The evidence from the history of the stock, together with these experiments, shows that the character resembles club (wing) in that it is not expressed somatically in all the flies which are homozygous for it. In the case of club we were fortunate enough to find a constant feature {46} which we could use as an index, but, so far as we have been able to see, there is no such constant accessory character in the case of the dot. Unlike club, dot is markedly sex-limited in its effect; that is, there is a difference of expression of the gen in the male and female. This difference recalls the sexual dimorphism of the eosin eye. BOW. In an F_2 generation from rudimentary males by wild females there appeared, August 15, 1912, a single male whose wings instead of being flat were turned down over the abdomen (fig. c). The curvature was uniform throughout the length of the wing. A previous mutation, arc, of this same type had been found to be a recessive character in the second group. The new mutation, bow, is less extreme than arc and is more variable in the amount of curvature. When the bow male was mated to wild females the offspring had straight wings. [Illustration: FIG. C.--Bow wing.] TABLE 21.--_P_1 bow [male][male] x wild [female][female]._ +------------------------------------------+ | First generation. | +----------+-----------------+-------------+ |Reference.| Wild-type | Wild-type ~ | |[female][female].|[male][male].~ +----------+-----------------+-------------+ | 169 C. | 17 | 17 | +----------+-----------------+-------------+ +--------------------------------------------------------+ | Second generation. | +----------+-----------------+-------------+-------------+ ~Reference.| Wild-type | Wild-type | Bow | ~ |[female][female].|[male][male].|[male][male].| +----------+-----------------+-------------+-------------+ | 18 I. | 193 | 145 | 67 | | 21 I | 182 | 100 | 49 | | +-----------------+-------------+-------------+ | Total.| 375 | 245 | 116 | +----------+-----------------+-------------+-------------+ {47} The F_2 ratio in table 21 is evidently the 2:1:1 ratio typical of sex-linkage, but with the bow males running behind expectation. This deficiency is due in part to viability but more to a failure to recognize all the bow-winged individuals, so that some of them were classified among the not-bow or straight wings. In favor of the view that the classification was not strict is the fact that the sum of the two male classes about equals the number of the females. BOW BY ARC.