CLASSIFICATION 19 
15. Diptera.—Metamorphosis indirect. Mouth parts typ- 
ically suctorial, but modified for piercing, lapping, rasping, etc. 
Prothorax small. One pair of wings (mesothoracic), mem- 
branous, transparent, with few veins; wings rudimentary or 
absent, however, in most of the parasitic species; hind wings 
represented by a pair of knobbed threads, or balancers. Lar- 
vee eruciform, with the head frequently reduced to a mere 
vestige with or without a pair of mandibles, and usually with- 
FTG 27, 
Papilio troilus. A, larva; B, larva suspended for pupation; C, chrysalis. 
Natural size. 
out true legs, though pseudopods may be present. Example, 
Tipula (Fig. 29). About forty thousand described species. 
16. Siphonaptera (Aphaniptera).—Metamorphosis indi- 
rect. Head small. Eyes simple or absent. Mouth parts 
suctorial. Body laterally compressed. Thoracic segments 
subequal. Wings absent or at most quite rudimentary. Lar- 
ve with a head, mandibulate, apodous. Parasitic insects. 
Example, Ctenocephalus (Fig. 30). One hundred and fifty 
species. / 
17. Hymenoptera.—Metamerphosis indirect. Mouth parts 
at the same time mandibulate and suctorial. Prothorax usu- 
ally small. Wings four, similar, membranous, transparent, 
