NO. 8 



INSECT ABDOMEN SNODGRASS 



33 



•We may assume, therefore, that the first of the three median genital 

 invaginations occurred primitively on the posterior part of the seventh 

 venter, and that, by union with the mesodermal oviducts (fig. 8 A, 

 Odl), it became the primary median outlet tube of the ovaries, or 

 oviductiis communis {Ode'). The duct retains the primitive position 

 of its opening in adult insects only in Dermaptera. 



The second median genital invagination is formed on the posterior 

 part of the venter of the eighth abdominal segment (fig. 8 A, Spt), 

 and gives rise to a pouch for the reception of the spermatozoa. This 

 invagination is the spcnnatheca, or reccptaculum seminis. The sper- 

 matheca is usually a single organ, though it may be double or triple. 

 A diverticulum of its duct commonly forms a tubular spermathecal 

 gland. 



vns 



AcGl 



B 



Fig. ; 



VlllStn GC 



vuistn vns 



-Diagrams showing positions of ducts and associated structures of 

 the female genital apparatus. 



A, primitive condition, with median oviduct (Ode) opening on seventh seg- 

 ment, spermatheca (Spt) on eighth segment, and accessory glands (AcGl) on 

 ninth segment. 



B, usual condition, with oviduct (Ode) extended to end of eighth segment, 

 where it opens together with spermatheca (Spt) in a genital chamber (GC) 

 formed above eighth sternum. 



C, genital chamber (GC) enclosed in a vestibulum (Vst) formed above 

 seventh sternum (VI IS), accompanied by a reduction of eighth sternum 

 (VlllStti). 



D, unusual structure in Magicieada, in which genital chamber (GC) opens 

 from vestibulum by the primary copulatory aperture (a), but discharges the 

 eggs through a secondary posterior opening (/). 



The third median genital invagination is formed on the venter of 

 the ninth abdominal segment (fig. 8 A, AcGl). It is typically bifur- 

 cate, and gives rise to the accessory glands of the female genital ap- 

 paratus. These glands usually have a colleterial function, since they 



