MECHANISM OF SUCTION IN SCHIZONEURA LANIGERA. 313 



At the anterior end of. the pharynx the walls of the fold are composed of 

 very stout chitin and form two strong chitinous struts, the pliaryngeal struts 

 {pJi.st., figs. 13 & 14), which extend to the antero-lateral walls of that structure, 

 affording a firm support for it. The clypeal folds separate the clypeus from 

 two lateral sclerites, the clypeal sclerites, cl.sc. (mandibular sclerites or lorse 

 of some authors) . 



Two maxillary sclerites, mx.sc, are situated below the clypeal sclerites, and 

 help to form the latero-ventral walls of the fore-head. They extend ventrally 

 towards the mid-ventral line. In the post-ventral region they merge into 

 the floor of the fore-head which is composed of thin chitin, fig. IS, f.h. 



Distally, the maxillary sclerites lie close together in the mid-ventral line 

 and extend beneath the clypeo-labrum and labrum. They are separated for 

 some distance, however, by a median plate of chitin which merges proximally 

 into the ventral wall of the fore-head. This is the liypopliarynx, hyp. It is 

 continued forward beneath the pliaryngeal duet, pli.d., as a small liypopliarynx 

 lip, hypd., fig. 1. The maxillary sclerites, closely apposed in the median Hue, 

 extend beneath the hypopharynx lip, concealing it from the ventral aspect, 

 and form two tapering processes, the maxillary processes as seen in sections, 

 figs. 4-7, and shown in fig. 2, mxp. 



The maxillary sclerites turn inwards on each side of the hypopharynx and 

 form two deep folds, the buccal folds, h.f. These folds remain open through- 

 out and form two large cavities or chambers, the buccal cavity, b.c, which 

 accommodate the stylets. Towards the distal end, the internal faces of the 

 maxillary sclerites and maxillary processes are composed of stout chitin, and 

 ar grooved, thus affording support for the stylets, figs. 6-8. 



The hypopharynx lip extends beneath the pharyngeal duct, forming the 

 ventral wall of that structure. Proximally the lip dips down and becomes 

 continuous with the broader portion of the hypopharynx, hyp. A large bay 

 is thus formed in which the salivary pump, text-fig. 2, s.p., is situated, 

 being attached to the wall of the hypopharynx by means of a stout chitinous 

 supporting base, figs. 2, 12, 13, and 23, p.s. 



The salivary pump can be seen through the integument in cleared speci- 

 mens as a dark " y "-shaped chitinous structure. 



The floor of the fore-head, into which the hypopharynx merges at its 

 proximal end, becomes continuous with the dorsal wall of i\iQ 2yroboscis or 

 labium, fig. 1, Ibm., and text-fig. 2 (p. 325). This latter structure turns 

 beneath the hypopharynx, and at its proximal end its walls consist of thin, 

 flexible chitin. 



The post-lateral walls of the fore-head are composed of thinner chitin, 

 fio-. 18, l.w. When viewed from the anterior or dorsal face, in cleared 

 specimens, there appears to be a ridge of chitin running along the lateral 

 edges of the clypeus. This however, is due to the thick chitin of the clypeus 

 joining on to the thinner lateral walls of the fore-head. 



