72 



Comparison of Maps. 



loci are relatively crowded as compared with those of virilis and 

 obscura, in which almost as many loci are represented. The dif- 

 ferences seem to be largely due to general increase or decrease in 

 crossing-over, but it is probable that some regions in the chromosomes 

 differ more than others in this respect. This has been shown to be 

 the case in D. simulans (Sturtevant, 1921a), and is indicated in the 



D.willistoni D. obscura 



■ -short 



0. simulans 



D.virilis 



O.melanogaster 



Yellow — 

 - Prune ^^ 



Rubyoid- 

 bubble 



Carmine - 



Forked - 



Scute., 

 , xYellow, 

 irPrune 

 <White 



Notch 



Ruby 



Crossveinless, 



Singed, 



■lozenge »_ 

 --Vermilion 



Garnet 



inflated 

 Forked, 



sepia 



VVnow- 



Crossveinless . 

 4^ Vermilion / 

 esiculated' 



'■-Singed' 



Scute-. 

 .Veiiow- 



Vecmilion 



■ Forked ^ 



-Stubby 



•magenta' ,-' 

 '•}■ Forked" 



short 



glazed 

 droop 



O.funebrJs 



Scutellar 

 ''Jfellow 



Notch 

 vvh.te 



- -Vermilion 

 -Singed ' 



Notch 



Forked 



stubby ' 

 - -short 

 stubby' 



Figure 16. — X-chromosome maps of six species of Drosophila drawn to scale 

 according to cross-over percentages. 



