OF SUCTION IN LYGUS PABULINUS. 725 
The pump may conveniently be divided into four parts for 
description :— 
(i.) The pump-cylinder with the pump-chamber and the 
Bre ae) (Wexp-test 2.03 (7) [4015216 POys 
-UD., £ OU.) 
(ii.) The piston with the handle. (Text-figs. 15,16; Pi., 
lei dls)) 
(iii.) The efferent salivary duct. (Text-figs. 3, 10-15, E.S.D.) 
(iv.) The afferent salivary duct. (Text-figs. 2, 3, 16, ete. 
A.S.D.) 
(i.) The pump-ceylinder with the pump-chamber and the pump- 
stem.—The pump-chamber is more or less oval in section, and its 
thick and rigid chitinous lining (constituting the pump-cylinder) 
consists of two walls, an anterior and a posterior, which differ 
from one another in structure and shape, though there is no 
discontinuity of chitin between them. 
(a) The anterior wall (A.W.P.). This is roughly semicircular 
in section. Its middle portion is drawn out anteriorly into a 
thickened solid process, which fuses with the hypopharynx, and 
this thick portion of the pump is known as the pump-stem (text- 
fig. 3, P.St.), which is perforated by the efferent salivary duct. The 
chitin of the anterior wall is thick, elastic, and incompressible. 
It gets, however, thinner laterally, and is continued into the 
posterior wall dorsally; but ventrally it lines the entrance of 
the afferent salivary duct. 
(6) The posterior wall. This is apposed to the anterior wall in 
the normal position. Its middle portion is swollen and is called 
the piston. This is continued backward to form the handle. 
Its chitinous lining is elastic, introversible, and can be retracted 
from the anterior wall to a certain extent when the pump 
muscles act. These muscles have already been described above. 
(c) The pump-chamber. The space between the walls, anterior 
and posterior, of the pump-cylinder constitutes the pump-chamber, 
In the normal position, when the posterior wall is apposed to the 
anterior, its capacity is reduced to a minimum. JIntroversion, of 
course, increases this capacity. Into the chamber opens antero- 
ventrally the afferent salivary duct, and from it issues antero- 
dorsally the efferent salivary duct, which latter finds its way out 
through the pump-stem to open into the ejection-canal of the 
maxille. (Text-figs. 3, 10 B., P.Ch.) 
(d) Attachment. The pump-cylinder is attached by connec- 
tive tissue to the body of the tentorium, which is situated just 
above it; the ventral groove of the tentorium corresponds 
exactly to the dorsal semicircular contour of the pump-cylinder. 
The attachment of the cylinder to the hypopharynx through the 
pump-stem has already been mentioned under (a). 
(ii.) The piston with the handle.—The middle portion of the 
posterior wall is swollen and continued backward to a considerable 
