Undescribed Palpi, &c. By Walter Wesche, 413 



addition, immediately below the labrum a hollow lancet is always 

 found, the hypopharynx. 



In Empis, fewer parts are present, the mandibles being absent. 

 The labium has trachea?, and there are traces of rod-like chitinous 

 structures on the dorsal side, which are not seen in Kcemaiopota 

 pluvialis, fig. 3. 



In Syrphus, are identical parts. In the genus Syritta, the 

 maxilla? are ciliated at the tips with fine hairs, while the chitinous 

 rods on the dorsal side of the labium are strongly marked, fig. 4. 

 In both these families, as far as my observations go, the palpi are 

 attenuate, and situated lower down the proboscis than in the 

 Muscidae, well on the bases of the maxilla?. 



In Musca, still fewer parts are seen, both mandibles and 

 maxilla? having apparently disappeared. If we now compare 

 those labia which are tracheated with each other, after the soft 

 parts have been dissolved in caustic potash, we may formulate 

 the three following simple rules : — 



(1) In flies which have all the armature, with the exception of 

 the palpi, present, the labium has little or no chitinous structure 

 on the dorsal side. 



(2) In flies which have only the maxilla? present, chitinous 

 structures are visible on the dorsal side of the labium. 



(3) In flies which have both mandibles and maxilla? aborted, 

 the chitinous structure is equally, if not more marked than in the 

 second case. 



From these facts and by this " rough-and-ready " method we 

 may infer : — (1) That in the Muscida?, the mandibles and maxilla? 

 are soldered into the labium, and their rudiments may be seen as 

 the chitinous framework on the dorsal side. (2) That the maxillary 

 palpi are rudimentary or have disappeared, and that the palpi 

 always present and generally regarded as maxillary, are labial. 

 (3) That the proboscis is the true labium or lower lip, and that 

 the chitinous shield on the ventral side, the lower labial plate of 

 Kraepelin, is the mentum. 



In support of this nomenclature of the palpi, I give a figure 

 of the mouth-parts of Dilophus albipennis, which has the palpi 

 right down on the labella, and which seem undoubtedly labial, 

 fig. 9. This traverses the accepted dogma, that the labial palpi 

 are absent in Diptera. But a more convincing argument can be 

 found, in the discovery of several species with well marked palpi 

 on the levers that work the labrum and hypopharynx, and imme- 

 diately on the bases of the chitinous structures on the dorsal side 

 of the labium, in addition to the two always present. These must 

 be the maxillary palpi, and the higher palpi which spring from a 

 membrane and have no chitinous foundation, the labial. 



It may be argued, that if these were labial palpi, that is to 

 say, palpi on the lower lip, they would not be situated on the 



