36 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 89 



genital chamber, being below and often behind the point at which the 

 spermatheca opens into the dorsal wall of the chamber. 



In some insects the spermatheca appears to arise from the dorsal 

 wall of the median oviduct, but it is probable that in all such cases 

 the part of the median egg passage receiving the spermathecal duct 

 is formed as an extension of the genital chamber. There can be no 

 doubt, for example, that the copulatory pouch of the cicada (fig. 32, 

 GC) or of the honey bee (fig. 44 B, b), into which the spermatheca 

 opens, is a part of the genital chamber, and it seems equally certain 

 that the so-called " uterus " of viviparous Diptera is likewise a special 

 compartment of the genital chamber. Since in most cases the genital 

 chamber receives the male organ during mating, it is functionally a 

 " bursa copulatrix ". When the genital chamber, or an anterior part 

 of it, however, takes the form of a tubular passage leading back from 

 the true oviduct, it should be called the vagina, as by Demandt (1912, 

 Korschelt, 1924) in Dytiscus, and by Imms (1930), Heberdey (1931), 

 and others, to disilnguish it from the true oviductus communis (Eier- 

 gang). Much confusion exists in descriptive works as to the distinc- 

 tion between median oviduct and genital chamber, or vagina. A safe 

 rule to follow is that the oviduct lies anterior to the mouth of the 

 spermatheca, and the genital chamber (vagina, or "uterus") pos- 

 terior to it. 



Morphologically the terminus of the oviductus communis in the 

 genital chamber, or vagina, should be distinguished from the posterior 

 opening of the latter to the exterior. The opening of the oviduct is 

 the true median gonopore, whether exposed externally, or concealed in 

 the genital chamber ; when the genital chamber is converted into a 

 copulatory pouch or a vaginal tube with a narrowed exit, its posterior 

 opening, whether on the eighth or the ninth segment, is the ostium 

 vaginae, or vulva. 



When the seventh sternum is extended beyond the eighth sternum 

 (fig. 8 C), the latter (VlllStn) is generally reduced in size, and may 

 become rudimentary, or it is retained only as a small plate on the floor 

 of the genital chamber containing the gonopore. This condition is char- 

 acteristic of Termitidae, Blattidae, Hemiptera, and Hymenoptera. 



The extension of the seventh abdominal sternum beyond the eighth 

 produces a second cavity (fig. 8 C, Vst) lying above the seventh 

 sternum, which becomes an antechamber to the primary genital 

 chamber (GC), or a continuation of the latter, and may be distin- 

 guished as the vestibulum. 



With insects that retain a generalized structure in the genital seg- 

 ments, the base of the ovipositor usually lies in the genital chamber. 



