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. 



J Area of dishes same as above. 



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



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



l Used 1 drop of sperm suspension. 6 Used 3 drops of sperm suspension. 



'Used 6 drops of sperm suspension. 8 Shaken gently and frequently. 



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



10 Same removed 30 minutes after fertilization. M Same removed 45 minutes after fertilization. 



