318 MR. J. DAVIDSON ON THE MOUTH-PARTS AND 



I have given a longitudinal section, fig. 25, through the epipharynx, 

 showing the position and structure, so far as I am able at present, of this 

 gustatory organ. The section is not quite median, so that the surrounding 

 chitinous structures are not shown very clearly. 



F. Musculature of the Pharynx. 



The anterior or dorsal wall of the pharynx is acted upon by powerful 

 bands of divaricator muscles, which pull out this flexible dorsal wall, thus 

 greatly increasing the lumen of that structure. In the distal half of the 

 pharynx an upright membrane or tendon, m.t., is attached along the middle 

 of the pharynx-wall, and to this tendon are attached the divaricator muscles, 

 d.m., as is shown in figs. 12-16. The muscles pass from each side of this 

 median tendon in parallel bands, and become attached to the wall of the 

 clypeus, on each side of the median line. The internal face of the clypeus 

 possesses several, small, projecting ridges of chitin, which afford a firm 

 attachment for the muscles. These muscles extend to the clypeus in a 

 slightly posterior direction^ so that in transverse sections they are often cut 

 across, as shown in fig. 17. 



The muscles attached to the proximal end of the dorsal wall of the pharynx 

 are smaller. They converge towards the post-dorsal wall of the clypeus, 

 becoming inserted on its internal face, near together, on each side of the 

 median line. 



In fig. 1, which is a slightly scheniiitized median, longitudinal section 

 through the head, the muscles are cut through obliquely and pass out of 

 the line of section before reaching the clypeus. 



Between the pharynx protuberances, the pharynx is narrow in transverse 

 section, figs. 12 and 13, and " U "-shaped. When the divaricator muscles 

 are relaxed, the flexible dorsal wall becomes closely ad{)ressed against the 

 ventral wall, completely closing the lumen. 



G. The Salivary Pump. 



The salivary pump is a bell-shaped chitinous structure situated below the 

 anterior end of the pharynx, being attached to the hypopharynx, vide fig. 2. 



In longitudinal section, vide fig. 1, it is seen to consist of a stout chitinous 

 distal portion, forming the handle of the bell. This is the pump-stem, p. s. 

 It widens out at its proximal end to form a cup-shaped portion — the body of 

 the bell — which is the pump-cylinder, p>.c. These parts are [)erhaps better 

 shown in vertical section, fig. 23. 



"Ihe pump -cylinder is a thick- walled, cup-like structure, composed of thick 

 chitin which encloses the pumjj-chamher, p>.ck. 



The proximal wall of the cylinder consists of membranous chitin, which is 

 continuous with the thick rim of the cup. This wall is usually seen with- 

 drawn into the cylinder, so that only a small part of the chamber remains 

 showing. Attached to this proximal wall is a small club-like tendon to 



