NO. 8 INSECT ABDOMEN SNODGRASS 67 



duced automatically by an extreme retraction of the dorsal valvulae, 

 which brings a pair of knobs (C, n) on their under surfaces against 

 abruptly rising areas on the upper surfaces of the ventral valvulae, 

 with the result that the distal parts of the dorsal valvulae, beyond the 

 membranous hinges (in) at their bases, are suddenly thrown upward 

 (D). The opening apparatus probably enables the cricket to hold the 

 egg in the tip of the ovipositor so that it may be thrust securely into 

 the bottom of the hole where it is deposited. This use of the ovipositor 

 the writer has clearly observed in the case of Nemohius ovipositing 

 against the wall of a glass jar. 



The postgenital segments. — ^The tenth and eleventh segments of the 

 abdomen together form a conical end piece of the body, which sup- 

 ports the cerci laterally and encloses the anus between its distal 

 lobes (fig. 22 A). 



The tenth tergum and the epiproct (fig. 22 A, XT, Eppt) are united 

 in a composite supra-anal plate, but the boundary separating the two 

 component parts of the plate is quite evident. The narrowed anterior 

 lateral angles of the dorsal part of the tenth tergum are continued 

 into abruptly widened lateral plates (fig. 18, p), which are produced 

 ventrally on the sides of the tenth segment, before the bases of the 

 cerci, to the lower angles of the paraprocts (Papt). The venter of 

 the tenth segment is mostly membranous, but it contains a narrow, 

 transversely elongate sternal sclerotization (fig. 22 C, XStn). In- 

 ternally the anterior margin of the tenth tergum is strengthened by a 

 strong antecosta (Ac). The dorsal part of the tenth tergum is sepa- 

 rated from the base of the cercus on each side by a wide mem- 

 branous area containing a small crescentic sclerite (A, q). 



The tergum of the eleventh segment, or epiproct, consists of the 

 distal lobe of the supra-anal plate (fig. 22 A, Eppt). Its marginal 

 parts (s) are separated from the median shield-shaped region by a 

 narrow, weakly sclerotized or membranous area on each side. The 

 marginal band (s) appears to end anteriorly at the transverse folds 

 extending outward from the posterior edge of the tenth tergum to 

 the bases of the cerci. Considering, however, that the cerci belong 

 to the eleventh segment, and observing that in Scudderia (fig. 12) 

 the basal angles of the epiproct (Eppt) are produced into slender 

 arms extending forward and downward anterior to the bases of the 

 cerci, there is reason to believe that the marginal band of the epiproct 

 in Gryllus is morphologically continued anteriorly in the narrow cres- 

 centic sclerites (fig. 22 A, q) lying mesad of the bases of the cerci, 

 which appear to belong to the dorsum of the tenth segment. When 

 the area about the base of the cercus is stretched and flattened out 



