146 OTTO L. MOHR 



were typically curled, ^vllile the rest of the individual including prac- 

 tically the whole head had ordinary wild-type hairs and bristles like 

 the other flies in this stock. 



In the stock mentioned homozygous black purple curved females, 



(/,- 1, are in each generation crossed to males that in one of 



\l)l pr cuy ^ 



their Il-chromosomes carry the same récessives and in the other 



Streak and curved and in addition also some other Il-chromosome 



récessives, which are of no special interest in this connection, 



j -J, — ^; I [hi, black body color; pr, purple eyes; cii, curved wings; 



Sk, dark streak on thorax. Sk is dominant and lethal when homo- 

 zygous, the rest are récessives; all are located in the Il-chromosome). 

 The males used in the mating are accordingly somatically Streak 

 curved. Since there is no crossing over in the male this cross gives 

 in the next generation bl pr en and Sk cii invidiuals in equal numbers, 

 and the stock is maintained unchanged by repeating in each genera- 

 tion the mating described. It should be emphazised that the stock 

 never had contained sex-linked mutant genes and that none of the 

 genes present in the stock produce bristle and hair alterations. 



When the male mosaic was found the whole contents of the 

 stock bottle was carefully examined, and 35 females and 31 males 

 were counted, which were all either bl pr cii or Sk cii. None of them 

 exhibited any bristle or hair alteration. 



A scrutinous examination of the exceptional individual gave the 

 following result (see Fig. 1 — 3). The fly showed the typical male cha- 

 racters (normal male external genitalia, sex combs on both fore legs, 

 male coloring of the abdomen, smaller size). The wings were curved. 

 It was somewhat difficult to ascertain, whether the thorax exhibited 

 the mutant character Streak. The fly was apparently young, and 

 the Streak character, which is rather variable, is most easily detected 

 in older individuals. The fly was non-black and non-purple. 



The head had normal slender and tapered bristles and hairs, 

 except in a narrow ventro-lateral part on the right side, (the bucca). 

 This plate bears at its anterior end the vibrissae or oral bristles. 

 The latter were on the right side typically singed, in striking contrast 

 to those on the left side. Also the hairs and bristles along the lower 

 posterior edge of the bucca were singed on the right side, while the 

 hairs along the cheek were wild-type on both sides. 



The bristles and hairs on the left side of the thorax were typically 



