NEW DATA. 27 



other, with the single exception of white. While the wings of miniature 

 usually extend backwards, they are sometimes held out at right angles 

 to the body, and especially in acid bottles the miniature flies easily 

 become stuck to the food or the wings become stringy, so that other 

 wing characters are not easy to distinguish in those flies which are also 

 miniature. At present vermilion, whose locus is at 33, in being used 

 more frequently in linkage work. The locus of miniature at 36.1 is 

 slightly beyond the middle of the chromosome. 



VERMILION. 



(Plate II, figure 10.) 



The recessive sex-linked mutant vermilion eye-color (Morgan, 191 ic 

 and 191 20) appeared in November 1910, and has appeared at least 

 twice since then (Morgan and Plough, 1915). This is one of the best 

 of the sex-linked characters, on account of its excellent viability, its 

 sharp distinction from normal with very little variability, its value as 

 a double recessive in combination with other sex-linked eye-colors, 

 and because of its location at 33.0, very near to the middle of the known 

 chromosome. 



YELLOW. 



(Plate I, figure 5.) 



The recessive sex-linked mutant yellow body and wing-color ap- 

 peared in January 1911 (Morgan, 191 ic and 1912^). Its first appear- 

 ance was in black stock; hence the fly was a double recessive, then 

 called brown. Later the same mutation has appeared independently 

 from gray stock. Yellow was found to be at the end of the X chromo- 

 some, and this end was arbitrarily chosen as the zero or the "left end," 

 while the other gens are spoken of as lying at various distances to the 

 right of yellow. Recently a lethal gen has been located less than one- 

 tenth of a unit ( 0.04) to the left of yellow, but yellow is still retained 

 as the zero-point. 



The viability of yellow is fairly good and the character can be sepa- 

 rated from gray with great facility, and in consequence yellow has been 

 used extensively, although at present it is being used less than formerly, 

 since eosin lies only i.i units distant from yellow and is generally 

 preferred. 



ABNORMAL ABDOMEN. 



(Plate I, figure 4.) 



The dominant sex-linked character abnormal abdomen appeared in 

 July 1911 (Morgan, 191 id). It was soon found that the realization of 

 the abnormal condition depended greatly upon the nature of the envi- 

 ronment (Morgan, 1912). Recently a very extensive study of this 

 character has been published (Morgan, 1915). As this case has been 

 reviewed in the introduction, there is little further to be said here. 



