In a cross between purple-eyed[6] males and black females there appeared in F_2 (Nov. 4, 1912) a male having the veins of the wing arranged as shown in text-figure D b. It will be seen that the third and the fourth longitudinal veins are fused from the base to and beyond the {53} point at which in normal flies the anterior cross-vein lies. The cross-vein and the cell normally cut off by it are absent. There are a number of other features (see fig. D _c_) characteristic of this mutation: the wings are held out at a wide angle from the body, the ocelli are very much reduced in size or entirely absent, the bristles around the ocelli are usually small. The females are absolutely sterile, not only with their own, but with any males. Fused males by wild females gave wild-type males and females. Inbred these gave the results shown in table 32. The fused character reappeared only in the F_2 males, showing that it is a recessive sex-linked character. TABLE 32.--_P_1 fused [male] x wild [female][female]._ +-------------------------------------------------+ | First generation. | +------------+-------------------+----------------+ | Reference. | Wild-type | Wild-type ~ | | [female][female]. | [male][male]. ~ +------------+-------------------+----------------+ | 4I | 66 | 43 | | | | | +------------+-------------------+----------------+ +------------------------------------------------------------------+ | Second generation. | +------------+-------------------+----------------+----------------+ ~ Reference. | Wild-type | Wild-type | Fused | ~ | [female][female]. | [male][male]. | [male][male]. | +------------+-------------------+----------------+----------------+ | 190C | 258 | 96 | 115 | | 14I | 239 | 105 | 90 | | +-------------------+----------------+----------------+ | Total | 497 | 201 | 205 | +------------+-------------------+----------------+----------------+ The reciprocal cross was tried many times, but is impossible, owing to the sterility of the females. Since the fused females are sterile to fused males, the stock is kept up by breeding heterozygous females to fused males. By means of the following experiments the position of fused in the X chromosome was determined. A preliminary test was made by mating with eosin, whose factor lies near the left end of the X chromosome series. LINKAGE OF EOSIN AND FUSED. Fused (red-eyed) males mated to eosin (not-fused) females gave wild-type daughters and eosin sons, which inbred gave the classes shown in table 33.