ANATOMY. 35 



the only clasper present in most Drosophilinae, must be the anterior 

 clasper of the Calypterse. 



The three plates just discussed — the genital arch, the clasper, and 

 the anal plate — together with the soft parts around them, form what 

 is known as the hypopygium. These plates furnish extraordinarily 

 certain and definite specific characters, but can not be studied satis- 

 factorily except in cleared or dissected material. I have therefore 

 avoided their use, except in the case of Drosophila melanogaster and 

 D. simulans. In this case I have been unable to discover any more 

 convenient character for separating the two species. Their use will 

 undoubtedly be necessary when a satisfactory treatment of the genus 

 Chymomyza is worked out. 



Internal genital apparatus, male: The penis is a chitinized tube, 

 differing greatly in shape from species to species. It can be extruded 

 through the genital opening, between the lower ends of the genital 

 arch. In the genus Curtonotum it is long and strongly curved, sug- 

 gesting the coiled penis of the Trypetinse. Within the body lie other 

 chitinized parts connected with the penis, but I have not made out 

 their nature and detailed structure. 



The testes are usually cylindrical and coiled, but are ellipsoidal in 

 Drosophila ohscura. They are usually bright-colored — reddish-orange 

 to yellow, according to the species. In the adult male of most members 

 of the group the testes contain chiefly fully formed spermatozoa. 



Fig. 17. — Oblique section through spermatheca of Drosophila obscura, 



showing sperm inside. 



Internal genital apparatus, female: In the abdomen of the female 

 are to be found small chitinized seminal receptacles or spermathecce 

 (figs. 18 to 43). The figures will give an idea of the types that occur. 

 Leading from each receptacle is a trachea-like tube that opens into the 

 oviduct. Figure 17 shows an oblique section through a spermatheca 

 that is filled with spermatozoa. The number of these receptacles is 

 two in all but two of the drosophiline species that I have examined. 

 These include one species each in the genera Curtonotum, Zygothrica, 

 Zaprionus, Leucophenga, and Mycodrosophila, two each in Scaptomyza 

 and Chymomyza, and 22 in Drosophila (including such widely divergent 

 forms as D. busckii, D. guttifera, D. immigrans, D. nebulosa, and D. 

 saltans). Among these 31 species the only strikingly different types 

 of receptacles found were in Leucophenga varia (fig. 19), and in Curto- 

 notum gibhum, in which they are narrow, smooth, and cylindrical. 

 The two exceptions to the rule that two chitinized receptacles are 

 present are Drosophila inversa, in which I have been unable to find 



