THE INSECTA 157 



The abdomen of the female cockroach is broader and flatter 

 than that of the male. The narrow terga of the eighth and 

 ninth segments are overlapped and concealed by the seventh 

 tergum in both P. americana and P. orientalis. The tenth 

 tergum is divided nearly into two by a notch extending forward 

 from the middle of its posterior margin ; under it lie the podical 

 plates and anus, as in the male. 



On the ventral surface only seven sterna are externally 

 visible. The seventh is very large and imperfectly divided 

 by a transverse groove into two parts, the posterior of which 

 is boat-shaped and divided into two lateral halves by a median 

 suture. Ordinarily these two halves are closely applied to 

 one another in the middle line; but they are connected by 

 a loose fold of soft and elastic cuticle which allows them 

 to be widely separated for the extrusion of the eggs or 

 the admission of the male organs in copulation. The 

 seventh sternum encloses a wide genital pouch formed by 

 the invagination of the eighth and ninth segments into the 

 segment preceding them. This invagination affects chiefly 

 the sternal moieties of the segments, so that the eighth 

 and ninth terga, though reduced and telescoped under the 

 seventh, retain their proper position on the dorsal surface, but 

 the sterna of the segments are carried far forwards to form the 

 anterior wall and roof of the anterior end of the genital pouch 

 (see fig. 40, A). The anterior wall of the pouch is formed by 

 the eighth sternum, a fairly broad semi-transparent chitinous 

 plate sloping from above downwards and forwards and pierced 

 by a median vertical slit, the opening of the female genital 

 duct. The ninth sternum is a small crescentic plate in the 

 roof of the pouch, the anterior edge of which is perforated by 

 a small pore leading into the spermatheca. The genital open- 

 ing is overhung by three pairs of more or less curved cylindrical 

 appendages called gonapophyses. The anterior pair of gona- 

 pophyses is the largest, and is attached to the upper edge of 

 the eighth sternum. The two posterior pairs are shown by 

 development to belong to the ninth sternum. 



From the above description it follows that in the male cockroach 

 the genital opening is between the tenth tergum and the ninth 

 sternum, while in the female it perforates the eighth sternum. 



The alimentary canal of the cockroach, like that of the 



