NO. 8 INSECT ABDOMEN— SNODGRASS 75 



lobes are united by a wide inflected membrane, and from their inner 

 surfaces there are produced laterally two high membranous folds. The 

 space between these folds can be greatly expanded by the extension of 

 the ventral membrane, thus forming a pocket in which the ootheca is 

 lodged. All this extension and modification of the seventh sternum is 

 clearly an adaptation for the formation and retention of the egg case. 

 In the structure of the female genital apparatus, therefore, the roach 

 is highly specialized. The oothecal pocket is a part of the vestibulum 

 (fig. 23, Vst), at the anterior end of which is the small true genital 

 chamber (GC) above the reduced eighth sternum (VlllStn). 



When the seventh segment is removed there are exposed dorsally 

 the narrow eighth and ninth terga (fig. 24 B, VI I IT, IXT), though 

 the ninth tergum is mostly concealed beneath the eighth. The eighth 

 tergum is somewhat widened laterally, where on each side it forms a 

 sharp marginal ridge as do the preceding terga, and it is then deflected 

 in a small paratergal sclerite {pt) enclosing the eighth spiracle. From 

 the paratergite a fold of the integument extends downward and mesally 

 to the lateral arms of the eighth sternum ( VlllStn). A lateral tergo- 

 sternal muscle of the eighth segment lies just within the fold uniting 

 the tergum with the sternum. 



The sternum of the eighth segment is the sclerotization in the wall 

 of a short fold produced posteriorly from the anterior wall of the 

 vestibulum (figs. 23, 24 B, VlllStn). At the margin of the fold the 

 sternum is reflected dorsally and anteriorly on the dorsal wall of the 

 fold. The fold itself, therefore, is the venter of the eighth segment, 

 and its reflected dorsal wall forms the floor of the genital chamber 

 (fig. 23, GC). Upon the latter is situated the gonopore (Gpr), a 

 long, narrow, median opening (fig. 24 C, Gpr). In Blatta the floor of 

 the genital chamber contains four sclerites composing the eighth 

 sternum; two are small median plates (C, a, a) lying at the sides of 

 the gonopore, and two are large lateral plates {h,b) produced upward 

 on the sides as a pair of arms on which the tergo-sternal muscles of 

 the eighth segment are attached (B). This group of sclerites asso- 

 ciated with the gonopore is termed the " vaginal plate " by Vogel 

 (1925). The view of the genital parts given at C of figure 24 shows 

 the roof of the genital chamber and vestibulum, together with the 

 ovipositor, as seen from below ; but the floor of the genital chamber 

 is turned forward (as indicated by the arrows) along the transverse 

 line {x-x) at its anterior end. 



The roof of the genital chamber contains two large, irregularly oval 

 lateral sclerites (fig. 24 C, c, c) and a median sclerite (d). These 

 plates must be secondary sclerotizations between the eighth and ninth 



