Variability of Eggs and Sperm of Sea-Urchins. 



83 



HIPPONOE. 



The variation in cleavage of Hipponoe eggs was essentially the same 

 as in Toxopneustes. The data are brought together in table 6. 



Samples of eggs of a given female fertilized by different males gave 

 45 and 76 per cent cleavage, respectively, a range of 31 per cent. 

 (Experiment 6/21.) 



Eggs of different females fertilized by the same male varied from 5 to 

 81 per cent in the 13 experiments cited in table 6. The maximal 

 difference in each experiment was 5, 9, 10, 17, 24, 47, 54 per cent and as 

 large as 70, 74, 75, and even 81 and 83 per cent. 



In these experiments so called "good," "poor," and "bad" eggs 

 were used. These terms will later be defined in definite chemico- 

 physical entities. 



TABLE 7. Variation in cleavage of eggs and sperm of different Arbacia individuals. 



ARBACIA. 



A few observations were made upon Arbacia, which live in much 

 deeper and colder waters. The results are shown hi table 7. 



In experiment 8/2, table 7, eggs of different females fertilized by the 

 one male gave 100 per cent cleavage for each. In experiment 7/28 

 all 8 females gave a high cleavage; the maximum difference was 15 per 

 cent at end of 1 hour and only 7 per cent at end of 2 hours. In the 

 other experiments the range of variability was much greater 12, 15, 

 26, 68, 75, and 90 per cent in different experiments. There were low- 

 cleaving females (see experiments 8/12 and 8/13) ; others were sterile or 

 practically so (see 8/12 and 8/13) ; others high-cleaving females. The 

 eggs appeared alike, yet upon actual test they showed a very marked 

 range of variability. On some days all the females seemed to be high- 

 cleaving females, as in 7/28; on other days there was marked variation, 

 as in 8/12, 8/13, etc. 



