Thus the symbol [draw] indicates that the female in question carried eosin, not-vermilion, and bar in one chromosome and not-eosin, vermilion, and not-bar in the other. The symbol [draw] when used in the heading of a column in a table indicates that the flies classified under this heading are the result of single crossing-over between eosin and vermilion in a mother which was the composition [draw]; the symbol tells at the same time that the flies that result from a single cross-over between eosin and vermilion in the mother are of the two contrary classes, eosin bar and vermilion. When a fly shows two or more non-allelomorphic characters the names are written from left to right in the order of their positions from the zero end of the map. * * * * * {25} PART II. NEW DATA. WHITE. (Plate II, figure 11.) The recessive character white eye-color, which appeared in May 1910, was the first sex-linked mutation in _Drosophila_ (Morgan, 1910_a_, 1910_b_). Soon afterwards (June 1910) rudimentary appeared, and the two types were crossed (Morgan, 1910_c_). Under the conditions of culture the viability of rudimentary was extremely poor, but the data demonstrated the occurrence of recombination of the factors in the ovogenesis so that white and rudimentary, though both sex-linked, were brought together into the same individual. The results were not fully recognized as linkage, because white and rudimentary are so far apart in the chromosome that they seemed to assort freely from each other. Owing to the excellent viability and the perfect sharpness of separation, white was extensively used in linkage experiments, especially with miniature and yellow (Morgan, 1911_a_; Morgan and Cattell, 1912 and 1913). White has been more extensively used than any other character in _Drosophila_, though it is now being used very little because of the fact that the double recessives of white with other sex-linked eye-colors, such as vermilion, are white, and consequently a separation into the true genetic classes is impossible. The place of white has been taken by eosin, which is an allelomorph of white and which can be readily used with any other eye-color. The locus of white and its allelomorphs is only 1.1 units from that of yellow, which is the zero of the chromosome. Yellow and white are very closely linked, therefore giving only about one cross-over per 100 flies. All the published data upon the linkage of white with other sex-linked characters have been collected into table 65. RUDIMENTARY.