a handbook of the mosquitoes of north america - Systematic Catalog ...

CHARACTERISTICS 21
the anterior margin of the head, and is attached between the
clypeal spines ; two lateral portions, each of which has at-
tached to it a dense mass of long yellow hair and which form
the well known Plzozl.t/z-brzzslzes. By means of muscles these
mouth-brushes can be moved rapidly backwards and forwards
producing a lashing motion.
_ Directly under the labrum lie the mandibles, large and elab-
drate in structure. The apices facing each other bear large
chitinous teeth. Directly below these is a large movable blade-
like structure, foIllowed by five other smaller ones which curve
inwards and forwards. These arise from a deep hollow, the
lower portion of which extends inwards in an elaborate struc-
ture bearing two projections provided with long hairs at their
tips. The base also bears hairs. The anterior margin bears
a large mass of hairs on its outer angle followed by three
large articulated spines. On the inner face, just below the
insertion of the retractor muscle, is a group of long hairs di-
rected inwards. The mandibles are moved by two powerful
muscles, a retractor and an extensor muscle. The maxillae
are large, flattened structures showing few of the details found
in mandibulate insects. The palpi are short and bear several
cone-like structures at their apices. Closing the mouth on the
ventral side is the labium. Anteriorly this consists of a heavily
chitinized triangular plate with a serrate margin-the labial
plate of authors. The labial plate is articulated to the anterior
edge of a large, median, ventral sclerite. The further details
of the structure of the labium and hypopharynx may be omit-
ted here. The shape, serrations, etc., of the labial plate are of
importance in systematic work.
The Thorax
The thorax consists of three fused segments. It is broad,
somewhat flattened and without any prominent angles. There
is a prominent row of long and short hairs along its anterior
margin, and prominent lateral and dorsal tufts of long hairs.
The arrangement of these hairs and hair tufts indicates the