EFFECTS OF X-RAYS UPON HAPLOID AND DIPLOID EMBRYOS OF HABROBRACON

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Abstract
1. Comparison of radiosensitivity of haploids and diploids of Habrobracon shows that the stage of development at which the animals are x-rayed is important in determining the relative sensitivity between these groups. When embryos are x-rayed during cleavage, haploids are more resistant than diploids; when embryos are x-rayed immediately after cleavage has been completed (blastema stage), haploids and diploids are equally radiosensitive. 2. Embryos x-rayed during cleavage or early blastema are deleteriously affected during the egg stage or not at all. Those that hatch complete post-embryonic development normally. Older embryos when x-rayed may hatch, but post-embryonic development is slowed down and many of the individuals are arrested in development as larvae. Hatchability, therefore, is not an adequate criterion of radiosensitivity for older embryos. 3. Embryos that are x-rayed during cleavage and fail to hatch are arrested in cleavage or in early blastema. The nuclei are arrested at interphase and become enlarged up to four times the diameter of untreated nuclei. 4. Since the differential radiosensitivity between haploids and diploids depends upon the stage of development at which they are irradiated, it is difficult to pose a single hypothesis that will account for these facts. It seems reasonable to consider that the relative sensitivities of the cellular materials change during development and that different mechanisms may be primarily involved at different stages.