1919] Walker: Structure of Orthopteroid Insects 281 



We may take as an example of the family the common field 

 cricket {Gryllus assimilis Fabr.) 



In this species (Figs. 11-15) the eighth and ninth tergites 

 are very short in the mid-dorsal line, but the ninth expands 

 considerably on the sides and extends farther ventrad than 

 the others. The seventh sternum is very large, but is not 

 produced caudad as a free flap, while the eighth sternum 

 forms a small subgenital plate, similar to that of the Tetti- 

 goniidas. The eighth spiracle occupies the pleural membrane 

 close to the tergal margin. The tenth tergite is laterally very 

 short, but is dorsally longer and fused with the supra-anal 

 plate, though the line of fusion is visible. The paraprocts are 

 larger and more heavily chitinized than is usual in the Tetti- 

 goniidae. The cerci are long, flexible and tapering, with numerous 

 hairs and sensill^, being very similar to those of Ceuthophilus, 

 though larger. 



The valvifer is very large and is produced under cover of the 

 subgenital plate into a strong process, which probably represents 

 a part of the basivalvula. Its inner surface is without strong 

 marginal ridges, but bears a stout process or apodeme, directed 

 ento-caudo-dorsad. Its antero-dorsal angle is connected, as 

 usual, with the ninth tergal apodeme, which is well developed. 

 There is also a similar but weaker eighth tergal apodeme. 



The ventral valvulae are without distinct basivalvulae, but 

 these are represented by a well-defined unchitinized area, 

 covered by the subgenital plate, and probably also by the 

 ventral processes of the valvifers. 



The dorsal valvulce are peculiar in the sudden expansion of 

 their bases, this part forming part of the sternal surface rather 

 than the valves themselves. Between these bases and partly 

 fused with them is the relatively large superior intervalvula. 

 Like that of Conocephalus, its lower part is deeply depressed 

 and it is also similarly produced cephalad into a thin median 

 apodeme. The superior and inferior apophyses are well 

 developed and the latter are connected by a transverse bar, 

 which represents the inferior intervalvula. 



The shafts of the dorsal and ventral valvulae fit closely 

 together by a tongue-and-groove joint and their enlarged 

 apices are locked together by a peculiar structure, consisting 

 of a projection from the dorsal valvula, which fits into a socket 

 in the ventral valvula. 



