The Classification of Insects 55 



HH. Hind wings, when present, not broader than fore 

 wings, not folded in repose; prothorax small, 

 collar-like. 



I. Tarsi four-jointed; wings, when present, 

 equal in size (Termites.) ISOPTERA. 



II. Tarsi one- to three-jointed. 



J. Tarsi one- or two-jointed; always 

 wingless. 



(Biting bird-lice.) MALLOPHAGA. 



JJ. Tarsi usually three-jointed; occasionally 



two-jointed, in which case wings always 



present, fore wings larger than hind 



wings. (Book-lice, etc.) CORRODENTIA. 



GG. Tarsi five-jointed, but with one joint sometimes 



difficult to distinguish; labium usually entire in 



middle, sometimes slightly emarginate. 



H. Wings, when present, naked or slightly hairy; 



hind wings with or without folded anal space; 



in former case prothorax large and nearly 



flat on dorsal surface; in wingless forms 



mouth prolonged into a distinct beak. 



I. Mouth-parts not prolonged into a distinct 

 beak, at most slightly conical. 



(Dobsons, ant-lions, etc.) NEUROPTERA. 



II. Mouth-parts prolonged into a distinct beak. 



(Scorpion-flies, etc.) MECOPTERA. 

 HH. Wings, when present, thickly covered with hairs; 

 hind wings usually with folded anal space; pro- 

 thorax small, collar-like; mouth not prolonged 

 into a beak. (Caddis-flies.) TRICHOPTERA. 



DD. Fore wings, when present, veinless; horny or leathery; when absent, 

 labium entire, and mouth-parts not prolonged into a distinct beak. 



(Beetles.) COLEOPTERA. 



BB. Mouth-parts, when developed, more or less fitted for sucking; sometimes also 

 fitted in part (the mandibles) for biting: in this case either (i) base of abdomen 

 usually strongly constricted, joined to thorax by a narrow peduncle, or (2) the 

 tarsi bladder-shaped, without claws; when mouth is rudimentary either the 

 wings are two and halteres are present, or the wings are four or none and 

 the body (and wings if present) are densely clothed with scales. 

 C. Prothorax free; body (and wings if present) never densely clothed with 

 scales; maxillary palpi usually absent; when present, tarsi bladder- 

 shaped, without claws. 



D. Tarsi bladder-shaped, without claws; wings four (sometimes absent), 

 narrow, fringed with long hairs; maxillae triangular, with palpi. 



(Thrips.) THYSANOPTERA. 



DD, Tarsi not bladder-shaped, usually clawed; wings not fringed with 



long hairs; maxilla (when mouth is developed) bristle-like, without 



palpi. (Bugs.) HEMIPTERA. 



CC. Prothorax not free; maxillary palpi present, sometimes rudimentary 



and difficult to see, in which case body (and wings if present) densely 



clothed with scales; tarsi never bladder-shaped, usually clawed. 



