720 MR. P. R. AWATI ON THE MECHANISM 
disappears, leaving free these ducts, which open ultimately into 
the suction- and the ejection-canals respectively (text-figs. 10 A 
and 10 B). 
The pharyngeal duct runs to a considerable distance into the 
suction-canal before it ends, The importance of this arrangement 
lies in the fact that it makes allowance for the movements—-up and 
down—of the maxillary stylets. Had this duct run to a shorter 
distance into the suction-canal, there would have been some 
danger of its slipping out when the stylets were pushed down 
to their natural limit of extension. 
(ii.) The Pharynx proper. 
This is found to begin in the clypeal region behind the clypeal 
folds and to end in the anterior part of the epicranium, It is 
bent anteriorly, and its bend corresponds to that of the head. 
Posteriorly it is straight and runs directly into the csaphagus, 
It is different in structure from the pharyngeal duct and from 
the esophagus. It is the chief organ of suction in the insect. 
When seen in transverse section it consists of two distinct parts : 
the ventral part and the dorsal, The first may be called the “ V ” 
and the second the operculum. ‘They are different in shape and 
structure. (Text-figs. 14-21.) 
(a) The “V” or ventral wall of the pharynx (V.Ph.).—This is 
more or less V-shaped in section, its angle being considerably 
drawn out in some places. In the anterior and the posterior 
regions this angle gets rounder, and the characteristic form of the 
“V" is lost, as in the pharyngeal duct and the esophagus. In 
the clypeal region, where the pharynx proper begins, the arms of 
the “ V” are elongated and fused with the clypeal folds running 
into the head (text-figs. 16, 17, 19, Clp.F.). Thus it is dorsally 
supported by these folds. 
In the same region, moreover, the ‘‘ V” is wedged ventrally 
into the body of the tentorium and retained there by the connec- 
tive tissue, its ventral shape corresponding exactly to the dorsal 
groove in the latter (text-figs. 17, 19, T.B., V.Ph.). The dorsal 
arms of the tentorium run parallel with those of the ‘*V” and 
support it laterally. It is this part of the pharynx which needs 
support because it is here that the sucking force is applied, 
The posterior arms of the tentorium as they run backward 
also support the pharynx to some extent, but they soon diverge 
laterally and leave it (text-fig. 20, P.A.). 
The “ V ” is of thick chitin which, however, becomes thin and 
soft anteriorly and posteriorly in the pharyngeal duct and the 
cesophagus. 
(b) Lhe Operculum or dorsal wall of the pharynx (Op.).—Its 
structure is entirely different from that of the “V”. It is closely 
apposed to the “V” in its normal position, which is regained 
by its own elasticity, and from which it is pulled by contraction 
of the divaricator (pharyngeal) muscles. It is obvious that there 
