^} Introduction. 



witli 110 oral cone it send?, at its lower end, a pair of small processes 

 forwards to tlie, iii Hiis case not separated, clypeus or it is at all events 

 in some connection with it; wlien on Ihe contrary an oral cone is 

 present, tliese processes generally are large and strongly connected 

 with the clypeus. Between these processes, stretching from the anterior 

 wall of the pharynx to the clypeus, or in flies without an oral cone, 

 to the clypeus and epistoma. lie the muscles which aet as pumping 

 muscles during the sucking. On account of the connection ot the 

 clypeus with the pharynx, the clypeus has sometimes been considered 

 as a part of the pharynx, and pharynx together with clypeus has 

 been termed fulcrum by Menzbier (Ueber das Kopfskelet und die Mund- 

 werkzeuge der Zweifliigler, Bull. d. la Soc. imp. des nat. de Moscou. 

 IV, 1880), and „Schlundgerusf by Becker (Zur Kennln. der Mund- 

 theile der Dipteren, Denkschr. d. niath. nat. Classe d. Kais. Akad. d. 

 Wissenscli., Wien, XLV, 1882). In reality it is only a chitinised part 

 of the dermis, connected with the lateral wings of the pharynx, and 

 answering to the clypeus in other orders. It has also been termed 

 prælabrum. When an oral cone is developed the proboscis is highly 

 pro- and retractile, the membraneous cone being folded in, or moro 

 strictly speaking, it is laid up backwards in the aperture, the connection 

 between clypeus and epistoma acting as a hinge. The real oral 

 aperture is naturally at the lower end of the oral cone, but it may 

 be convenienl to term the chitini-sed edge of the under side of the 

 head to which the cone is attached, the mouth-edge, and speak of 

 the aperture surrounded by this edge as the moulli-aperture. 



WMi regard to the antennæ I generally count as niany joints as are 

 really present, so that I f. inst. count a two-jointed style or arista as 

 two antennal joints, only using the terms complex, style and arista 

 as merely descriptive; I expressty mention this partly because Wandolleck 

 in a paper (Ueber die Fiihlerformen d. Dipt., Zool. Jahrb., Abtheil. 

 fiir Syst. VIII, 1895) seems to be of the o])inion that dipterologists 

 have not considered the actual number of the antennal joints what I 

 still think scientific dipterologists have done in the last lialf century. 

 but the terms mentioned are convenient in descriptions. 



As to the thorax I use for the sterna and pleura tlie terms pro- 

 posed by Osten Sacken (An Essay of comp. Chætotaxy, Transact. Ent. 

 Soc. London, 1884); the terms are (fig. 1) a, mesopleura, b, pteropleura, 

 c, sternopleura, d, hypopleura, e. metapleura. The terms are very con- 

 venient, I therefore usethem; only the term metajiloura is in so far 

 inadæquate as I take this part as belonging to the mesothorax. but 

 yet the term may be used. The part below or behind scutellum 

 is termed the postscutellum . generally it is more or less vertical. l)nt 



