NO. 14 INSECT ABDOMEN SNODGRASS 83 



of their anterior parts (F), in others they are continuous end to end 

 in an arch over the ahmentary canal (B, C, D, E, G). The sperm 

 tubes of the united ducts are either distributed along the lateral or 

 anterior parts of the ducts (B, C, D, E), or they are clustered at the 

 point of union (G). The various types of male organs found in the 

 order are described and illustrated by Klapalek (1896) and Mertens 

 (1923), and a more detailed account of their structure is given by 

 Schoenemund (1912) for species of Perla, and by Wu (1923) for 

 Nenwura vallicularia. In the male of Perla marginata, in which the 

 united vasa deferentia form a large loop from one side to the other, 

 the gonadial tubes of the anterior part of the arch, as shown by 

 Schoenemund (fig. 28 E), during a late larval stage take on the form 

 of small ovarioles {ET) and contain egglike cells, while those of the 

 lateral parts form large oval testicular sacs {ST) in which the sper- 

 matozoa are developed. Each male ovariole, according to Schoene- 

 mund (1912) and Junker (1923), has the structure of a typical pano- 

 istic egg tube with a series of 12 to 18 oocytes enclosed individually 

 in cellular follicles. At an earlier larval stage, Junker observed, the 

 egg tubes are enclosed in a pair of ovarial sacs, or " male ovaries " 

 (D, MOv), situated on the median part of the arch of the duct, but 

 he says a few oocytes are to be found also in the saclike sperm tubes 

 {ST). The "male eggs" of Perla marginata, however, were found 

 by Junker to possess the diploid chromosomes of the spermatic cells ; 

 they never complete normal maturation, and the tubules containing 

 them degenerate at the transformation to the adult. 



The vasa deferentia are generally enlarged toward their posterior 

 ends to form storage vesicles for the spermatozoa (fig. 28 A, G, H, J, 

 Vsm). In some forms a tubular diverticulum (J, k) is given off from 

 each duct. Klapalek describes a condition in species of several genera 

 in which the two ducts are connected by a transverse vessel (B, /) 

 looped forward between them, which he regards as a vesicula semi- 

 nalis. In Leiictra, according to Klapalek and Mertens, a sperm vesicle 

 in the form of a median pouch arises at the junction of the vasa 

 deferentia with the ejaculatory duct (A, Vsm). 



The median genital exit system of male Plecoptera varies con- 

 siderably among different genera in the relative development of its 

 parts, and the identities of the latter are difficult to follow in pub- 

 lished descriptions of the genital organs. In a freshly dissected 

 specimen of Acronciiria (fig. 28 I) the two tubular vesiculae seminales 

 {Vsm) appear to discharge directly into a large sac {Enph) opening 

 through the ectophallus {Phi) ; but if the parts are pulled out length- 

 wise (J) it is seen that there are short terminal sections of the vasa 



