DIPT ERA. 261 



into the flesh. The blood is then sucked up the tube 

 formed by the labrum-epipharynx (PL XIII., Fig. 208, 

 lae) and the hypopharynx (Fig. 208, hyp; see PI. 

 XIII., Fig. 210, longitudinal section of the head), 

 and passes into the pharynx (Fig. 210, ph), oesopha- 

 gus {cs), and oesophageal bulb («^^), the valve (pv) 

 preventing its return. At the same time it is prob- 

 able that a poisonous liquid passes downward along 

 the upper side of the hypopharynx : if is the infra- 

 oesophageal ganglion ; sp, supra-oesophageal ganglion ; 

 cl, clypeus. 



The eggs of mosquitoes are usually laid in boat- 

 shaped masses on the surface of standing water, and 

 the larvae (PL XIII., Fig. 211) are familiarly known 

 as ''wigglers." They have a distinct head, and jaws 

 fringed with hairs, which help to catch the food. The 

 thorax is without legs, but both this region and the 

 abdomen are provided with clusters of hairs. The 

 larvae swim with the head downward, and breathe by 

 means of the respiratory tube (///) at the end of the 

 body, which connects with tracheae. They also often 

 suspend themselves just below the surface of the water 

 for the purpose of breathing. The pupae (PL XIII., 

 Fig. 212) respire by two tubes (///) on the thorax, 

 and motion is effected by leaf-like appendages (PL 

 XIII., Fig. 213) attached to the abdomen. They 

 take no food, and usually remain quietly near the sur- 

 face of the water, with the head upward ; though if 

 disturbed, they become active, their movements being 

 produced by the muscles of the abdomen, unaided 

 by those of the thorax. When they moult, the cast- 

 off skin serves as a raft, on which the insect rests till 

 its wings are ready for flight. 



