100 
Mo uthy arts of Pediculus 
The relationship of the structures surrounding the mouth, when the louse 
is not feeding, is best understood by reference to the accompanying illustra¬ 
tions. 
The “ haustellum,’' in PL YI, fig. 1, is shown slightly protruded from the 
thin chitinous diaphragm which forms the blunt front of the head. It is 
incompletely circular, the periphery being interrupted ventrally thus forming 
the buccal slit (Text-fig. I). The chitin of the haustellum is continuous with 
that which lines the entrance to the food canal. Anteriorly are “two dental 
;plates , which are everted in the figure and loosely hinged to the buccal 
plate” (Harrison). This is confirmed in my sagittal sections. From the base 
of the haustellum, on each side of the buccal slit and at the opening of the 
mouth, strong chitinous structures festoon posteriorly and laterally to the 
side of the clypeus; these may be called the buccal festoons. 
Fig. I. Pediculus humanus. Anterior portion of head in dorsal aspect showing the 
everted denticles. The stabbers omitted. 
The general scheme of the internal mechanism concerned in feeding may 
be understood by reference to Plate VI, fig. 1. The two main features are 
(1) the food canal and (2) the stabber-sac. The buccal region consists mainly 
of the buccal funnel (b.f.), it leads to the relatively large bladder-like pumping- 
pharynx (p.p.), which narrows greatly posteriorly, and opens into the muscular, 
bulbous pharynx (ph.), from which runs the simple tubular oesophagus ( oe .). 
The stabber-sac, which lodges the piercing mouth-parts or stabbers, is a ventral 
diverticulum arising anteriorly from the floor of the food canal and runs 
backwards as far as a diaphragm of tissue which partially separates head and 
thorax; it is supported posteriorly by a pair of large retractor muscles (p.s.rt.). 
Where the sac leaves the food canal two paired structures, with a certain 
amount of connective tissue, arise from the walls of the sac as half-tubes (s.t.) 
and run forwards in the buccal funnel as far as the buccal festoons ( b.fs .). 
The presence of this sac tube was not observed by Harrison who consequently 
