1. Fifteen factors have been located on four out of the twelve chromosomes. Some other linkages are suspected, and a new case of multiple allelomorphism or very close linkage is described.

2. As compared withDrosophila, interference is definitely less marked, though it certainly occurs.

3. In two regions linkage is tighter on the male than on the female side, in two looser, while in two others it is nearly the same. Apart from this the figures are inadequate for a judgment.

4. In one chromosome the genetical data from the tetraploid permit the rough location of a spindle attachment.

5. The linkage values found in different families show a remarkable constancy.

6. New mathematical methods are given for dealing with goodness of fit, combination of linkage data, and allowance for double cross-overs when mapping.