STURTEVANT 



137 



Table 20 

 f B f „ crossing over 



published on these loci are included 

 vvath the above, in order to arrive at 

 final "map values" for the three loci. 

 On the basis of these data, it seems 

 best to map forked 0.2 unit to the left 

 of bar, that is, at 56.8; and fused 2.5 

 units to the right of bar, at 59.5, thus 

 making the forked-fused interval 2.7 

 units. 



FACET NUMBER 



It has been shown by Zeleny and 

 Mattoon (1915), May (1917) and 

 Zeleny (1922) that selection for num- 

 ber of facets is effective in isolating 

 lines of bar flies with high facet num- 

 bers or with low. Though no detailed 

 genetic analysis has yet been reported, 

 there is abundant evidence in these 



Table 21 



f f „ crossing over 



papers that ordinary bar stocks are 

 heterogeneous for modifiers (not in 

 the bar locus) that affect facet num- 

 ber. This is also the impression I have 

 gained from extensive but less exact 

 studies, with numerous crosses in- 

 volving bar. 



Another source of variability in 

 facet number is temperature. It was 

 shown by Seyster (1919) that high 

 temperature decreases the facet num- 

 ber of bar, and this relation has been 

 studied in great detail by Krafka 



(1920), Zeleny (1923), A. H. Hersh 

 (1924) and R. K. Hersh ( 1 924) . These 

 observers have shown that the effect 

 is present, though in var\ang degree, 

 in double-bar, round, and in various 

 heterozygotes, as well as in bar. Al- 

 though these studies furnish essential 

 data for any complete analysis of the 

 mode of action of the bar series of 

 allelomorphs upon development, they 

 need not be further discussed here. 

 The evidence just reviewed indi- 

 cated that it would be necessary to get 



