238 
tinues into the under surface of the head. 
Throughout its length it contains, on 
each side, muscles, which have their 
origin in the base of the head and serve 
to control the motions of the labium. 
(See figs. 8 and 9, mi.) At the sides of 
the tip of the labium are attached two 
lobiform appendages, the labellae, which 
are seen at /b in fig. 8 with the true tip 
of the labium proper between them. 
These terminal lobes are jointed to the 
labium, a little distance behind its tip, 
as can be seen in fig. 7, which is a cross- 
section of the labium a trifle anterior to 
the actual centre of motion of these 
joints. The section of that portion of 
the labium which extends forward to 
form its tip is seen in the middle of the 
figure, just below the section of the 
maxillae (ma). Outside the section of 
each lobe is seen the section of a portion 
of the exterior edge of the labium itself, 
which here forms a double socket, or 
pair of acetabula, into which the heads 
of the two labellae are set. Each of the 
lobes of the labium, —the labellae, — 
is provided with an extensor and flexor 
muscle (fig. 7, me, and mf), and is at- 
tached to the labium by a true joint. 
The labium has for function, for the 
most part, the protection of the fine 
setae which form the true piercing organ 
of Culex. In the females of Culex 
proper, the protective sheath is formed 
by the labiam alone. When the mos- 
quito has found a place which suits its 
taste for piercing, it plants its labellae 
firmly upon the spot, and a moment 
later the labium flexes backward in its 
middle, the setae, firmly grouped to- 
gether, remain straight and enter the 
PSTCOHE. 
skin, while the two labellae guide them, 
much as a carpenter guides his bit with 
his fingers, while boring a piece of plank. 
When the setae of Culex have entered 
the skin to nearly their full length the 
labium is bent double beneath the body 
of the insect, the labellae still holding 
the base of the setae at the point where 
they enter the skin. When the mos- 
quito wishes to withdraw the setae it 
probably first withdraws the two barbed 
maxillae beyond the other setae, that 
is, so that their barbs, or papillae, will 
be kept out of action by the mandibles 
and hypopharynx ; then it readily with- 
draws the setae, perhaps aiding their 
withdrawal by the muscles of the labium, 
for, during the process of extracting the 
setae from the skin, while they are slow- 
ly sinking back into the groove upon 
the upper side of the straightening la- 
bium, the mosquito keeps the labellae 
pressed firmly upon the skin. 
The mouth-parts of Culex, as above 
described, are suspended under a cly- 
peus, or epistom, which is figured from 
the side in fig. 1, ¢; from above in fig. 
2, c; in length-section in fig. 11, ¢; and 
in cross-section in fig. 9, ¢. This clypeus 
is the hood-shaped forward continuation 
of the lower part of a A-shaped piece 
of chitin which forms the framework of 
what may be termed the ‘‘ face” of 
Culex; right and left of the upper por- 
tion of this framework pass out the an- 
tennal nerves, the antennae being sup- 
ported by the framework itself. 
The pharynx (fig. 11, p), the tubular 
continuation of the epipharynx above 
and the hypopharynx below, as it passes 
backward, beneath the centre of the A- 
