15 minutes after fertilization. 



^•Same removed 30 minutes after fertilization. "Same removed 45 minutes after fertilization. 



