63 



is almost entirely composed of a thick membrane, there being only a 

 small elongate area in the middle line which is strongly chitinized ; 

 the main mass of the dilator muscles of the pharynx are inserted into 

 this median area. 



The buccal cavity in this form has the shape of a long chitinous 

 tube, which connects the pharynx with the food canal in the haustel- 

 lum. The lateral walls of the tube are much thicker than the dorsal 

 and ventral walls, and project outwards and backwards in the distal 

 portion of the tube so as to form a shallow groove for the reception 

 of the salivary duct. The lumen of the tube is of uniform diameter 

 throughout, and is circular, though a little narrower in the. dorsal than 

 in the ventral half. (Plate XIII, fig. 2.) At the upper end of the buc- 

 cal cavity its walls are continuous with those of the pharynx, while 

 at the distal end the union with the food canal in the haustellum is 

 brought about in a manner similar to that of Musca ; the cavity is 

 slightly dilated, and encloses the end of the food canal, which is here 

 a closed tube. The edges are united by a short membrane, so that 

 although the continuity of the tube is maintained, free movement is 

 possible. 



The haustellum strongly resembles that of Glossina. The bulb oc- 

 cupies only the upper third ; the narrow part distal to this is curved 

 downwards and forwards, and terminates in a cutting apparatus much 

 simpler than that of the Muscidae. The end of the labium is not clearly 

 divided into two labella, but the structures which make up the biting 

 apparatus are bilaterally arranged. 



The labrum-epipharynx is a relatively strong organ, shaped like a 

 long and narrow arrow-head, and rounded on the dorsal surface. (Plate 

 XIII, fig. 1.) It is not enclosed by the labial gutter, but forms 

 the dorsal aspect of the haustellum, and is beset with two parallel 

 rows of minute spines. The labrum and epipharynx are closely fused 

 together in the distal part of the proboscis, but separate higher up ; 

 the distal end of the labrum is fused with a membrane correspond- 

 ing to the anterior surface of the rostrum, while the epipharynx forms a 

 closed tube by the union of its sides, and unites with the buccal 

 cavity as already described. On the external surface of the sides of 

 the labrum there is a row of short spines, where it is pressed against 

 the labial gutter. At the distal end the labrum broadens out consider- 

 ably, and is produced into two tubercles, which are fitted into corre- 

 sponding shallow pits on the distal ends of the labral apodemes, this 

 being the reverse of the method of union in the Muscidae. The 



