203] HEAD OF DIPTERA— PETERSON 33 



distiproboscis. These terms have here been adopted. The basiproboscis 

 (bpr) is equivalent to the rostrum, and may be defined as the mem- 

 branous, cone-shaped area between the ventral margin of the head- 

 capsule and the proximal end of the theca. The tormae, labrum- 

 epipharynx, hypopharynx, and maxillae are parts of the basiproboscis. 

 The mediproboscis (mpr) is the median section of the proboscis and 

 includes the theca and the chitinized cephalic groove of the labium. It 

 is equivalent to the haustellum of most authors. The distiproboscis 

 (dpr), the enlarged dilated lobes at the distal end of the proboscis, is 

 composed of the paraglossae, with their pseudotracheal areas, and the 

 glossae. The distiproboscis is equivalent to the oral lobes, or labellae. 

 The movable appendages of the head are discussed in the following 

 order: antennae, mandibles, maxillae, and labium. 



Antennae. — The antenna of a generalized hypothetical dipterous 

 head (Fig. 199h) is many-segmented and of a filiform type. All the 

 segments are similar excepting the two large proximal ones known as 

 the scape (sc) and the pedicel (pd). The scape articulates with the 

 chitinized antennal sclerite (a. s) which bounds the periphery of the 

 antenual fossa (a. f ) that is situated on the vertex dorsad of the arms 

 of the epicranial suture. The antennae of the hypothetical type resem- 

 ble the antennae of many generalized insects. 



The antennae of a majority of the Nematocera resemble the hypo- 

 thetical type, and on the whole resemble each other. The variations in 

 shape and size can be seen in the figures. Secondary sexual variation 

 occurs in a few of the Nematocera, in which the antennae of the male, 

 illustrated by Chironomus (Fig. 207) and Psorophora (Fig. 211), bear 

 long flexible setae while those of the female are almost bare. 



The antennae of the Brachycera show a wide range of development, 

 but in a majority of the genera figured the main line of specialization 

 is toward the type found in Lonchoptera (Fig. 223) and Dolichopus 

 (Fig. 226). One of the striking exceptions to this general line of de- 

 velopment occurs in the geniculate type found in Stratiomyia (Fig. 

 213). The antennae of the Brachycera have, as a rule, fewer segments 

 than the Nematocera. The scape and pedicel undergo only a slight 

 change, in this group, but the flagellum (fl) is greatly modified. The 

 proximal segment of the flagellum, or the third segment of the antenna, 

 is enlarged, while the remaining segments are so reduced in size as to 

 resemble the lash of a whip. The lash-like portion of the antenna is 

 called the arista (ar). The following genera suggest the various stages 

 thru which the antennae have passed in attaining the muscid type of 

 development. In Tabanus (Fig. 214), Empis (Fig. 215), Exoprosopa 

 (Fig. 216), Promachus (Fig. 217), and Leptis (Fig. 218) the flagellum 



