LABEUM, HYrOPHAEYNX, . AND LABIUM. 107 



The Jahrum (Fig. 2, a) is somewhat shorter than the labium, 

 reaching to a point situated at the beginning of the distal ninth 

 part of the last-named oi:gan. It is naiTOW, though a little 

 broader towards the base ; in the natui'al condition the lateral 

 margins can be seen to turn downwards, and even a little 

 inwards, so that the labrum forms about two-thirds of a tube 

 (compare the diagrammatic transverse section. Fig. 6); the 

 lateral walls are flexible, the dorsal wall is a little thicker. In 

 Fig. 3 the labrum is shown from below and rather flattened ; the 

 median part (p), of a darker tint in the iigure, is the median 

 portion of the wall of the concavity on the lower side — the. 

 so-called epipharyngeal plate — which is moderately thick ; no 

 muscle is found in the cavity between this plate and the dorsal 

 wall. Fig. 4 shows that this thickening in the lower wall 

 terminates before the distal end of the labrum, which is in the 

 shape of a triangular and rather feebly chitinised plate. In 

 Fig. 5, the basal part is seen from below ; the lateral margins (m) 

 are bent a little inwards ; the small rings (s) are apertures in 

 the epipharyngeal plate (p), and from each aperture proceeds a 

 hair which is exceedingly tine (so much so that it was impossible 

 to show it in the flgure) and proportionately long ; somewhat 

 similar structures ha\ie been discovered in other Diptera, and 

 considered as organs of taste (compare the Jabrum of Stomoxys). 

 On the basal part these structures are numerous, but on the 

 remainder of the labrum there are very few of them (two are 

 shown in Fig. 4). The imier processes (Fig. 2, i) from the base 

 of the labrum, and the muscles to its base and to the pi'ocesses, 

 are as in Stomoxi/s (see below). 



The hypopharynx (Fig. 2, i';) is somewhat longer than the 

 labrum, and a little shorter than the labium, reaching slightly 

 beyond the base of the labella. As is usually the case in Diptera, 

 it is an exceedingly slender cylindrical tube,- being .the outlet 

 from the thoracic salivary glands ; its distal extremity ■ is mem- 

 branous (Fig. 7). 



The labium (Fig. 2, c, and Fig. 12, e) is very interesting. 

 The basal fourth is thick and inflated, considerably broader than 

 deep, with a median, rather broad dorsal groove ; its distal 

 three-fourths are very slender, nearly equal in depth throughout, 

 and somewhat compressed. This slender part has a very deep 

 median dorsal groove ; in reality it is strongly depressed, and the 

 V)road lateral thin parts are bent upwards and a little inwards 

 abovcjthusforming the groove between them, or, more correctly, 



