rARACOROTOCA AKKiafANI (waHJJKN). 333 



somewhat extoiuled, trougli-like labium. Tlie pliarnyx is a 

 vertical, iiarroAv tube with a relatively thick, cuticle layer 

 continuous with the exoskeleton. The lumen of the pharynx 

 is circular in cross-section, and no distinct hypopharynx or 

 clearly-defined epipharynx are developed. At some little 

 distance up the pharynx there is a slight ridge on each side 

 bearing short setee. Possibly these are gustatory in character, 

 and the two ridges may represent the remnant of an epipharynx 

 (PI. XVII, fig. 24a, g. ri.). The inner surface of the labium 

 is provided with numerous close-set short set^e (fig. 24a). 



Although cai-efully searched for no typical salivary glands 

 opening into the gut could be found. 



Sucking Pharynx. — The vertical, narrow pharynx opens 

 into a dilatation in the middle of the head. This is provided 

 with a well-developed system of muscles consisting of strong, 

 striated muscle-fibres. The nmsculature comprises longi- 

 tudinal fibres in contact with the sac and clumps of radial 

 fibres extending to the wall of the head-capsule and internal 

 skeleton. There appear to be six more or less distinct 

 clumps: a fronto-dorsal, a fronto-ventral, a pair of dorsal 

 and a pair of lateral. This muscular system is strikingly 

 similar to that of the sucking pharynx of a butterfly, and 

 here we have a convergence of structure probably arising 

 through the circumstance that the methods of solving the 

 mechanical problem are necessarily limited by the organisa- 

 tion of the head of an insect. The sucking pharynx is lined 

 by a. cuticle continuous with that of the narrow pharynx. 

 From Triigardh's description it is clear that the muscles of 

 the pharynx in Termitomimus are closely similar. 



CEsophagus. — From the posterior wall of the sucking 

 pharynx the oesophagus arises as an exceedingly narrow tube 

 which is closely surrounded by the cephalic nervous system. 

 On passing into the thorax it gradually dilates until it opens 

 into the mesenteron in the hinder region of the metathorax. 

 There is no suggestion of a crop and no gizzard nor pro- 

 ventriculus. The oesophageal wall is provided with a well- 

 developed muscle layer (PI. XIX, fig. 58, m. c), a very thin 



