218 



THE AMERICAN NATURALIST 



[ Vol. L 



was obtained by averaging together the results of various 

 experiments not involving C, in which I had followed the 

 inheritance of both of the factors listed at the same time. 

 Many of the data listed in separate lines are of course 

 derived from the same experiment, as in most experi- 

 ments more than two pairs of factors were followed. It 

 should also be added that in one of the cases below (se 

 sps), the distance was slightly lengthened to allow for 

 coincident separations, the approximate proportion of 

 which was known, but the actual number of which had not 

 been determined in most of the crosses. 



Having determined the order of the factors, these re- 

 sults may now be combined, in order to obtain a series of 

 values based upon as many data as possible, and to con- 

 struct a diagram of the group. The diagram so made is 

 shown in Fig. 5. The numbers underneath the symbols 

 of the factors represent the * ' distance" of the latter from 

 sepia, which, as it lies at one end of the group, is used as 

 a common point of reference. Although the distances 

 shown will undoubtedly be subject to revision, the order 

 of all the factors shown, except deformed, band, and 

 beaded, is certain. Deformed (eye) is surely between 

 sepia and pink, but it is not yet quite certain that it is to 

 the right of dichaete; band (thorax) is near sooty, but on 

 which side is not known; beaded (wing) is very near 

 rough, but it has not been established whether it comes 

 before or after it (a count of 50 flies showed no crossing- 

 over between them). It was Sturtevant who first deter- 

 mined the position of beaded (found by Morgan, May '10) 

 with reference to this series (to the right of sooty), and 

 Bridges who first determined that dichaete lies between 

 sepia and pink (about 4 to the left of pink). The data 

 listed merely confirm these findings, so far as these two 

 factors are concerned. And it may here be repeated 

 that numerous other crosses of factors in this group have 

 also been made by these investigators, although the cros- 

 ses have not been of a sort to show the arrangement of 

 the factors studied. 



