. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. SENSITIVITY OF SPERM AND EGGS 83 sperm are much more sensitive than the eggs; in the worms such as Urechis, Nereis, and Chaetopterus the sperm is slightly if at all more sensitive than the egg, as judged by cleavage delay. Such a lack of differences in susceptibility of the gametes might be more ap- parent than real. It is possible that when there is little or no cleavage delay follow- ing fertilization of an egg with an irradiated sperm, the sperm may be serving only to activate the egg to haploid parthenogenesis. Eggs of A
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. SENSITIVITY OF SPERM AND EGGS 83 sperm are much more sensitive than the eggs; in the worms such as Urechis, Nereis, and Chaetopterus the sperm is slightly if at all more sensitive than the egg, as judged by cleavage delay. Such a lack of differences in susceptibility of the gametes might be more ap- parent than real. It is possible that when there is little or no cleavage delay follow- ing fertilization of an egg with an irradiated sperm, the sperm may be serving only to activate the egg to haploid parthenogenesis. Eggs of Arbacia and of Chaetop- terus were, therefore, fertilized with sperm treated either to a small dosage or to a medium dosage of radiations and at appropriate intervals samples were fixed in Benin's fluid and stained with iron hematoxylin. Although the preparations were k ACTION SPECTRUM FOR RETARDATION OF CLEAVAGE 100 80 \ I6" 40 20 SPERM^ A X. S EGGS D SETTING ACTION AT 2804 N \ EQUAL TO 100 \ \ \ \ \ \ \. P EGGS COMPARED TO SPERM ON AN ABSOLUTE BASIS 2400 2600 280O WAVELENGTH IN A 3000 320O FIGURE 1. Action spectra for retardation of cleavage of eggs fertilized with irradiated sperm at A and for irradiated eggs at C. At B the data for the eggs are compared on a relative basis setting the value at \ 2,804 A as 100 per cent efficient. See text below. not entirely satisfactory, evidence for pronuclear fusion was observed in both cases. No lagging or disintegrating sperm were observed in the cytoplasm of either egg. Since neither cytological nor physiological evidence suggests parthenogenesis, it seems likely that for the dosage ranges tested the delayed cleavage follows fusion of the gametic nuclei. The difference between the two types of sperm must lie in some other factor. Possible explanations will be considered in the discussion. The data in Table I show that the threshold for effects on cleavage is quite dif- ferent for eggs of different species. Thus Strongylocentrotus,
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Keywords: ., bookauthorlilliefrankrat, booksubjectbiology, booksubjectzoology
