120 THE NORTH AMERICAN SPECIES OF DROSOPHILA. 



a dwarf is known. These mutants are to all appearances perfectly normal, 

 except in size. 



Eyes: The size of the compound eye shows great variation from species 

 to species. Figures 45 and 48 will illustrate this point. Similarly, the 

 mutant "eyeless" in D. melanogaster has eyes that are smaller than those 

 of the wild type. (As the name indicates, the eyes of this form are some- 

 times entirely gone.) Other mutant forms with small eyes are also known, 

 as well as a few in which the eyes are larger than those of the parent race. 



The wild species of Drosophila differ greatly in eye-color; and practically 

 all the colors found in them may be matched among the mutants of D. 

 melanogaster. D. repleta, D. virilis, and D. funehris have eyes that suggest 

 the purple or sepia mutants; D. willistoni and D. immigrans are nearer 

 scarlet or vermilion among the mutants. 



Bristles: The bristles of D. lutzii are decidedly smaller than those of most 

 species; this condition is paralleled by a number of mutant races in several 

 species. The postverticals are missing in Aulacigaster and in the mutant 

 races of D. melanogaster known as "scute" and "hairless." The vibrissse 

 are missing in Apsinota, in Idiomyia, and in the subfamily Chloropinse, and 

 elsewhere. Mr. D. E. Lancefield has discovered a mutant race of D. ohscura, 

 known as "deformed," in which these bristles are missing. The anterior 

 dorsocentrals are missing (or hair-like) in Mycodrosophila, in Drosophila 

 superha, and in the mutant race of D. melanogaster known as "two-bristle." 



Hairs: Hairs are present on the disk of the scutellum and on the meso- 

 pleura in the genus Curtonotum (and Apsinota ?) and in the mutant race of 

 D. melanogaster known as "hairy." A few bristles occur on the mesopleurse 

 of Aulacigaster and Camilla; aside from these and the usual four scutellar 

 bristles I know of no other instances in the subfamily in which these parts 

 bear bristles or hairs. 



Color: The general body-color of many of the wild species is darker than 

 that of D. melanogaster, of others paler and more yellowish. The same is 

 true of the mutant races, but it is difficult to match definite species with 

 given mutant colors, because the patterns are usually somewhat different. 

 Dark, smoky wings occur in such species as D. nehulosa, D. inversa, D. 

 annularis, D. opaca, and D. robusta. In these forms the pigment is usually 

 diffuse, but more concentrated along the veins. Somewhat smoky wings 

 with darker clouds along the veins also occur in the mutant races "black" 

 and "ebony." 



Wings: Slight differences in the shape of the wings are characteristic of 

 many of the wild species. D. immigrans, for example, has distinctly nar- 

 rower wings than has D. melanogaster. Similar slight differences occur 

 among the mutants. The types "broad" and "expanded" in D. melano- 

 gaster and "pointed" in D. funehris are examples. 



The numerous small wings among the mutants are of two different types. 

 In the first type ("miniature" in D. melanogaster, "short" in D. immigrans, 

 etc.), the parts are all present, but the wing is built on a small plan. This 

 type occurs in nature in such forms as the borborine Speomyia (Bezzi. 

 1914, Zool. Anz., 44, 504-506) and the scatopsid Coboldia (Melander. 

 1916, Bull. Wash. Agr. Exper. Sta., 130, 20). In the second mutant type 

 of wing, parts are missing. One gets the impression that pieces have been 

 cut away, leaving a part of a normal wing. Characteristic examples are 

 "vestigial," "strap," and "beaded" in D. melanogaster. The geomyzine 

 Mutilloptera (figured by Melander, 1916, Psyche, 20, 169) suggests strap, 

 and the chironomid Eretmoptera (Kellogg, 1905, Amer. Ins. p. 311) and 

 the tipulid Chionea (Washburn, 1905, Dipt. Minn. p. 38) suggest vestigial. 



