No. 644] MUTANT CHARACTERS IN DROSOPHILA 233 



As far as possible the po- 

 sitions of the genes on the 

 ''map" have been determined 

 by summation of the "dis- 

 tances" between neighboring 

 loci taken in pairs, using 

 stubby arbitrarily as the zero 

 point. In several cases, how- 

 ever, the locus of a gene has 

 been assigned by reference 

 to some main well-established 

 point; notably, orange, forked, 

 scute, rough, or stump. In 

 Table VII, the starred data 

 are those on which the "map" 

 is based. No correction for 

 data involving non-adjacent 

 loci has been made, since the 

 degree of numerical accuracy 

 does not warrant such a com- 

 putation in this case. No cor- 

 rection has been made for 

 double crossing over in long 

 regions in which no mutant 

 loci are known. 



Owing to the possible par- 

 allelism between the yellow 

 and scute in imUistoni and 

 the yellow and scute in mela- 

 nogaster a second set of 

 readings has been given on 

 the "map" using the position 

 of yellow as the zero point and 

 plotting the others in opposite 

 ( + and — ) directions from 

 this. Comparison with the 

 X-chromosome map of mela- 

 nogaster is thus facilitated. 



