NO. O INSECT ABDOMEN — SNODGRASS 21 



true oviduct, there are produced by invagination of the ectoderm two 

 median l)ilol)ed " vesicles ", one on the venter of the eighth abdominal 

 segment, the other on the venter of the ninth segment. The lips of the 

 anterior depression grow out in the form of two longitudinal folds, 

 which imite to form a tube. This is the middle section of the future 

 median passage. Its anterior end is then extended as a cellular growth 

 into the seventh segment, where it unites with the lateral mesodermal 

 ducts. This part becomes the anterior section (the true oviductus 

 communis) of the definitive egg passage. The anterior vesicle gives 

 rise also to the bursa copulatrix and to the spermatheca. The posterior 

 section of the egg passage appears first as a groove on the venter of the 

 ninth segment extending from the anterior vesicle to the vesicle of 

 the ninth segment, which latter forms the accessory colleterial glands. 

 There is thus eventually formed a continuous passage from the lateral 

 oviducts to the ninth segment, communicating with the exterior on 

 the eighth segment through the bursa copulatrix, and having a pos- 

 terior opening at the end of the ninth segment in common with that 

 of the accessory glands. The spermatheca opens into the dorsal wall 

 of the tube opposite the bursa copulatrix. 



In Coleoptera the female genital opening is situated on the venter 

 of the ninth abdominal segment of the adult. According to Heberdey 

 (1931), the rudiments of the unpaired duct and associated organs 

 of Hydroporus ferrugineus appear first in a young larval stage as 

 median invaginations on the posterior parts of the seventh and eighth 

 abdominal segments. The bifurcate anterior ingrowth unites with 

 the lateral oviducts ending in the seventh segment, and its median 

 posterior part constitutes the first section (Eiergang) of the definitive 

 outlet passage. The second section (vagina) is formed first as a 

 groove beneath the invagination of the eighth segment, which becomes 

 continuous with the opening of the anterior invagination, and which, 

 by closure of its lips, produces a tube extending posteriorly from 

 the lateral ducts, with the posterior invagination arising as a pouch 

 from its dorsal wall. When the ninth sternal plate is formed it lies 

 anterior to the rear opening of the tube, which latter thus comes 

 to be on the posterior part of the ninth segmental venter. By a peculiar 

 development in Hydroporus, as described by Heberdey, the median 

 tube is divided lengthwise into an upper part {bursa copulatrix and 

 receptaculum seniinis) and a ventral part {vagina), the two opening 

 separately on the ninth segment. 



The development of the median female duct in Tcnchrio uwlitor, 

 as described by Singh Pruthi (1924), is somewhat difl^erent from that 

 in Hydroporus, described by Heberdey. In a young pupa of Tenebrio, 



