1912] Stomoxys Calcitrans Linn. 425 
somewhat longer than the height of the head, distinctly thick- 
ened, in the basal half, black, shining, and practically smooth. 
The Jabium, or lower lip, is the strong black part referred 
to, and this constitutes the sheath for the labrum and hypo- 
pharynx. The labium consists of three segments. (Plate 
XXXIV, Fig. 1, 2, 2, 22). Segment 7 is eight to ten times the 
length of the other two together. Segment 7 is very small and 
inconspicuous, and segment 722 is composed of the labella. 
Throughout the whole length of the labium is the dorsal groove, 
in which lie the labrum and hypopharynx. This dorsal groove 
is deep in the basal part and becomes gradually more and more 
shallow distally. Near the extreme base it is practically closed 
above by the overlapping of the dorsal margins of the labium. 
(Plate XXXIV, Fig. 3.) 
The outer chitinous walls of the labium are comparatively 
thin but very hard, while the interior is completely filled by 
muscles and trachee. (Plate XXXIV, Fig. 3 me. and ir.) 
Segment a of the labium, as has been said, is very small, 
and appears as a small section of chitin in the joint between 
a and wm. Segment iz is composed of the labella, fitting 
together as one might place the palms of the hands together 
with the fingers pointing forward. Around the margins of the 
labella, under low power, smaller and larger hair-like processes 
may be seen projecting, while if a labellum be removed and its 
inner surface examined under the microscope its structure will 
be found to be elaborate and interesting. 
Figure 5 shows the inner surface of the right labellum, with 
its lower or ventral wall at vw, and the dorsal margin at dm. 
It will be seen that there are five strong chitinous teeth, ct., anda 
series of chitinous blades, cb., which are more delicate. In 
addition to these there are a number of longer or shorter sete 
on the distal and ventral margins. 
The Labrum (of Hansen) or upper lip, (Jb, Figs. 2, 3 and 4) 
(=labrum-epipharynx of Newstead) reaches nearly to the 
base of the labella. Its shape in section is readily seen from 
Figure 3, /b., where it will be noticed that its lateral margins are 
incurved below to form a definite tube with a rather broad slit. 
When feeding the tube is completed by the hypopharynx. (hp., 
in Figs. 2, 3 and 4). The labrum is thickened at the base, is 
somewhat strongly chitinised, and has a sharp, flattened, tri- 
