The data show that the factor for fused lies about 3 units to the right of bar. This is the furthest point yet obtained to the right. The reasons for locating fused to the right of bar are that, if it occupies such a position, then the double cross-over classes (which are expected to be the smallest classes) should be vermilion bar and fused, and these are, in fact, the smallest classes. The order of factors is, then, vermilion, bar, fused. This order is confirmed by the result that the number of cross-overs between fused and vermilion is greater than that between bar and vermilion. In order to obtain data to balance viability effects, the following experiment was made: Vermilion (not-bar) fused males were bred to (red) bar (not-fused) females. The daughters and sons were bar. The daughters were back-crossed, singly, to vermilion fused males and gave the results shown in table 35. Each female was also transferred to a second culture bottle, so that for each female there are two broods given consecutively (82, 82', etc.) in table 35. The results given by the two broods of the same female are similar. The values are very near to those given in the last experiment, and confirm the conclusions there drawn. The combined data give the results shown in table 36. {56} TABLE 35.--_P_1 bar [female] [female] x vermilion fused [male] [male]. B. C. F_1 bar [female] x vermilion fused [male] [male]._ A - Vermilion fused. B - Bar. C - Vermilion bar. D - Fused. E - Vermilion. F - Bar fused. G - Vermilion bar fused. H - Wild type.