Abstract
D. robusta collected in a woods in s.-w. Virginia during the spring and fall of 1950 showed seasonal changes in gene arrangement frequencies in several chromosomal arms. The two sexes are not equally responsible for these changes, most being significant in males but not in females. In one arm the gene arrangements show no seasonal changes but differ significantly in the two sexes. Apparently selection pressures on carriers of these arrangements are not identical in males and females.