320 ME. J. DAVIDSON ON THE MOUTH-PARTS AND 



H. Musculature of the Salivary Pump. 



The structure o£ the salivary pump is such that it acts as a force-pump, 

 the working o£ which is controlled by the large spindle-shaped pump-muscle 

 shown in fig. 1 and fig. 2, p.m. 



The pump-muscle is attached to the flexible, proximal wall of the cylinder 

 and extends beneath the pharynx, towards the transverse plate of the ten- 

 torium, being partly attached to the latter structure and partly to the stout 

 ventral wall of the pharynx. It is divided for some distance along its 

 length, as is seen in transverse sections. The musculature will be considered 

 in more detail later. 



I. TJlc Stylets. 



The stylets are situated below the pharynx, and consist of two anterior 

 or dorsal stylets, the mandihles {m.d., fig. 3), and two posterior or ventral 

 stylets, the maxillary stylets (mx.s., fig. 2). 



They are withdrawn for some distance into the fore-head, being swollen 

 in a club-shaped manner at their proximal ends. Distally they become 

 considerably reduced in size, and form long, needle-like structures which, 

 passing through the buccal cavity, extend along the longitudinal proboscis 

 groove. They are finely pointed at their distal extremities, vide fig. 24. 



The stylets are hollow chitinous structures, which are continuous with the 

 integument of the posterior end of the buccal cavity, being drawn inwards 

 somewhat after the manner of an inverted finger of a glove, i^ide fig. 23. 

 The cavity of the stylet-shaft is especially large in the swollen, proximal 

 part. From the proximal end of each emerges the retort-shaped organ 

 indicated in the series of transverse sections, md.o., mx.o. 



The relation of the stylets to other structures in the fore-head will be best 

 understood from the serial sections, figs. 4-18. 



The maxillary stylets. 



The maxillary stylets lie ventral to the mandibles, one on each side of the 

 median line, and are situated further back. As they emerge into the buccal 

 cavity they approximate towards each other, becoming considerably reduced 

 in size. As is seen in fig. 23, the integument of tlie buccal cavity, which in 

 this region is thin and membranous, is continued proximally along the shaft 

 of the stylets, forming a sheath in which those structures are freely 

 moveable. 



As the maxillary stylets enter the buccal cavity they lie one on each side, 

 along the internal lateral walls of the hypopharynx (fig. 15), fitting into 

 a longitudinally running bay or groove. 



