1922] Walker: Structure of Orthopteroid Insects 3 



chitinized or wholly membranous. Where two apertures are 

 present there are likewise two penes (Ephemerida) or a more 

 or less deeply bipartite penis (Dermaptera), but it is probable 

 that in these orders the penis or penes are not strictly homol- 

 ogous with those of other orders; in fact it appears as though 

 the penis may have developed independently in several orders. 

 A slightly bipartite penis has been described as occurring also 

 in certain Plecoptera (Crampton, '18). The bifid termination 

 of the penis in some Acrididas simulates this condition slightly, 

 but is in no way comparable to it. Among the Apterygota w^e 

 find double penes in Eosentomon of the Protura (Prell, '13) 

 and a slightly bifid penis in certain genera of Lepismoidea, such 

 as Nicoletia (Escherich, '04), but the former is perhaps not 

 strictly homologous with the other case cited, as it is found 

 upon the eleventh instead of the ninth segment. The occurrence 

 of double penes is probably a very primitive condition, as 

 paired genital apertures are frequent in the more primitive 

 Arthropods, such as the Crustacea and Diplopoda. 



The penis is frequently eversible and in the everted con- 

 dition the chitinized terminal part of the ejaculatory duct 

 may project in the form of a spine, the virga. This structure 

 is most typically seen in the Dermaptera, and in such forms as 

 have a bifid penis the virga is likewise duplicated. It also 

 occurs in certain Blattids, and according to Crampton, in some 

 Plecoptera. The membranous eversible wall of the penis is the 

 glans or praeputial sac. 



There is also, primitively, a pair of chitinous processes, the 

 parameres, arising near the base of the penis or from its walls, 

 and having typically a lateral or dorsolateral position. They 

 are well illustrated by the Dermaptera and certain Ephemerida, 

 and it is probable that the titillators of most Orthoptera 

 (although not all the structures so-called) are their homologues. 

 It is uncertain, though in the writer's opinion probable, that the 

 parameres of the Thysanura are morphologically identical 

 with those of the pterygote insects. Crampton ('20) has 

 apparently confused the penes of the Ephemerida with the 

 parameres of other insects under the term "penis valves." 

 Chopard ('18) expresses the view that in the Orthoptera 

 (including the Blattoidea, Mantoidea and Phasmoidea) there 

 are two pairs of processes, which he terms the "valves dorsales" 

 and the "valves ventrales, " between which the genital aperture 



