1911] Muir and Kershaw — Mouth-parts of Hemiptera 5 



found in the Thysanoptera, where the maxillae form long, sub- 

 triangular plates which, together with the labrum, form a short 

 tube through which the setae pass. The paired setse are mandibu- 

 lar, and the unpaired seta pertains to the left maxillary, the 

 right being absent.^ An analogy, if not homology, is to be found 

 among the Myriapods in the family Polyzoniidse^, where the mouth 

 is adapted for sucking. Here the upper lip is produced into a 

 narrow snout, the lateral edges being turned down to form a 

 semi-tube; the protomalse are drawn out anteriorly into long 

 slender setae, with slightly spoon-shaped tips, set round its edges 

 with fine teeth, the basal part being stouter, somewhat triangular, 

 and articulated in the normal position (viz., near the base of the 

 dentomalae). The dentomalae form a thin plate, rounded at its 

 base, and drawn out thin anteriorly, which fits exactly against 

 the edges of the elongated upper lip, entirely covering the protom- 

 alae, thus making them internal organs. 



PART II. The Mechanism of the Mouth-parts. 



The membranous oesophagus (Figs. 11 & 12 oe) passes between 

 the brain (br) and the sub-oesophagal ganglion (sg), and then 

 merges in the chitinous pharynx (ph). The pharynx is. of the 

 usual double U-shape in transverse section, the dorsal plate being 

 thin and flexible, and capable of retraction from the thick and 

 chitinous ventral plate by the powerful pharyngeal muscles 

 {phm), thus creating a vacuum into which the liquid food flows; 

 the dorsal plate then falls back against the ventral plate by the 

 natural elasticity of the pharynx. The whole structure consti- 

 tutes the pharyngeal pump. The anterior portion of the dorsal 

 plate {dph) of the pharynx continues along the under side of the 

 labrum (le) and forms the epipharynx {e). The ventral plate of 

 the pharynx {vph) continues forward and forms the spoon-shaped 

 and acute hypopharynx {hyp). At the anterior end of the pharynx 

 the lateral edges of the ventral plate emit two struts {st), one 

 each side, which diverge laterally and upwards, and fuse with 

 the anterior sides of the clypeal region {clr) . These struts form the 



2See Note A. 



'The description of this mouth is taken from a species very common in rotten wood in the 

 Island of Ceram, 



