Abstract
(1) It has been proved by this experiment that there exists a regionally differential susceptibility to X rays in the first chromosome of Drosophila virilis.
(2) X-raying causes a decrease in the amount of crossing-over in the distal region and an increase in the proximal region; the middle region remains unaffected.
(3) The effect of X-raying seems to appear first on the sixth day, and attains the climax between the seventh and ninth day and disappears between the sixteenth and eighteenth day.
