34 CONNECTICUT GEOL. AND NAT. HIST. SURVEY [BllU. 



The maxillary palpi, mp\ are best developed in the Nematocera, 

 and the third segment of the palpus bears a peculiar sense organ, so, 

 in such Nematocera as Edwardsina (Fig. 2, J), Anisopus (Fig. 2, K), 

 etc., like that of the mecopteron Nannochorista (Fig. 2,1). In the 

 Nematocera, the palpal segments may vary from one, in such tipulids 

 as Gonosia and Ilexatoma, to five in the tanyderids (Fig. 2, H) and 

 the culicids (Fig. 3, E) . According to Williston (1909, p. 26) , "Theo- 

 bold says that some Culicidae have six (palpal) joints, but his state- 

 ment needs confirmation." The supposed sixth palpal segment de- 

 scribed by Theobold may possibly be the palpifer, p/r, of the culicid 

 Anopheles shown in Fig. 3, E. This culicid, and the tanyderid shown 

 in Fig. 2, H, are the only Diptera in which a true palpifer has been 

 observed, and it is very probable that the so-called palpifer of fe- 

 male tabanids is merely a prolongation of the stipital region of the 

 maxilla. There is usually only one segment in the palpi of the bra- 

 chycerous Orthorrhapha and the Cyclorrhapha, and this becomes re- 

 duced to a small vestige in Mydas (which preserves the maxillary 

 galea), and is completely lost in Gonops^ although a vestige of the 

 galea is preserved in the latter insect. The maxillae are so greatly 

 reduced in the higher Diptera, and their parts are so highly modified, 

 that many of the earlier observers were unable to interpret these struc- 

 tures correctly; and investigators, such as Wesche (1909), have inter- 

 preted the maxillary galeae as the "palpi" of the maxillae, and have 

 consequently interpreted the true maxillary palpi as "labial" palpi, 

 etc. 



The labium, ?^, is usually the largest of the mouth parts, and fre- 

 quently forms a trough or "gutter" in which the other mouth parts lie. 

 The labium of the lower Diptera is strikingly similar to that of the 

 mecopteron Nannochorista (Fig, 2,1), and a comparison between the 

 two types of insects is veiy instructive for interpreting the parts in 

 the Diptera, 



The mentum, nvn, is developed as a distinct plate in some species 

 of Anisopus (Fig. 2, K). The mentum, mn, is extremely elongated in 

 Tanydems (Fig. 2, H), and resembles that of the mecopteron Harpo- 

 hittacus (Fig. 2, E) in this respect. In Asyndulum (Fig. 2, C) the 

 mentum, mn, forms the median region of the stipital plate, whose lat- 

 eral portions are formed by the stipites, sti\ and in Tanyderus (Fig, 

 2, H) the stipites, sti, likewise tend to unite with the elongated men- 

 tum. 



The prementum, pin, which is one of the most important of the 

 labial sclerites, is formed by the union of the columnar sclerites called 

 the "palpigers" in the labium of the Coleoptera, but these sclerites in- 

 clude a large portion of the labial stipites as well, — and in fact are 

 largely composed of the labial stipites. A suture, or a deep groove, 

 which marks the line of union of the two parts of the prementum, pm, 

 is preserved in the labium of many primitive Diptera (Fig. 2, C), but 

 nothing like this occurs in a typical mentum, mn (Fig. 2, K), which is 

 typically a single undivided plate, so that it is difficult to understand 

 why many investigators misinterpret the prementum as the "mentum" 

 in the Diptera. Furthermore, the prementum of the Diptera bears 



