COMPARATIVE SENSITIVITY OF SPERM AND EGGS TO ULTRAVIOLET RADIATIONS

¹ Marine Biological Laboratory, Woods Hole, Mass. and Hopkins Marine Station, Pacific Grove, Calif. and Stanford University, California

1. The action spectrum for the retardation of division of eggs fertilized with irradiated sperm resembles the absorption of ultraviolet light by nucleoproteins.

2. The action spectrum for retardation of division of irradiated eggs of the sea urchin resembles absorption by simple proteins like albumin except that at the short wave-length end there is no increase in action at 2,483 Å where absorption shows a definite upswing.

3. The absolute amount of energy required to affect division to the same extent by affecting the sperm is very much less than that required to affect eggs.

4. Other Echinoderms tested show a similar difference in susceptibility of eggs and sperm: S. franciscanus, Arbacia punctulata, Dendraster excentricus, and Pateria miniata.

5. Animals other than Echinoderms tested did not show as striking a difference between susceptibility of eggs and sperm: Urechis caupo, Mactra sp., Chaetopterus pergamentaceus, and Nereis limbata.

6. In the eggs listed in paragraph 5, determinations are made more difficult by the tendency for the eggs to show irregular cleavage rather than retarded cleavage as the dosage increases. Such irregular cleavage occurs in Echinoderm eggs as well but the threshold is higher.

7. If both eggs and sperm of the sea urchin are irradiated the effect on the rate of division is less than the sum of the effects which would be expected on each of the gametes alone. However, the percentage of abnormal cleavage greatly increases.

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