118 Mouthparts of Pediculus 
and position the buccal teeth merely appear to serve as anchors, but as 
Harrison suggests they may help to stretch the skin of the host. The saliva, 
which is probably injected at the deepest part of the wound, may serve as 
an irritant to stimulate haemorrhage from the capillaries or as an agent for 
preventing the coagulation of blood in the interior of the insect 1 . 
From the nature of their cells and the course of the secretion along the 
floor grooves to the sac tube, it would appear, on the other hand, that 
Pawlowsky’s glands produce a lubricant for the stabbers. 
By the pumping action of the pharynx, already explained, the blood is 
sucked up the afferent channel and passed into the alimentary canal. An¬ 
teriorly this afferent channel is possibly made up of the half-tubes of the 
pumping-pharyngeal tube and the buccal arch and, posteriorly, of the pumping- 
pharyngeal tube alone. 
When feeding is finished the various organs are withdrawn by their re¬ 
tractor muscles. 
CONCLUSIONS. 
It will be of interest to see what interpretations and homologies will be 
based on the foregoing description of the mouth-parts. It is hoped that the 
description will be of use to investigators who wish to ascertain through 
which channel the organisms of disease may find passage on the way from 
the insect to man. 
REFERENCES 
Harrison (1916), Martin (1913) and Peacock (1916), see Bibliography in Parasitology, 
x. pp. 1-421. 
EXPLANATION OF PLATE VI. 
PEDICULUS HU MAN US. STRUCTURE OF THE HEAD. 
Fig. 1. Tlie diagram represents a dissection of the right half of the head. Only the right half of 
the following structures in the mid-dorsal plane are shown—the buccal funnel, the food canal, 
the stabber-sac with the two stabbers, and the nerve ganglia. For clearness the structures 
of the stabber-sac, particularly those of the posterior end, are slightly displaced and distorted. 
Food canal (beginning anteriorly on first line), h. haustellum; d. denticles; d.pl. dental 
plate hinged to b.f. buccal funnel; b.fs. buccal festoons; ph.t. pharyngeal tube; f.t. fibrous 
tissue supporting buccal funnel; b.pr. dorsal protractor muscle of the buccal funnel; m.d-pr. 
four medial dilator-protractor muscles of the pumping-pharynx; d-l.d. three dorso-lateral 
dilators of the pumping-pharynx; pp. pumping-pharynx with setae; d.r. dorsal retractor 
muscle of the pumping-pharynx; pli. pharynx; sph. three sphincter muscles of the pharynx; 
dil. three dilator muscles of the pumping-pharynx. On the second line— pp.rt. posterior 
retractor of the pumping-pharynx; p-l.d. postero-lateral dilator of the pharynx; b.fs. buccal 
festoons. 
Stabber-sac (beginning anteriorly on second line), s.t. sac tube; d.s.t. dorsal stabber 
running beneath post-dorsal arch of sac tube; st.c. stabber-sac; d.st.t. tissue of dorsal stabber 
1 See in this connection Nuttall’s description of the feeding habits, Parasitology, x. 171, and 
the demonstration by him [Ibid. p. 74) that the salivary glands contain anti-coagulins. 
