64 MEDICAL ENTOMOLOGY 



apodemes are long and stout, and terminate at the proximal end in 

 rounded points. 



The hypopharynx is a very slender flattened organ, of the type seen 

 in the Stomoxydinae, and contains the salivary duct between its two 

 layers. At the upper end of the haustellum the flattened lateral areas 

 are absorbed ; the dorsal lamina fuses with the closed part of the 

 epipharynx, the ventral with the labial gutter, while the salivary duct 

 passes into a deep pocket-like recess in the middle of the latter. 



The wall of the labium is composed of the mentum and the labial 

 gutter, which serve about equally in rendering the proboscis a rigid 

 piercing organ. The mentum in the bulb is composed of rather thin 

 chitin, and is devoid of hairs. In the narrow part it is very thick 

 and strong, and forms a shallow trough occupied mainly by a 

 pair of tendons and some muscle fibres connecting it with the gutter. 

 On its external surface there are two parallel rows of minute spines 

 extending from the labellar area to the bulb ; the hairs are arranged in 

 pairs, the intervals between which diminish progressively as the bulb is 

 approached. The labial gutter is a shallow trough of thick chitin, of 

 almost as great a breadth as the mentum, to which it is connected by a 

 narrow band of thick fibrous tissue. At the sides there is a ridge of chi- 

 tin projecting downwards and slightly outwards, in line with the 

 lateral margins, so as to give the gutter on section the appearance of 

 a letter H, greatly elongated in the transverse diameter. The gutter 

 is not depressed between the sides of the mentum, nor does it extend 

 sufficiently far forwards to enclose the labrum-epipharynx. It is con- 

 tinued unchanged throughout the labellar region, but is slightly dilated at 

 the distal end for the reception of the bases of the teeth. 



The cutting apparatus consists of a set of teeth at the prestomum, 



corresponding to the prestomal teeth in the Muscidae, a serrated ridge 



on the external surface of the labellum on each side, 



itmg apparatus an( j & modification of the external wall which renders 



Of Hippobosca 



the distal portion capable of movement on the rest of 



the mentum. (Plate XIII, fig. 5.) 



There are five prestomal teeth on each side, arranged in a radiate man- 

 ner, the middle and largest tooth being directed straight forwards. 

 Its distal end is bifid, with two equal arms, while in the teeth on either 

 side of it the arm next the middle line is the largest. The proximal ends 

 of the teeth are rounded, and are fitted into the dilated end of the labial 

 gutter. The external set of teeth (Plate XIII, figs. 4 and 5) are flattened 

 and typically serrate, with points directed upwards towards the head. 



