CLASSIFICATION OF ANIMALS 179 



1 (2) With three pairs of legs, often with wings Insecta 



2 (1) Not with three pairs of legs, never with wings. . . 3 



3 (4) With four pairs of legs, no distinct head Arachnida 



4 (3) Not with four pairs of legs 5 



5 (6) Legs similar throughout body 7 



6 (5) Legs usually not similar throughout body, usu- 



ally aquatic Crustacea 



7 (8) A distinct head present Myriapoda 



S (7) No head, tropical Onychophora 



(u) The following key is for the adults of the more important 

 orders of aquatic insects. If you are trying to classify an immature 

 insect, use another key designed for that purpose. 



1 (2) Mouthparts are biting jaws which move side- 



ways 3 



2 (1) Mouthparts form a sucking tube 11 



3 (4) Without wings, very minute Aptera 



4 (3) With wings 5 



5 (6) First (outer) pair of wings hard, meet in a 



straight line down the middle of the back; 



beetles Coleoptera 



6 (5) Wings membranous 7 



7 (8) Abdomen with long filaments protruding from 



posterior end; may-flies Ephemerida 



8 (7) Abdomen without long filaments 9 



9 (10) Antennae short; dragon-flies and damsel-flies. . .Odonata 



10 (9) Antennae very long; caddis-flies Trichoptera 



11 (12) Four wings ; bugs Hemiptera 



12 (11) Two wings; flies, midges, etc Diptera 



