Postembryonic development and homology of external genitalia in Galloisiana nipponensis (Caudell et king) (Notoptera : Grylloblattidae)

Abstract

The postembryonic development of genital and postgenital segments of Galloisiana nipponensis (Notoptera : Grylloblattidae) have been described in detail. The coxite, stylus, epiproct and paraproct are already observed in the first nymphal instar, but the sexual characters are almost indistinguishable in the 1st to 4th nymphal instars, because the genital segments in these stages are not yet differentiated. In the 5th nymphal instar in the male, the paired primary phallic lobes start to appear at the hind margin of the 9th sternum. The rudiments of ventral valvulae in the female originate at the hind margin of the 8th sternum. In the 6th nymphal instar, the rudiments of inner valvulae begin to appear on the 9th sternum, in addition to the ventral valvula rudiments. The long dorsal valvulae are formed from the extension of nymphal coxite, while the nymphal styli are more reduced than those of younger instars. The ventral valvulae of the 8th abdominal segment are thought to be homologous with the inner valvulae of the 9th segment, judging from their site and mode of development. Further, the inner valvulae may also be homologous with the primary phallic lobes (phallomeres) of the male. The external genitalia in G. nipponensis originate from 2 structures: the dorsal valvulae (considered of appendicular origin), and the phallomeres; ventral and inner valvulae are regarded as mere integumentary outgrowths.