THE EPIPHARYNX 45 



an extension of the epipharynx, building up the dorsal end of the 

 labrum, this term is a convenient one to use. 



In the lower orders of truly mandibulate insects, from the Thysan- 

 ura to the Coleoptera, excluding those which suck in liquid food, 

 such as the Diptera, Lepidoptera, and Hymenoptera, and the 

 Mecoptera (Panorpidae) with their elongated head and feeble, small 

 mandibles, the epipharynx forms a simple membranous palatal lin- 

 ing of the clypeus and labrum. In such insects there is no soft pro- 

 jecting or pendant portion, fitted to close the throat or to complete 

 a partially tubular arrangement of the first and second maxillae. 



In all the mandibulate insects, then, the epipharynx forms simply 

 the under surface or pharyngeal lining of the clypeus and labrum, 

 the surface being uniformly moderately convex, and corresponding 

 in extent to that of the clypeus and labrum, posteriorly merging into 

 the palatal wall of the pharynx ; the armature of peculiar gathering- 

 hairs sometimes spreading over its base, being continuous with those 

 lining the mouth and beginning of the oesophagus. The suture 

 separating the labrum from the clypeus does not involve the epi- 

 pharynx, though since certain gustatory fields lie under the front 

 edge of the clypeus, as well as labrum, one may in describing them 

 refer to certain fields or groups of cups or pits as occupying a labral 

 or clypeal region or position. 



The lack of traces of a suture in the epipharynx corresponding to 

 the labral suture above, suggests that the labrum does not represent 

 a pair of coalesced appendages, and that it, with the clypeus, simply 

 forms the solid cuticular roof of the mouth. 



The only soft structures seen between the epipharynx and labrum, 

 besides the nerves of special sense, are the elevator muscles of the 

 labrum, and two tracheae, one on each side. 



The structure and armature of the epipharyngeal surface even 

 besides the taste-pits, taste-cups and rods, is very varied, the setae 

 assuming very different shapes. There seem to be two primary 

 forms of setae, (1) the normal forms which arise from a definite cell ; 

 and (2) soft, flattened, often hooked hairs which are cylindrical 

 towards the end, but arise from a broad triangular base, without 

 any cell-wall. These are like the " gathering hairs " of Cheshire, 

 situated on the bees' and wasps' tongue ; they also line the walls of 

 the pharynx and extend toward the oesophagus. They are also 

 similar to the " hooked hairs " of Will. The first kind, or normal 

 setae, are either simply defensive, often guarding the sense-cups or 

 sensory fields on which the sense-cups are situated, or they have a 

 nerve extending to them and are simply tactile in function. 



