ANATOMY. 515] 
the only clasper present in most Drosophiline, must be the anterior 
clasper of the Calyptere. 
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 Trypetine. 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 obscura. 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. 
Fic. 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 spermathece 
(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 gibbum, 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 
