NO. 14 INSECT ABDOMEN SNODGRASS 81 



other insects are either reduced or suppressed in both sexes of the 

 stoneflies. In the female the gonotreme, or vulva, lies above the pos- 

 terior margin of the eighth abdominal segment (fig. 29 C, Gtr), where 

 it opens from a small genital chamber containing the oviducal and 

 spermathecal apertures ; but an ovipositor is entirely absent. The two 

 small processes borne by the eighth sternum in females of Pteronarcys 

 are clearly not true gonapophyscs, since the latter always arise pos- 

 terior to the sternal plate. In some forms the lateral oviducts appear 

 to discharge separately into the genital chamber (vagina), in others 

 they first unite with a very short oviductus communis (see Klapalek, 

 1896; Mertens, 1923; Wu, 1923). The genital segments of the male 

 have no appendicular organs that can be referred to segmental limbs, 

 comparable with the styli of apterygote insects, Ephemerida, and 

 Orthoptera, or with the movable claspers (harpagones) of other 

 Pterygota. The functional intromittent organ is in most cases a phal- 

 lic structure, though a median process of the epiproct has been de- 

 scribed as a " sperm conveyor ", and in the genus Leiictra it is possible 

 that a pair of ventral processes of the tenth segment conduct the sperm 

 to the female from the male genital opening situated at their bases. 

 In the families Pteronarcidae and Perlidae the " penis " is principally 

 a large, eversible endophallic sac, accompanied or not by an ectophal- 

 lus ; in the other families, Nemouridae and Capniidae, there may be 

 present a short tubular ectophallus, which contains the opening of the 

 genital exit passage, but the latter has not been shown to be eversible. 

 The occurrence of " paired penes " has been claimed, but not demon- 

 strated. Whatever accessory genital structures are present in the 

 Plecoptera are secondary processes, usually of the tenth and eleventh 

 abdominal segments, but also of the eighth and ninth. Information 

 on the exact function of the phallic organs and accessory genital 

 processes in the order is far from complete. 



The internal reproductive organs of the Plecoptera are highly 

 variable in the several families, particularly with respect to the group- 

 ing of the testicular tubules, and in the size and character of the 

 median exit duct. The testes have no peritoneal investiture, the sperm 

 tubes being free from one another, as are the tgg tubes of the ovaries, 

 and, so far as noted, the gonads have no suspensory ligaments in 

 either sex. Only in the genus Leuctra (Nemouridae) have the 

 vasa deferentia been described as being independent of each other 

 (Klapalek, 1896; Mertens, 1923) ; in such cases the testes consist of 

 groups of slender tubules arising from the anterior ends of the ducts 

 (fig. 28 A, Tes). In other forms the vasa deferentia of opposite sides 

 are united ; in some cases they have coalesced for a considerable length 

 6 



