86 MOSQUITOES OF NORTH AMERICA 
ing simultaneously. When these muscles contract the seta-bearing area of the 
flabella is depressed and the setze come together in a brush whose tip points 
caudad. On their relaxation the flabelle protrude beyond the front of the head 
and the sete stand out in great yellow fans. The median prominence or pala- 
tum passively follows the movements of the flabelle, which are strictly syn- 
chronous, as far as J have observed.” 
The palatum is clothed on its dorsal surface with short but coarse spine-like 
hairs; ventrally is inserted a dense tuft of long pendant hairs which swing in 
unison with the lateral brushes. In the region of the epipharynx are two 
fringes of dense hairs arranged in closely approximated longitudinal series. Ac- 
cording to Raschke the epipharynx when in repose reaches down to the hypo- 
pharynx and closes the mouth. In swallowing, the epipharynx is raised and 
drawn back by two muscles inserted at its base. 
The mandibles are large and elaborate in structure. In a ventral view they 
lie behind the maxilla and are in large part hidden by them. They are very 
broad and situated well apart. The apices facing each other bear a group of 
projecting irregular teeth and near these on the outer side a large movable spine 
is inserted. Below the teeth there is a broad truncate chitinous projection. On 
the dorsal margin is a series of seta-bearing tubercles and at the outer angle 
several long spines. On the inner side there is a fringe of long hairs, inserted on 
a crescentic chitinous ridge near the apical margin, which helps to sweep the 
food into the mouth. The mandibles are moved by two pairs of powerful 
muscles. A muscle attached to the lower inner angle draws the mandible down- 
ward and inward, another muscle at the outer lower angle draws it outward. At 
their opposite ends the muscles are broadly attached in the posterior part of the 
head to the epicranium walls. 
The maxille are large but very simple, showing none of the components trace- 
able in most mandibulate insects. They are flattened, roughly conical with a 
small basal appendage, the maxillary palpus, on the outer side. The maxille 
are situated upon the apical ridge of the under side of the hypocranium and 
cover the mouth from beneath. Like the mandibles they are well separated, 
leaving an open space between them, which is however closed by projecting hairs. 
There is a longitudinal suture and the surface is more or less hairy, particularly 
towards the apex where the hairs are dense and long. The small palpus bears 
at its apex several spine-like sensory appendages. Raschke does not think that 
this palpus can be homologized with the maxillary palpus of the typical mandib- 
ulate insects and he points out that different components of the maxilla of 
such insects can not be traced in the maxilla of the mosquito larva. The 
maxille are broadly attached to the hypocranium by a membrane and but 
slightly movable. Two weak muscles effect the movement of each maxilla, both 
inserted at the middle of the base and passing back are attached posteriorly to 
the epicranium walls. 
A broad median region of the hypocranium, bounded by strong longitudinal 
sutures, constitutes the mentum. 
At the attachment of the maxille the hypocranium terminates in a sharp 
transverse ridge, somewhat lobed outwardly from the maxille. Behind this 
