THE LARVA. 
All mosquito larve are aquatic. They possess a complete, well-chitinized head 
with the typical mouth-parts of mandibulate insects. The thorax is broad and 
its three segments are fused. The abdomen is long and slender with nine well- 
defined segments. There are no ambulatory appendages. The anal opening is 
at the apex of the ninth segment and is surrounded by four more or less de- 
veloped tracheal gills. The tracheal system is metapneustic with the openings 
dorsally on the eighth segment, usually through a chitinous tube of greater or 
less length. The larve are active and move backward through the water by 
jerking the body from side to side. They also can move slowly forward by the 
action of the mouth-brushes. By means of a mechanism at the end of the respir- 
atory tube the larva can suspend itself from the surface film in order to take 
in air. Raschke has pointed out that the breathing tube has the further function 
of an hydrostatic apparatus. It will be most convenient to discuss in detail the 
structures of the larva of Culex and afterward point out the various modifica- 
tions that occur in other mosquito larve. 
THE HEAD AND MOUTH-PARTS. 
The head of the Culex larva is broad, rounded, and somewhat flattened. It 
is inserted upon the thorax by a narrow neck, the opening into the head being 
surrounded by a heavy chitinous collar, the foramen. The antenne are promi- 
nent and inserted anteriorly upon the outer angles of the head. Between the 
antenne the head is arcuate and a narrow clypeus forms its anterior margin. 
In front and beneath is the labrum with its appendages. The median free lobe 
of the labrum is attached between two long, stout spines which project forward 
and downward from the anterior margin of the clypeus. The other mouth 
organs are upon the ventral side of the head and the anterior part of the head 
may be considered a broad rostrum which projects over them. The eyes are 
placed laterally and consist of two pairs, the large compound eyes, and behind 
them the accessory eyes. 
The antenne consist of a single chitinous piece and are cylindrical and 
slightly curved. About two-thirds from the base the shaft is suddenly narrowed 
and at this point is inserted a fan-shaped tuft of long feathered hairs. The 
slender apical third is obliquely truncate at the tip. Upon the tip is inserted a 
conical sensory organ surrounded by three long sete and a shorter spine-like 
seta. Raschke interprets the sensory cone as an olfactory organ. It has a 
chitinous cylindrical basal portion with a minute spinous process upon its side 
and a very delicate conical sensory portion at the apex. The antennal shaft is 
beset with numerous small spines. The antenne have but little motility. They 
are controlled by a single rather weak muscle, inserted at the base and running 
backward to the hind margin of the head. The antennew are connected with the 
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