277 



to give an extended review of the species here, the principal divisions 

 being indicated only. Students who may desire a fuller knowledge of 

 the family characters should consult the papers listed herewith. 



I have retained Dixidae as a distinct family, contrary to the opin- 

 ion of some writers who consider that the group should be ranked as 

 a subfamily of Culicidae. 



FAMILY CHARACTERS 



Larva. — Head large, complete, exposed; mandibles moving hori- 

 zontally; antennae well developed ; mouth-brushes present (Culicinae) 

 or absent (Corethrinae, pt.). Thoracic segments fused, appearing 

 as a complex mass. Respiration carried on by means of posterior 

 spiracles which open on last segment, their tips frequently in the form 

 of elongated tubes, by means of which the larvae obtain a direct con- 

 nection with the air by piercing the surface film of the water in which 

 they live. In some of the Corethrinae there are present in the thorax 

 and in the apex of the abdomen a pair of air-sacs which are usually 

 black and conspicuous, contrasting with the glassy appearance of the 

 larval body. These species do not keep a connection with the air, and 

 are frequently found at great depths in lakes. Body with more or less 

 conspicuous hairs or hair tufts. 



Pupa. — As in the larvae, the thorax is conspicuously swollen; the 

 respiratory organs are placed well back on the sides of the disc of the 

 thorax — a characteristic that distinguishes the family from the Chiro- 

 nomidae. The abdomen has conspicuous hairs, some of those on the 

 dorsum being stellate, and its apex is usuallv armed with 2 or 4 large, 

 flat, paddle-like organs. 



Imago. — Readily distinguished by the tomentose or scaled wings, 

 slender build, long legs, complete marginal wing-vein; and by the 

 absence of ocelli, of discal cell of wing, and of the v-shaped dorsal 

 thoracic suture. 



HABITS OF LARVAE 



The larvae are aquatic, living under a variety of conditions, some 

 of them in very deep w^ater in lakes, some in shallow permanent pools, 

 others in ditches that offer a permanent breeding-place or in water in 

 depressions or receptacles that are of a temporary nature. The food 

 of the species differs considerably, some of them being almost entire- 

 ly vegetarian in habit, feeding on decaying detritus in the water or 

 upon algae, while others are predaceous, feeding upon insect larvae 

 and other small animals. 



