Ture Hoa Louse 681 
by the two pairs of protractor muscles. Sikora’s second suggestion is 
based on the fact that she (1916:18) regards the basal part of the ‘‘ man- 
dibles” of Enderlein as the posterior articular processes of the true 
mandibles, which Enderlein (1995:637) in turn has interpreted as the 
ventral prolongations of the lateral sclerite. According to Enderlein 
these are pushed far under the scalelike labium and are covered by it 
ventrally. Sikora attributes the double function of opening the mandibles 
and moving forward the pharynx to the ventral protractor muscles, and 
their closing to the contraction of the tendon muscle. No constructive 
criticism of this interpretation is offered for the present, because it is 
believed that the final morphology of the parts can be determined only 
by embryological investigation. : 
The mouth parts 
From the ventral surface of the stomodaeum at the junction of the 
buccal plate and pumping pharynx a diverticulum is given off. It passes 
backward under the alimentary canal to the extreme posterior end of 
the head, which is separated from the thorax by a thin, ‘structureless, 
cuticular membrane, staining pink in hematoxylin and eosin preparations. 
Within this diverticulum lie the piercers and the salivary duct. The 
piercers (Plate LX, 7 and 8) consist of dorsal and ventral elements, and 
their total length is approximately 1.2 millimeters. The ventral element 
is made up of two parts, a dorsal and a ventral, which are very closely 
apposed to each other throughout the greater part of their length. 
The sheath 
The wall of the sheath is continuous with that of the stomodaeum and 
consists of somewhat flattened epithelial cells lined by a fine chitinous 
intima (Plate LXI, 7). On its inner surface next the coelom the sheath 
is also covered by a fine chitinous cuticula, the origin of which is discussed 
later. Its dorsal and lateral walls are of uniform thickness and appearance, 
while on the ventral wall there is imbedded a chitinous plate. This 
plate occupies approximately the posterior two-thirds of the floor of the 
sheath and is separated from the anterior third by a transverse suture. 
A similar condition has been described by Harrison (1916b:209) in the 
body louse. In this region of the plate there is a central groove in the 
