AQUATIC INSECTS 



3. Head-capsule complete, not retractile into thorax, — i. e. 



encephalous. 4 



Head-capsule incomplete, capable of retraction within 



body. 7 



4. Body depressed, subdivided into six primary divisions, 



each with a ventro-median sucking disk, with a tuft 

 of gills on either side. 



Net- veined midges, BlepharoceridcE, p. 297 

 Body not as above. 5 



5. Thoracic segments fused into a complex mass, without 



prolegs; in most genera with an anal respiratory funnel. 



Mosquitoes, CulicidcE, p. 293 



Thoracic segments not so fused ; if conspicuously dilated 



or extended, provided with a median prothoracic 



proleg. 6 



6. Body with conspicuous anal gills, or else long, slender 



and snakelike {Culicoides); no mouth-fans or caudal 

 sucking disk. Midges, ChironomidcE, p. 289 



Body not as above, the abdominal spiracles small but 

 distinct ; body club-shaped ; mouth with fans ; a sucking 

 disk on the club-shaped posterior end of body. 



Black-flies, SimuliidcE, p. 296 



7. Head massive, incomplete behind; mandibles moving 



horizontally or obliquely across the mouth-opening; 

 labial plate well developed. 



Cranefiies, (Tipuloidea), p. 283 



Head-capsule reduced, more or less retractile: mandibles 



moving vertically across the mouth-opening; labial 



plate not developed. 8 



8. Body depressed, spindle-shaped, the surface finely 



shagreened; head little retractile; spiracular fissure 

 transverse; pupates in last larval skin. 



Soldier-flies, StratiomyiidcB, p. 299 



Body cylindrical, the abdominal segments with a girdle 



of pseudopods on each segment; body-surface usually 



longitudinally striated; head retractile; spiracular 



. fissure vertical; pupa free, not in last larval skin. 



Horse-flies, TabanidcE, p. 298 



Cranefiies, Superfamily Tipuloidea. — Cranefiies are the 

 large mosquito-like insects which rest on the streamside 



283 



