58 



Comparison of Characters 



D. melanogaster D. simulans 



yellow -. 

 prune -■ 



rubv 



0.0- 

 I. I- 



7. 5> 



-0.0 .. 

 -3.0 ■- 



yellow 

 prune 



11.3 -- rubyoid 



g 



arnet -- 44.4 



44.8 -- carmine 



D. obscura, D. simulans, and D. funehris. In all of these the charac- 

 ters are sex-linked and with one exception^ there are no autosomal 

 characters of this kind known. The maximum number of loci 

 involved is two, and two are repre- 

 sented in all but the last two 

 species. In D. melanogaster at least 

 five allelomorphs are known in the 

 forked locus, and two in the singed 

 locus (Mohr, 1922, and unpublished 

 data of C. B. Bridges). In each 

 case these express different degrees 

 of modification in the same direc- 

 tion. Similarly in D. willistoni two 

 ''forked" allelomorphs are known, 

 one being more extreme than the 

 other. 



The resemblance between these 

 characters in the different species is 

 so obvious as to suggest at once that 

 some homology exists between 

 them. Indeed, homology has been 

 demonstrated in the case of forked 

 melanogaster and forked simulans, 

 as noted above. But in the species 

 in which two non-alielomorphic 

 characters are concerned it is neces- 

 sary to find some distinction be- 

 tween the two before a comparison 

 can safely be made. Mohr (1922) fig. is.— x-chromosome maps of d. TTietono- 

 has given a detailed account of 

 forked and singed in D. melano- 

 gaster, and has indicated a series of differences between them. In 

 order to determine whether or not any of these differences will hold 

 constantly between the non-allelomorphic mutants of this type in 

 the other species, we have examined specimens of all of the available 

 mutants. These are included in the list on page 59, together with 

 those (in parenthesis) which we have not been able to examine (due 

 mainly to loss of the stocks). 



Before considering the relationships of these we may give brief 

 comparative descriptions of the different characters. These include 

 practically all of the features in which differences have been found. 

 Except where specified to the contrary the descriptions are based on 

 comparisons of male specimens side by side under the microscope. 



' A recessive, semi-lethal character in D. simulans (unpublished data of Dr. A. H. Sturtevant) 

 with stubby bristles, not unlike those of the less extreme stubby or forked mutants. 



forked -■ 56.3 



57. 2 -■ forked 



gastcr and D. simulans (from Sturtevant 

 1921a). 



