NO. 8 INSECT ABDOMEN- — SNODGRASS 23 



egg passage thus conies to be a single median tube opening behind 

 the ninth sternum, receiving the lateral oviducts into its bifurcate 

 anterior section (c), and having a dorsal diverticulum (d) shortly 

 behind the branches, into which open the sperm receptacle (Spt) and 

 associated glands later formed. 



If the ontogenetic development of the female exit apparatus in 

 Coleoptera as given by Singh Pruthi and by Metcalfe represents 

 the phylogenetic course of evolution in this order, it v^ould appear that 

 the sperm receptacle of Coleoptera is not homologous with the sperma- 

 theca of other insects, which always (except possibly in Diptera) 

 takes its origin at the posterior margin of the eighth segment, and is 

 subsequently associated with the genital chamber invagination found 

 here. There is little in the adult structure of the female organs in 

 Coleoptera, however, to suggest that the exit apparatus in this order 

 is in any way fundamentally dififerent from that of other insects. The 

 large vaginal tube or sac (fig. 4 F, Vag) opening on the ninth seg- 

 ment usually has a dorsal pouchlike diverticulum (d), generally called 

 the " bursa copulatrix ", which it probably is in function. The sperm 

 receptacle opens either into the anterior part of the vagina (fig. 4F), 

 or into the diverticulum of the latter (fig. 5 B). Accessory glands are 

 usually absent. Since the genital tract in the mature condition has only 

 the single opening on the ninth segment, this aperture becomes in a 

 functional sense the vulva ( Vid) , though anatomically it corresponds 

 with the oviporus of Lepidoptera (fig. 4 E, Opr). 



In Diptera it is usually said the female genital opening lies on the 

 venter of the eighth segment behind the eighth sternum, and it 

 apparently does have this position in most families. According to 

 Metcalfe (1933), however, the opening occurs on the ninth segment 

 in the cecidomyid Dasyneiira leguminicola. The development of the 

 female efferent system in this insect, moreover, is shown by Metcalfe 

 to be closely parallel with that found in Coleoptera. The definitive 

 tgg passage, she says, is the product of a union between an ectodermal 

 invagination arising posterior to the eighth abdominal sternum, and 

 another formed posterior to the ninth sternum. The first branches 

 anteriorly, and its arms unite with the mesodermal oviducts ; the 

 anterior end of the second gives rise to the spermathecae and the 

 accessory glands. By a closure of the anterior opening, the secon- 

 darily continuous passage has its exit through the posterior opening 

 on the ninth segment. Thus, in Dasyneura, as in Coleoptera, it would 

 appear that the sperm receptacles are derived from the invagination 

 of the ninth segment, and not from that of the eighth, as in other 

 insects. 



