1922] Walker: Structure of Orthopteroid Insects 53 



Summary of the Characteristics of the Orders. 



BASED ON the TERMINAL ABDOMINAL STRUCTURES 

 OF THE MALES. 



Ephemerida. Terminal segments (9-10) well developed; 

 ninth sternum consisting of sternite and coxites, which may 

 be separate or united, and bear long jointed styli; supra-anal 

 plate feebly developed, but a telofilum present, generally long 

 and multi-articulate like the cerci; paraprocts but little 

 developed and largely or wholly membranous; genitalia con- 

 sisting of double symmetrical penes, with or without parameres; 

 virga absent in the forms studied; post-sternum present or 

 absent. 



Dermaptera. Terminal segments all distinct, none reduced; 

 the tenth tergum greatly enlarged; ninth sternum forming a 

 large, undivided hypandrium without styli; cerci very large, 

 forcipate, unsegmented (except in immature stages of some 

 genera) ; supra-anal plate divided into two or three segments, 

 the second and third perhaps representing a vestigial telofilum; 

 paraprocts in the form of thin, fiat, free plates, occupying the 

 sternal region of segment 10, there being no true tenth sternum 

 in the types studied; penis elongate, bifid or double, with 

 paired apertures, or single with one aperture; a virga or virg^e 

 present; also a pair of parameres, usually lateral or dorso- 

 lateral arising from the walls of the penis. 



Embiidina. Terminal segments distinct, the ninth tergum 

 shortened, the tenth large, somewhat asymmetrical and divided 

 more or less completely into hemitergites bearing dissimilar 

 copulatory processes ; ninth sternum forming an asymmetrically 

 triangular hypandrium, terminating in a copulatory process, 

 without separate coxites or styli; cerci two-jointed, slightly 

 asymmetrical, with rather large basipodites, of which the left 

 may bear a copulatory process ; the various copulatory processes 

 converging toward the left side; supra-anal plate and para- 

 procts undeveloped (or vestigial) ; penis absent. 



In the primitive genus Clothoda the parts are symmetrical, 

 the tenth tergum undivided, the basipodites very large and 

 projecting inward and the copulatory processes all absent. 



Plecoptera. Terminal segments well developed, but not 

 elongated, the ninth and tenth often more or less annular; 



