54 The Classification of Insects 



KEY TO THE ORDERS OF INSECTS. 

 (ARRANGED BY PROF. H. E. SUMMERS.) 



(For adult insects only. If in any paragraph all the italicized characters agree with 

 the specimen in hand, the remaining characters need not be read; these latter are for use 

 in doubtful cases, or where the organs characterized in italics are rudimentary or absent. 

 The technical terms used in this Key have all been denned in Chapter I.) 



A. Primitive wingless insects; mouth-parts well developed, but all except the apices of the 

 mandibles and maxilla -withdrawn into a cavity in the head; tarsi (feet) always one- 

 or two-clawed; body sometimes centiped-like, with well-developed abdominal legs, 



in this case tarsi two-clawed (The simplest insects.) APTERA. 



AA. Normally -winged insects, wings sometimes rudimentary or absent; mouth-parts 

 not withdrawn into a cavity in the head. 



B. Mouth-parts, when developed, with both mandibles and maxilla fitted for biting; 

 abdomen broadly joined to thorax; tarsi never bladder-shaped; when mouth- 

 parts are rudimentary, if the wings are two, there are no halteres (p. 303) ; if 

 the wings are four or absent, the body is not densely clothed with scales. 

 C. Posterior end of abdomen -with a pair of prominent unjointed forceps-like 

 appendages; fore wings, when present, short, veinless, horny or leathery. 



(Earwigs.) EUPLEXOPTERA. 



CC. Posterior end of abdomen usually without prominent unjointed forceps-like 

 appendages; when these are present the fore wings are always developed, 

 veined. 



D. Fore wings, when present, veined and membranous, parchment-like or 

 leathery; when absent, the labium (under-lip) either cleft in the 

 middle, or the mouth-parts prolonged into a distinct beak. 

 E. Fore wings, when present, thicker than hind wings, somewhat 

 leathery or parchment-like; hind wings folded several times 

 lengthwise, like a fan, in repose; when wings are absent, pro- 

 thorax large. 



(Locusts, crickets, cockroaches, etc.) ORTHOPTERA. 

 EE. Fore wings membranous, of same structure as hind wings; 

 hind wings usually not folded, but occasionally folded like a fan; 

 when wings are absent, prothorax small. 

 F. Antenna inconspicuous. 



G. Hind wings smaller than fore or absent; posterior end of 



abdomen with two or three many-jointed filaments. 



(May-flies.) EPHEMERIDA. 



GG. Hind wings not smaller than fore; postejior end of 

 abdomen without many-jointed filaments. 



(Dragon-flies and damsel-flies.) ODONATA. 

 FF. Antenna conspicuous. 



G. Tarsi less than five-jointed; labium cleft in the 

 middle. 



H. Wings always present, although sometimes very 

 small; hind wings broader than fore wings, 

 folded in repose; prothorax large, nearly flat 

 on dorsal surface. 



(Stone-flies.) PLECOPTERA. 



