262 ANIMAL BIOLOGY. [Part II. 



the middle of the metanotum. The posterior pair are repre- 

 sented by a reticulated pattern on the lateral edges of the meta- 

 notum. This suggests or illustrates the view which is otherwise 

 enforced by the study of development, that the wings of insects 

 are homologous with the free edges of meso- and metathoracic 

 terga. Such a wing arises as a sac-like fold of the chitinous 

 cuticle, which passes into the condition of a double lamina, 

 which, by the coalescence of its inner surfaces, becomes a con- 

 tinuous membranous expansion, strengthened by nervures which 

 take their origin in connection with the tracheal tubes. 



The abdomen of the female is broader than that of the male. 

 There are ten terga, of which the eighth and ninth are hidden 

 beneath the seventh. The tenth is large, of peculiar shape, 

 and notched posteriorly. The first sternum is small and rudi- 

 mentary ; the second large, with an irregular anterior border ; 

 the third and fourth are the broadest. The seventh is very 

 large, boat-shaped and cleft, a curious fold of integument being 

 visible when the two halves are opened out laterally. The 

 parts behind the seventh sternum are somewhat complicated. 

 This is largely due to the infolding of the cuticle to form a 

 genital pouch. The floor of this pouch is formed by the mem- 

 brane between the seventh and eighth sterna ; the back wall of 

 the pouch is formed by the large eighth sternum, which is per- 

 forated by the large genital aperture. In the dorsal wall lies 

 the ninth sternum, carrying the orifice of the spermatheca. 

 Further back is the anal opening. The parts are best studied 

 by removing all the ventral region posterior to, and including, 

 the seventh sternum, boiling in dilute caustic potash, and 

 examining under the simple microscope. When the relations of 

 the parts have been made out, the seventh sternum may be 

 carefully removed, and by cutting aloog the edges of the eighth 

 sternum and bending it back, the remaining parts may be 

 mounted, as shown in Fig. 80, D. In addition to the sterna 

 VIII. and ix., two pairs of appendages, which belong to these 

 somites, and which are termed gonapophyses, are seen. The 

 anterior gonapophyses (an. gon.) of the eighth somite are some- 

 what thumb-shaped, and are normally applied together in the 



