18 



Mohr. 



Table 6. Pi, hairy oo X Star Dichaete dcf; B.C., 

 Fl Star Dichtete o X hairy cf cT. 



work informs me that he has found the first alternative to be the 

 correct one. According to his data the hairy locus is at 25.8 or half 

 a unit to the right of sepia. 



Hairy is one of the most striking examples of the comparatively 

 rare mutations representing an actual addition to the original structure 

 of the species. It should be mentioned that, according to Dr. Sturte- 

 vant ('21), the presence of mall hairs on the scutellum is typical of the 

 genus Curtonotum. This alteration thus represents one of the specific 

 cases of parallelism between mutant characters and characters of wild 

 species. 



Hairy flies are of excellent viability and can be separated with 

 perfect accuracy and ease from the wild type. In one respect the 

 character is also exceptionally favorable: it does not interfere with any 

 other known mutant character in Drosophila. 



Forked-. 



In making up the selected singed stock, it was observed (May 7, 

 1919) that one of the not singed males showed a slight alteration of 

 the posterior scutellar bristles. They were bent at sharp angles near 

 the end, and one of them showed in addition a bifurcation. The affec- 

 ted bristles were slender and tapered like the rest of the macrochsetae. 



It was suspected that the bristle alteration might be due to a 

 gene which was allelomorphic to forked; and the male was therefore 

 crossed to females homozygous for the sex -linked dominant Bar, the 

 locus of which is very close to that of forked. One of the Fi daughters 

 was back-crossed to her own father, while another was crossed to Bar 

 males (Table 7). 



