OF SUCTION IN LYGUS PABULINUS., 719 
sclerite, the other passing below the pharynx. It seems that 
the latter pair does not represent the protractors but the pump 
muscles. 
Tur PHARYNX, on ScHLUNDKOPF. (Text-fig. 2.) 
This is one of the interesting and characteristic organs of the 
Rhynchota. In transverse sections it resembles roughly the 
pharynx of a sucking Dipterous insect (Nuttall and Shipley (40)). 
There are, no doubt, some differences in each case, but the general 
plan is the same throughout. In all these cases suction is effected 
by the production of a partial vacuum inside the pharynx, in 
order to fill which the sap or blood flows up the proboscis. 
The pharynx is a long, chitmous organ with a narrow 
lumen. Its structure varies in different regions of the head, and 
therefore it is proper to treat its several parts under different 
names, 
There are three distinct modifications in different regions :— 
(i.) The Pharyngeal duct, in the clypeal region, where the 
operculum as such does not exist, and the whole structure—here 
formed from the lower wall of the pharynx alone—forms one 
round duct which opens into the suction-canal. (Text-figs. 11-13, 
PhD») 
(ii.) The Pharynx proper, in the clypeal region and the anterior 
part of the epicranium, where its upper wall, as the operculum, is 
clearly distinguishable. (Text-figs. 14-21, Ph.) 
(ili.) The Csophagus, in the epicranial region, where the walls 
of the pharynx are soft, and the operculum as such disappears. 
(Text-figs. 2, 22, Cis.) 
(i.) Zhe Pharyngeal duct. 
This is the continuation of the pharynx proper into the labral 
region where it opens into the suction-canal. It is the modified 
pharynx, the modification consisting in a gradual elimination of 
the epipharynx from the upper wall of the pharyngeal duct, from 
behind forward. The lower wall at the same time gradually gets 
thinner and more rounded and ultimately forms a duct by itself. 
The divaricator muscles of the pharynx have disappeared with the 
operculum. At the place where the pharynx ends and the duct 
begins there are found the gustatory organs communicating with 
the lumen of the duct through the ecribriform plate (text fig. 26, 
G.Or., Cri.P].) In this region the hypopharynx (text-figs. 13, 14, 
Hyp.) is well developed, forming a folded structure supporting 
the maxillary stylets and the mandibles laterally, and enclosing 
the efferent salivary duct underneath. It supports the pharyngeal 
duct in the region where it has no other support, neither that 
of the body of the tentorium nor that of the tentorial arms. 
Anteriorly the hypopharynx becomes smaller and smaller and less 
folded. It brings the efferent salivary and the pharyngeal ducts 
nearer to each other (text-figs. 11-13, Ph.D., E.S.D.), and finally 
