[Sensitivity of the ova of Drosophila (Drosophila melanogaster, Meig.) to the lethal action of ultraviolet rays. iv. Survival of embryos irradiated at the segmentation stage].

During the early segmentation stage, Drosophila eggs are very resistant to U.V. light. At that time their survival curve presents a plateau. This inflection of the curve cannot be explained by a restoration mechanism, nor by differential sensitivity of mitotic phases. It must be ascribed to the presence in the irradiated population of eggs that have been retained and deposited after the beginning of embryogenesis. Many reasons permit to relate the decline in resistance of the eggs to U.V. light during segmentation to the decrease in the DNA content in the cytoplasm.