1911] Muir and Kershaw — Mouth-parts of Uemiptera 7 



The orifice of the syringe tube opens through the base of the 

 labium, and is covered by a small chitinous tongue (pt), which lies 

 just beneath the hypopharynx. The plunger being retracted by the 

 muscles (spm) draws the saliva from the ducts (sd) into the syringe 

 barrel. On the relaxation of the muscles, the natural elasticity 

 of the plunger performs the return stroke, closing the valve (v) 

 and forcing the saliva past the tongue (pt) on the base of the 

 labium. 



The labium is four- jointed and sub-cylindrical in cross-section, 

 with a longitudinal groove running down its dorsal surface. 

 Beyond the distal end of the labrum-epipharynx (le) the edges of 

 the groove meet together, and so form a trough in which the 

 setse lie. Strong muscles between the dorsal and ventral walls of 

 the labium enable the edges of the trough to be parted so as to set 

 the setse free. The ventral wall (Fig. 13, vwl) is formed by very 

 thick chitin, perforated by numerous pores; the dorsal wall (divl) 

 is thin and flexible. Two large tracheae (tr), and two nerve-cords 

 (n) pass down to the tip of the rostrum. The rostrum is retracted 

 and drawn up to the underside of the head — into its normal 

 position at rest — ^by the retractor muscles (Fig. 11, rm) attached 

 to the greatly reduced first ventral sclerite (vhl*); it is extended 

 by the muscles (em) attached to the second dorsal sclerite. Longi- 

 tudinal muscles down the interior of the rostrum actuate the sev- 

 eral joints thereof; the last joint, or tip, is especially mobile, and 

 can be deflected laterally to either side. 



Almost on the mandibular suture (Fig. 10, ms), but slightly 

 below and at the posterior end thereof, the mandibles are con- 

 nected to the gense by a ginglymus articulation (Fig. 12, </ and 

 Fig. 10, art. man. s), consisting of a small rod and triangular plate, 

 the latter hinging directly to the gena. The protractor muscles 

 (p7n^) of the mandibles {man. s^., Figs. 12 and 14) attach to the 

 clypeal region between the bases of the antennae, and at the 

 other end at one arm of the triangular base of the mandible 

 (Fig. 14, tbm). A membranous sleeve (msl), arising from near 

 the articulation of the triangular base of the mandible, encloses 

 the mandibular seta, and forms the air-tight joint; at the anterior 

 end the sleeve (part of hypodermis) opens near the base of the 

 maxiUary plate. Behind the ginglymus the setse narrow to mere 



*This is the free part of basal labial joint; the rest is fused with gular region. 



