64 



Comparison of Characters 



factorial relations are shown on the accompanying chromosome 

 maps (fig. 16), with the exception of depressed, which is an autosomal 

 character. 



Comparison with Sex-Linked Characters in Drosophila simulans. 



Turning to the sex-linked characters of other species than mela- 

 nogaster, we find first the parallels yellow and forked in D. simulans. 

 Since these are homologous to the yellow and forked in melanog aster 

 the above discussion covers their 

 case. A third character, bubble, in 

 simulans parallels vesiculated in 

 virilis both in appearance and in its 

 map locus. This type of character, 

 like many of the eye-colors, is not 

 very reliable for comparison, but, 

 so far as the evidence goes, it points 

 towards homology. 



D. melanogaster 



D. virilis 



0. -- 



13.2 



21.0 -~ 



Comparison with Sex-Linked Char- 

 acters in D. willistoni. 



56.5 --, 



70.0 



— yellow^ 



71 



forked' 



In D. willistoni, the four char- 

 acters yellow, vermilion (unpub- 

 lished), forked, and stubby resem- 

 ble, respectively, yellow, vermilion, 

 singed, and forked in virilis, and the 

 order and relative positions of their 

 loci on the map are similar, except 

 that in willistoni the series begins 

 (with yellow) at approximately the 

 middle of the map instead of at the 

 end. The latter fact has suggested 

 (of. Lancefield and Metz, 1922) that 

 the large, V-shaped X chromosome 

 of willistoni may represent the rod- 

 like X of melanogaster and virilis 

 plus another rod of equal length at- 

 tached at its end. This is in agree- 

 ment with the apparent chromoso- 

 mal relations of these species, and 

 with the interpretation given by D. 

 E. Lancefield for similar conditions 

 in D. ohscura. A sex-linked ''crossveinless" has also been found 

 recently in willistoni, and its locus is very close to that of vermiUon, 

 as is the case in virilis. Whether it is above or below vermilion has 

 not yet been determined. It will be recalled that the vermilion 



-- 6 



crossveinless.. 



~-- 24 



singed.. 



-- 42 



109 



Figure 15. 



X-chromosome maps of Drosophila melano- 

 gaster and D. virilis, indicating loci of ^ 

 "parallels" (see text). 



