Source of Material. 11 



"Achrosticlial hairs in six rows; no prescutellars. Mcsonotum and scutellum dark 

 dull-brown. Pleura; and abdomen dull brown, somewhat darker. Legs pale brown . 

 Apical and preapical bristles on first and second tibiae, preapicals on third. 



"Wings clear, veins brown. Costal index about 2.8; fourth-vein index about 1.8; 

 5x index about 1.2; 4c index about 0.9. 



"Length body 2.8 mm.; wing 3.0 mm. 



"The eggs have four filaments. The females do not ordinarily begin to lay until 

 they are 4 or 5 days old. About 3 weeks are required for development. 



"The small eyes and broad cheeks make this species obviously distinct from such 

 types as D. robusta that resemble it superficially." 



Supplementary to the above, especial attention may be called to 

 certain characteristics that are particularly noticeable in living 

 specimens or that need to be kept in mind in considering the com- 

 parison of mutant characters with those of other species: The dark 

 dull-brown body-color and large size of D. virilis contrast sharply 

 with the yellowish gray color and small size of such species as D. 

 melanog aster, D. simulans, and D. willistoni. The color more nearly 

 resembles that of D. ohscura, but is duller and lighter. It is duller 

 and darker than that of D. funehris and lacks the olive tone of the 

 latter. The eyes of D. virilis are dark, dull, reddish brown, more 

 opaque than those of melanog aster, simulans, willistoni, or ohscura. 

 Virilis males do not possess the tarsal "sex-combs" found in 

 melanogaster, simulans, and ohscura. In this respect they agree with 

 the males of willistoni and funehris. A wild-type or normal male 

 of D. virilis is shown in figure 1 of plate 1. 



SOURCE OF MATERIAL. 



The original stock of Drosophila virilis Sturtevant, used in our ex- 

 periments, was derived from a single pair hatched from a pineapple 

 exposed at Columbia University, in November, 1913, by Dr. A. H. 

 Sturtevant, Nearly all of our work has been based on descendants of 

 this one pair, which have been kept in the laboratory, in bottles, for 8 

 years, or approximately 136 generations. In 1919 a second stock col- 

 lected at Terre Haute, Indiana, was obtained from Dr. Roscoe Hyde. 

 One mutant character (hump) was found in this stock soon after it 

 was secured and others appeared subsequently. The two stocks have 

 been more or less intercrossed in the course of the experiments. 

 They appear to be identical in all respects and we have made no 

 effort to keep them separated. 



Since no other records of this species are known save one from 

 Los Angeles, California, and one from a doubtful specimen taken at 

 Chattanooga, Tennessee (Sturtevant, 1. c, p. 97), it is practically 

 certain that our stocks have never been contaminated from sources 

 outside the laboratory. 



It may be noted in this connection that no decrease in fertility 

 has been observed in the stocks during their 8 years' confinement 

 in the laboratory. 



