THOMPSON: ANATOMY OF MOSQUITO. 
149 
differently shaped head makes the angle with the door measure 
nearly thirty-dve degrees. The struts are provided with the seem¬ 
ingly useless spur near the foot, hut above expand suddenly to form 
the “head” and then the tube narrows again as it meets the cheeks. 
The mouthparts (pi. 16, dg. 46-47) of the mosquito need no 
elaborate description here. The usually accepted nomenclature will 
be employed for the various stylets. The labrum is horseshoe¬ 
shaped in section and forms the whole or the major part of the tube 
(pc) through which the insect sucks blood or other liquid. There is 
no good reason to retain the name labrum-epipharynx for this dor¬ 
sal stylet, with the consequent implication that the organ is com¬ 
pound. Becher long ago (’82) pointed out that the separation into 
two parts under manipulation was an artifact. Morphologically for 
the imago of Culex (pi. 16, dg. 46-47) and for the imagoes of other 
dies (Krapelin, ’82, ’83) the labrum is a unitary structure. During 
the metamorphosis of Culex also, the labrum is formed as a simple 
tube. The canal (pc) on its ventral face is moulded by the infold¬ 
ing of the ventral wall. The labrum receives a single muscle which 
probably serves for a retractor and depressor. This muscle is in¬ 
serted on the boss of chitin at the base of the labrum and its dbers 
arise from the dorsal and posterior walls of the clypeus. It may be 
called the labral muscle (pi. 12, dg. 2). This muscle has been de¬ 
scribed as “labral muscle ” (Annett and Dutton, :01), “elevator of 
labrum-epipharynx ” (Nuttall and Shipley,: 01-: 03), “retractor of la¬ 
brum” (Giles, : 02), and “retractor partes productae” (Meinert, ’81). 
It corresponds in part to the “pharyngeal muscle” of Dimmock 
(’ey _ _ 
The mandibles are wanting in the male mosquito and are slender, 
delicate lancets in the female. Dimmock (’81) has dgured these 
organs in the cross section of the mouthparts as lying beneath the 
hypopharynx. Giles (: 02) gives a similar arrangement in one fig¬ 
ure while in another he shows the mandibles above the hypopharynx 
at the sides of the labrum. This last is the proper position for the 
stylets when at rest. The mandibles are morphologically dorsal to 
the hypopharynx. The other position is due to misplacement dur¬ 
ing the processes of sectioning. Each mandible is retracted by a 
mandibular muscle (mnd m) which arises on the “ head ” of the 
tentorium and is inserted on the base of the stvlet. As these mus- 
cles approach their insertions short fibers connect them with the 
