56 



SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 89 



male (A). The shortened eighth tergum (B, VIII) ends below in a 

 point separated by the dorso-pleural fold from the small eighth 

 sternum (VlllStn), which projects beneath the base of the ovipositor 

 as a small subgenital plate. The ninth tergum (IX) is narrowed above, 

 but is widened on the sides, and extends downward to the base of the 

 ovipositor. The venter of the ninth segment is not visible externally ; 

 it is the narrow, membranous ventral wall of the segment between 

 the basal halves of the ovipositor, containing anteriorly and posteriorly 



]5t dim 



J. 



PlStn 



V i_Stn_ ^< ^^ ^ C 



VNC . ve vi 



A 



C 



PlStn. 



Fig. 16. — Abdominal structures of Gryllus and Blatta. 



A, diagrammatic cross-section through abdomen of Gryllus assimilis, show- 

 ing relation of integumental areas and muscles illustrated in Figure 15. 



B, lateral parts of abdominal segment of Blatta orientalis with dorsal and 

 ventral plates separated to expose the dorso-pleural fold (a-a). 



C, diagrammatic cross section of abdomen of Blatta, showing infolded dorso- 

 pleural membrane (a), and position of lateral muscles (li). 



the sclerotic intervalvular bridges (figs. 17 H, 18, aiv, piv). In the 

 male the ninth sternum is fully exposed, and forms a large subgenital 

 plate (fig. 14 A, IXStn). The inner surfaces of the eighth and ninth 

 terga of the female (fig. 18) are enlarged by thin apodemal extensions 

 from their anterior margins, giving attachment to muscles of the 

 ovipositor. The ninth tergum has a strongly developed antecosa (Ac), 

 which terminates in a ventral process bearing a socket (a) for articu- 

 lation with the basal part of the ovipositor. 



The musculature of the genital segments is mostly adapted to the 

 mechanism of the ovipositor. The dorsal muscles, however, conform 

 with those of the visceral segments, and in the eighth segment there 

 are one or two pairs of weak lateral muscles inserted below near the 

 margins of the eighth sternum. The other lateral muscles in both 

 genital segments are highly developed as muscles of the ovipositor 

 (fig. 17 E). Ventral muscles are absent in the eighth segment, and 

 those of the ninth segment are of doubtful homology with the ventral 

 muscles of the visceral segments. 



