1. The factors for red and for white eye color and for normal and yellow body color in Drosophila have been the subjects of investigation in these experiments. 2. In the F2 generation the factors for eye color and body color appear to a great extent associated in the same combinations that were present in the grandparents, the interchanging taking place only once to nearly eighty cases where there is no interchanging. 3. The absence in a fly of certain characters found in the normal wild fly, seem to render it less fertile, or at least such flies hatch in smaller numbers than do those in which such characters are present. 4. These facts are in accord with the principles and theories advanced by Morgan, and can be explained on a theory based on (1) the relative positions of factors in the chromosomes, (2) the twisting of homologous chromosomes about each other in gametogenesis, and (3) their subsequent splitting in one plane. 5. Further cytological evidence bearing on the above theory is much to be desired.