A. J. Grove 
469 
and it is possible that the slightest reduction of pressure within the pump 
chamber, would release any closing effect exercised upon the afferent duct, 
and the secretion would be poured into the chamber simultaneously with the 
raising of the chitinous membrane. This would preclude the possibility of 
extraneous fluid entering the chamber by the efferent duct. 
The Pharynx. 
The pharynx in P. mali presents no unusual features, and is constructed, 
as in so many Hemiptera, to perform a suctorial function. It varies in the 
shape of its cross section as it is traced from the point where it curves over the 
transverse bar, down towards the oral region. The posterior wall is more 
strongly chitinised than the anterior one, and in the upper portion is semi¬ 
circular in outline, the thinner anterior wall forming the diameter of the semi¬ 
circle. As the mouth is approached, the posterior wall assumes a more and 
more V-shaped form, and also becomes progressively more strongly chitinised. 
In this region the anterior wall also becomes V-shaped, but still remains thinner 
and lies inside the larger V of the posterior wall, so that the extremities of the 
arms of the two Vs are joined together. The pharyngeal muscles are attached 
to the inner side of the base of this smaller V, and the suctorial effect is pro¬ 
duced by a reduction of pressure within the pharynx, following upon the 
raising of this thinner wall or operculum by the contraction of these muscles. 
THE MUSCULATURE OF THE HEAD. 
In discussing the musculature of the head, it will be convenient to consider 
the muscles in groups in accordance with the portions of the head or append¬ 
ages with which they are associated. The number of muscles concerned is 
large, considering the size of the parts, and to give separate names—many of 
which would have to be invented—to each, would be too cumbrous and lead 
to confusion. The system will therefore be adopted of indicating the various 
muscles in each group by numbers. 
I. The Antennal Muscles. 
The movements of each antenna are controlled by a set of five muscles 
which are attached around the base of the appendage where it articulates with 
the head capsule, and stretch from thence to the dorsal surface of the anterior 
support of the tentorium of its side. The muscles vary in size and consist of 
two large muscles, two small ones, and one very slender one. 
II. The Pharyngeal Muscles (PI. XXVI, figs. 2 -4). 
These muscles, by the operation of which the pumping action of the 
pharynx is effected, consist of a series of muscles arranged in pairs one above 
another, and are attached at one end to the centre of the lower portion of the 
operculum of the pharynx, and at the other to the inner side of the clypeus. 
