NO. 8 INSECT ABDOMEN SNODGRASS 69 



behind and below the bases of the cerci and the lower ends of the 

 lateral plates of the tenth tergum (fig. i8). The dorsal edges of the 

 paraprocts are connected by membrane with the lateral margins of the 

 epiproct (fig. 22 A, C), and their lower edges are united to each other 

 by a median ventral membrane, the posterior edge of which forms a 

 small median flap, or hypoproct (C, Hypt). The posterior margins 

 of the several lobes of the eleventh segment are inflected in the cir- 

 cumanal membrane, which is possibly to be regarded as a remnant of 

 the periproct, and which is directly continued into the walls of the 

 rectum. 



The cerci are implanted on membranous areas (fig. 18) surrounded 

 by the laterodorsal crescentic sclerites {q) above, the lateral plates 

 {p) of the tenth tergum anteriorly and ventrally, and the paraprocts 

 (Papt) behind. Each cercus has a distinct though narrow annular 

 basis (fig. 22 B, LB), which, as already observed, articulates by its 

 inner margin with the anterior arm of the small oval sclerite (r) 

 attached to the posterior end of the crescentic dorsal sclerite (q). 

 The appendage is provided with six muscles arising on the tenth 

 tergum (C). 



The musculature of the postgenital segments has little resemblance 

 to that of the genital and visceral segments and gives little evidence 

 bearing on the morphology of the terminal parts of the abdomen. 

 The tenth segment muscles are mostly inserted on the bases of the 

 cerci ; the muscles of the eleventh segment connect the epiproct and 

 paraprocts, and go to the circumanal membrane. The postgenital 

 complex is movable on the rest of the abdomen by the dorsal muscles 

 of the ninth segment inserted on the antecosta of the tenth tergum, 

 and in the male there is a strong ventral muscle on each side from 

 the anterior lateral angle of the ninth sternum to the inner face of 

 the paraproct. 



The muscles arising on the tenth tergum include the muscles of 

 the cerci, two pairs of rectal muscles, and a pair of muscles to the 

 paraproct. Du Porte (1920) describes and figures for Grylliis a dorsal 

 longitudinal muscle lying " near the median line of the suranal plate, 

 stretching from the anterior to the posterior borders of the sclerite " ; 

 but the writer could find no such muscle present, and no corresponding 

 muscle is mentioned by Ford (1923). The muscles of the tenth and 

 eleventh segments, illustrated at C of Figure 22, are the following: 



II. — A broad, flat, transverse muscle arising medially on tenth ter- 

 gum ; inserted on anterior arm of the small sclerite (B, r) articulating 

 with dorsal margin of base of cercus. 



