Abstract
1. Radiation of the unfertilized eggs of Chœtopterus results in injurious effects which do not become manifest until after the extrusion of the polar bodies, following insemination with normal sperm. That two normal mitotic divisions should intervene after radiation and only then that the injury to the chromosomes becomes apparent can be explained by the fact that the two longitudinal divisions preparatory to polar-body formation have been completed. Only when the chromosomes again "grow" in preparation for a new division do abnormal characters manifest themselves. 2. If the radiation is brief (20 to 30 min.) the germ nuclei fuse normally but the radiated egg chromatin fails to form normal chromosomes. No spindle fibers develop from these abnormal chromatin masses, and they remain in the cleavage plane during mitosis. If the radiation is longer (35 to 50 min.) the chromosomes, after the extrusion of the polar bodies, develop abnormally and fail to fuse with the sperm nucleus. In both cases the sperm nucleus divides and development is androgenetic. 3. During cleavage the most injured chromatin does not move and lacks spindle fibers. This suggests that the fibers are normally developed under the influence of the chromosomes and that the latter are concerned in their own movement.
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