285 



FAMILY CHARACTERS 



Larva. — Head complete ; mandibles opposed, toothed ; antennae 

 elongate; labial plate dentate anteriorly. Thoracic segments distinct, 

 rarely slightly swollen in Tanypinae ; prothoracic pseudopods present, 

 usually fused to or nearly to apex, and of moderate length, rarely very 

 short, always armed at apices with hairs or bristles. Abdomen consist- 

 ing of 8-9 segments ; apical segment in aquatic species with a dorsal 

 pair of papillae, upon which are several long hairs, and usually 2 or 4 

 small non-retractile blood-gills caudad of these and between the bases 

 of the posterior pseudopods, the apical claws of the latter normally re- 

 tractile, ventral blood-gills sometimes present; apical segment in ter- 

 restrial forms without dorsal papillae, with small pseudopods, the 

 blood-gills small and wholly or partly retractile; larvae peripneustic, 

 at least with minute lateral abdominal spiracles which may not func- 

 tion, or metapneustic, respiration being carried on by means of the 

 anal papillae and blood-gills ; body without strong hairs or bristles, 

 sometimes with numerous soft hairs. 



Pupa. — Antennae elongate, curved over upper margin of eyes; 

 head without spines, occasionally with a pair of conical tubercles at 

 base of antennae. Thoracic respiratory organs usually elongate, rare- 

 ly sessile, located near anterior margin of thorax; wings extending 

 slightly beyond base of abdomen ; legs elongate but recurved against 

 venter so that they project but little if any beyond apices of wings. 

 Abdomen circular or oval in cross-section, either without long hairs 

 or prominent bristles or the former confined to the lateral margins 

 and strap-like, and the bristles small and located on disc of segments 

 or at their apices; apical segment with 2 more or less flattened, fin- 

 shaped appendages. 



Imago. — A great majority of the species resemble mosquitoes in 

 their general build. The costa is, however, not continued round the 

 entire wing; there are no scale-like hairs on the wings; and the mouth- 

 parts are not constructed for piercing, being usually poorly developed. 



HABITS OF LARVAE 



By far the greater number of the species are aquatic in the larval 

 and pupal stages, only a few of the more specialized species in Chiro- 

 nominae being terrestrial. The food of the aquatic forms consists of 

 algae, decaying vegetable matter, diatoms, and small Crustacea. The 

 terrestrial forms known to me occur in manure and decaying vege- 

 table matter. 



