1914] Tower—Mechanism of the Mouth Parts of the Squash Bug 101 
the maxille and their tips are barbed. Their function is 
that of piercing the plant tissues and holding the sete in 
place, while the tips of the maxillze, which are acute and fluted, 
probe the plant tissues, take up the plant juices and eject the 
saliva. 
At the point where the maxillary sete diverge they are sur- 
rounded by a membranous sheath, which renders air tight their 
connections with the pharynx (ph) and with the salivary pump 
canal or efferent canal (ec). After separating, the maxille together 
with the mandibles pass back, one of each on either side of the 
pharynx. The above mentioned membranous sheath also extends 
back on either side of the pharynx and encloses the set, being 
fastened to their bases. Soon after the maxillary and mandibular 
setz have separated, at their junction with the pharynx, the man- 
dibles separate from the maxille and take up a position above 
them. 
The bases of both the maxillze and mandibles widen posteriorly, 
forming attachments for the muscles which operate them, espe- 
cially the inner dorsal portion of the base of the maxille. This 
becomes thickened to form a prominent ridge to which the chitinous 
rod (h), see Pl. 1 f. 7 and Pl. 2 f. 9, which articulates with the gene, 
is fastened by a short tendon. The rod runs downward between 
the setz and the side of the pharynx, turning under the sete, 
and here lies above the tentorial lobes, being embedded in a mem- 
brane which separates the muscles of the setz from these lobes. 
Laterally the end of this crescent shaped rod is fastened to the 
under side of a small internal knob on the gene (p) situated 
directly below the compound eye. Ventrally the rod is attached 
to the tentorial lobe, see Pl. 1 f. 7. 
The maxillary sete are each controlled by two powerful muscles, 
both of which are attached directly to the bases of the maxille. 
These are the protractor muscle (pm), which extends anteriorly 
and is attached to the inside of the maxillary lamina and the side 
of the tentorial structure supporting the pharynx and salivary 
pump; and the retractor muscle which extends posteriorly and is 
attached to the occiput and also by a few fibres to the dorsal sur- 
face of the tentorial lobe. 
Each mandibular seta is controlled by two series of muscles. 
The two retractor muscles (rm), see Pl. 1 f. 3, are attached directly 
