A. H. STURTEVAXT AND C. R. PLUXKETT. 



for A or for H, since the somatic effects produced by these genes 

 are in many respects on the same characters but in opposite 

 directions, so that heterozygosis for one of them might con- 

 ceivably tend to counteract the lethal effect of the other one. 

 Since all the melanogaster-simulans hybrids are sterile, it was not 

 possible to test this exceptional individual. In any case, this 

 one specimen cannot vitiate the conclusion that both delta and 

 hairless are corresponding genes in the two species. 



ru 

 



56 

 26 



st p 



AH 



66 695 





ca. Mi} 

 101 loS 



meUno^dster 



6 



cu se 



st 



57 60 



HA 



101 

 P 



13C 



ca 



simuUns 



FIG. i. 



Fig. I shows the linkage relations of the six corresponding 

 genes in the two species, together with the left-most and right- 

 most known loci of each species. 



The melanogaster map is based on the values given by Bridges 

 and Morgan (1923). The simulans map is based on unpublished 

 data, including counts from crosses involving several genes not 

 here recorded. The intervals in this map are not yet accurately 

 determined, because of a lack of favorable mutations; but they 

 are more likely to be lengthened than to be shortened by further 

 data. -The sequence of the corresponding genes in simulans is 

 clearly established, as the following data will show. Claret 

 cannot be distinguished somatically from peach, so its position 



TABLE I. 



st 



se + A 



9 Xsest + <?. 



