NO. 2 THORACIC MECHANISM OF A GRASSHOPPER SNODGRASS 43 



median triangle of the scutellar region (Scl) are confluent in a large 

 shield-shaped area that forms the principal part of the tergal plate. 

 The depressed posterior lateral parts of the scutum (set, set) are cut 

 transversely by the faintly-marked sutures (s, s) of the posteriorly 

 convergent ridges, which are obsolete in the metatergum, though 

 strongly developed on the mesotergum (fig. 22 B, s). The posterior 

 marginal area of the metatergum (fig. 24, Rd), which is a part of the 

 true scutellar region, is sharply inflected (fig. 25, Rd^) and is continu- 

 ous with the greatly extended precosta of the first abdominal segment, 

 which constitutes a postnotal plate of the metathorax (figs. 24, 25, 

 PN,). 



1Mb ^ 



Pc Set. ScL Rd Sct^ Scl 



\ acs ^ — ^— •-' ^^"^ ' 



Fig. 25. — Median longitudinal section of mesotergum, metatergum, and meta- 

 thoracic postnotal plate of Dissosteira, showing the phragmatal lobes of the 

 right side. 



Ac, antecosta; acs, antecostal suture; IT, first abdominal tergum; iMb, 2Mb, 

 secondary intersegmental membranes ; iPh, 2Ph, sPh, first, second, and third 

 phragmata; PN3, postnotal plate of metathorax, or greatly enlarged precosta of 

 first abdorninal tergum ; Rd, posterior reduplication of tergum ; Set, scutum ; 

 Scl, scutellum. 



The lateral margins of the metatergum present the same features as 

 do those of the mesotergum. The posterior angle of each prescutal 

 area projects as a small marginal process (fig. 24, n) which is con- 

 nected with the head of the subcostal wing vein by a ligament-like 

 thickening of the basal wing membrane ; it does not articulate with the 

 vein as in the mesothorax. The anterior notal wing process (ANP) 

 is a flat lobe of the scutum, to which the first axillary (lAx) is closely 

 hinged. Behind the wing process is a deep emargination (Em) of the 

 scutellum, posterior to which is a second lobe (0) articulating with 

 the posterior end of the first axillary. The slender fourth axillary 

 (4Ax) articulates with the extreme posterior angle of the lateral scu- 

 tellar area (set). Each extremity of the posterior marginal fold of 

 the tergum (Rd) gives off into the anal membrane of the wing a long 

 arm (p) that supports the anal veins (fig. 47 B). 



