The factors (lethal 1, white, facet, abnormal, notch, and bifid) which lie close to yellow were the first to be calculated and plotted. The next step was to determine very accurately the position of vermilion with respect to yellow. There are many separate experiments which influence this calculation and all were proportionately weighted. Then, using vermilion as the fixed point the factors (dot, reduplicated, miniature, and sable) which lie close to vermilion were plotted. The same process was repeated in locating bar with respect to vermilion and the factors about bar with reference to bar. The last step was to interpolate the factors (club, lethal 2, lemon, depressed, and shifted), which form a group about midway between yellow and vermilion. Of these, club is the only one whose location is accurate. The apparent closeness of the grouping of these loci is not to be taken as significant, for they have been placed only with reference to the distant points yellow and vermilion and not with respect to each other; furthermore, the data available in the cases of lemon and depressed are very meager. The factors which are most important and are most accurately located are yellow, white (eosin), bifid, club, vermilion, miniature, sable, forked, and bar. Of these again, white (eosin), vermilion, and bar are of prime importance and will probably continue to claim first rank. Of the three allelomorphs, white, eosin, and cherry, eosin is the most useful. {24} NOMENCLATURE. The system of symbols used in the diagrams and table headings is as follows: The factor or gen for a recessive mutant character is represented by a lower-case letter, as v for vermilion and m for miniature. The symbols for the dominant mutant characters bar, abnormal, and notch are B', A', and N'. There are now so many characters that it is impossible to represent all of them by a single letter. We therefore add a subletter in such cases, as bifid (b_i), fused (f_u), and lethal 2 (l_2). In the case of multiple allelomorphs we usually use as the base of the symbol the symbol of that member of the system which was first found and add a letter as an exponent to indicate the particular member, as y^s for spot, w^e for eosin, and w^c for cherry. The normal allelomorphs of the mutant gens are indicated by the converse letter, as V for not-vermilion, B_i for not-bifid, and b' for not-bar. In the table headings the normal allelomorphs are indicated by position alone without the use of a symbol.