1924 ] 
The Biology of Trichopoda pennipes Fab. 
61 
generalized insects. The work of Peterson (1916) on the mouth 
parts of Diptera was very thorough, and his figures correct and 
intelligible, but since he derives his hypothetical dipterous 
mouth parts from a consideration of Orthoptera while Crampton 
(1921, p. 91) would evolve Diptera from ancestors like Mecop- 
tera, the homologies of dipterous mouth parts still constitute a 
disputed question. 
The membrane of the basiproboscis (bpb) is largely composed 
of the mentum and sub-mentum, according to Peterson. The 
maxillary palpi; (mxp) lie on this membrane in front. Above the 
maxillary palpi lie the exposed portions of the tormse (to), and 
below lie the external plates of the stipes (st). The galeae (ga) 
lie on the surface, and are continuous with the lower ends of 
the ental portions of the stipes. The large chitinous internal 
structure of the basiproboscis is the fulcrum (ful) and is com- 
posed of the basipharnyx, or united portions of the epipharynx 
and hypopharynx, and the ental portions of the tormse. At the 
distal end of the basipharynx lies the hyoid (hy), which articulates 
with the distal portion of the hypopharynx as well, and through 
which passes the alimentary canal. 
The mediproboscis (mpb) bears the chitinized plate, the 
theca (the), on its caudal aspect, and the hypopharynx (hyp) 
and labrum-epipharynx (lep) lie in a chitinized groove on the 
upper surface of the labium. 
The distiproboscis (dpb) is composed of a pair of lobc-s or 
labella, which Peterson interprets as the paraglossae (pg). 
Crampton, however, calls them the united labial palpi. Various 
other structures can be seen in the distiproboscis, such as a 
Y-shaped plate called the furca (fu) and the structures called 
pseudotrachse (pst). 
Thorax. PI. I, figs. 3 and 4. The structure of the thorax 
in Trichopoda pennipes is typical of the order Diptera as a whole, 
in which the mesothorax, which is the only wing-bearing seg- 
ment, is greatly enlarged and distorted, evidently for the purpose 
of accomodating the great wing muscles. The prothorax (P) 
is very small, and the metathorax, which bears the halteres(ha), 
jg very much reduced. 
