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 defined in Chapter I.) 
A. Primitive wingless insects; month-parts well developed, but all except the apices o} the 
mandibles and maxillce withdrawn into a cavity in the head; tarsi (feet) always one- 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not withdrawn into a cavity in the head.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 maxillce 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, parchmer^t-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. Antennce 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; posterior end of 
abdomen without many-jointed filaments. 
(Dragon-flies and damsel-flies.) Odonata. 
FF. Antennce 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. 
