18 Linkage Group I. 



bristles resemble singed, but the presence of forked is revealed by the dark, glossy 

 color of the thorax. Both sexes are fertile, but have poor viability. 



Origin. — A single male from a mating in which only one female parent was used. 

 (See Metz, 1916, p. 600.) 



Comparison. — (See p. 60.) 



Triangle (T). (Plate 2, Figures 5 and 6.) 



Description. — Triangle flies usually have an extra cross-vein between the costal 

 and second veins near their junction, and have the anterior cross-vein thickened at 

 its junction with the third vein (fig. 6, plate 2). The latter characteristic can usually 

 be detected in the few flies that fail to show the former. Sometimes the character 

 resembles the non-sex-linked dominant confluent. Triangle is a dominant character, 

 but is not lethal when homozygous. 



Origin. — The origin of triangle is not definitely known, since it was for a time 

 confused with branched, a non-sex-linked character. The separation of triangle from 

 branched was accomplished by Dr. Alexander Weinstein. 



Short (s). (Plate 2, Figure 7.) 



Description. — Short is more extreme in the males than in the females. In the 

 former the fifth vein is greatly shortened. Usually it does not extend much beyond 

 the posterior cross-vein, and frequently does not reach this vein. Approximately 

 half of the flies have the fourth vein slightly shortened also. In extreme cases the 

 cross-vein curves back to meet the fifth vein, or is curved back toward it, instead of 

 being straight. In the females the fifth vein is usually slightly shortened, but the 

 fourth is seldom affected, and often the wings appear to be normal. 



Origin. — (P. 384.) One male was obtained from a pair mating. 



Comparison. — Short resembles the character of the same name in D. vnllistoni 

 (Lancefield and Metz, 1922) and in D. obscura (D. E. Lancefield, 1922). 



Cut (ct). (Plate 2, Figures 8 to 10.) 



Description. — It should be noted in connection with the following description that 

 the gene for cut, if not allelomorphic to that for short, may be accompanied by short 

 in the same chromosome, and hence the effects described may be due to the com- 

 bination and not to cut alone. Cut flies, of both sexes, have short, narrow wings, 

 held at an angle from the body, and cut in at the apex, between the longitudinal 

 veins (fig. 8, plate 2). The cuts vary in depth from slight indentations to deep in- 

 cisions. The venation is irregular; the costal vein ends between the second and 

 third veins; the tips of the fifth, and sometimes of the other veins, are swollen, delta- 

 like; the second vein occasionally fails to reach the margin, and may fork at the 

 tip or send off a branch toward the third vein; the posterior cross- vein is usually 

 gone or broken; the anterior cross- vein is thickened, and lateral branches or swellings 

 frequently project from the longitudinal veins. The more common positions for the 

 latter are down from the second vein and from the fourth vein near the apex. Fre- 

 quently the wings are very small and are swollen or blistered. The anterior scutellar 

 bristles are usually gone, or small and slender, and the posterior scutellars are often 

 erect, or in abnormal positions, while the scutellum itself is shorter than usual. 



Cut flies do not breed readily, but both sexes are fertile to some extent and it is 

 possible to keep pure stock. 



In some (and possibly all) females heterozygous for cut, the tip of the fifth vein 

 is slightly thickened or delta-like (fig. 10, plate 2). This feature was overlooked at 

 first, hence we are not certain that it is constant. 



In females heterozygous for cut, and carrying short in the opposite X chromo- 

 some (possibly homozygous for short), the wings are smaller than usual, are held at 

 an angle from the body, and usually droop down over the sides; the tips of the fifth 



