4 Mohr. 



and accordingly three purple singed males from 558 were crossed in 



mass cultures to eight females, half of which, according to the cross 



from which they were derived, were expected to be heterozygous for 



forked. If we were dealing with a reappearence of the old forked gene 



or with an allelomorph some of the females originating from this cross 



would be forked, having received one forked gene from their father and 



one from their heterozygous mother. The mass culture gave 151 females, 



all wild-type; 105 wild-type and 32 forked males (584, Oct. 15, 1918). 



The absence of forked females proved that the new gene was not 



identical with or allelomorphic to the old forked gene. We were 



dealing with a new mutant gene, located somewhere else in the X- 



chroiiiosome. The singed males were now more carefully examined and 



it was found that the character possessed somatic peculiarities which 



made a separation from forked flies easy. 



• 



DescriptioD of siDged. 



The description of the character forked given by Morgan and 

 Bridges ('16) is as follows: "The large bristles (niacroch?et?e), instead 

 of being long, slender and tapered, are greatly shortened and crinkled 

 as though scorched. The ends are forked or branched, bent sharply or 

 merely tickened. The bristles wliich are most disorted are those upon 

 the scutellum, where they are sometimes curled together in balls." 

 The alteration is present in the large bristles throughout the body, 

 but the small hairs all over the body are entirely unaffected. 



The macroch?etjTe upon the head and thorax of the singed fly are 

 somewhat shortened and thickened but not as much so as they are in 

 forked flies. On the other hand they are much more pronouncedly curled, 

 those on the scutellum often being curled together into balls. Not a 

 single bristle upon the whole body is unaffected. The curled bristles 

 are sometimes also branched, but not very often. The sharp bending 

 which is so typical in forked flies is rarely seen in singed individuals 

 (Fig. 1). 



The somatic feature which makes separation of singed from forked 

 certain is the fact that the characteristic curling also extends to all 

 the tiny hairs upon the thorax and all the small hairs ail over the 

 body. The only small hairs which are not distinctly affected are those 

 around the wing margin. In the wing the singed character may there- 

 fore be recognized only in the two somewhat larger hairs on the costa, 

 just before the apex of the first vein. 



