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Toxopneustes

female, eggs and cent

TOXOPNEUSTES.

The total cleavage is dependent upon the kind of male as well as the kind of female, just as we have observed in the case of the fertilization membrane. For example, 5 samples of the eggs of a given female were fertilized by 5 different males; the percentage that cleaved in 1 hour in these 5 samples was 80, 23, 35, 68, and 43, respectively, a range of 57 per cent. ( See table 5, experiment 7/3.) When different samples of eggs of a single female were fertilized by the same male the maximum difference was within 5 per cent—i. e., the experimental error was below 5 per cent.

When different females were fertilized by the same male, all suspen sions being standardized, the variation in cleavage was surprisingly large. It varied from 1 per cent in experiment 7/2B to 98 per cent in many experiments, 7/21, 7/19, 7/14, 7/12, etc. The range of varia bility as expressed by the difference between maximum and minimum cleavage for any given experiment in which a given male fertilized different females, was 11, 15, 16, 39, 48, 51, 52, 53, 54, 55, 57, 72, 74, 75, and as large as 87 per cent.

In a second series of experiments different males were used either with samples of a given female or with different females. (See experi ments 7/1, 7/13.) 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 fertilized by high-cleavage sperm.

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.