46 



SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 8o 



logically the posterior part of the segment. Only in larval insects is 

 the primary body segmentation (fig. 23 A) found in the thorax, and 

 even here the union of the primitive terga with the chitinized inter- 

 segmental fold may establish a typical secondary segmentation. In 

 the larva of Scarites (fig. 25), the fold between the protergum and 

 the mesotergum is chitinized and united with the latter, forming thus 

 an antecosta of the mesotergum. From the antecosta of each of the 

 wing-bearing segments, and from that of the first abdominal segment 

 there is usually developed a pair of thin chitinous lobes, the two 

 constituting a phragma (fig. 21, Ph), which projects into the cavity 



Pc Psc Ph PR Ac 



\ \ _/ \ / / 



AxC 



Fig. 21. — Diagrammatic structure of a wing-bearing tergum, not including a 

 postnotum. 



A, dorsal; B, ventral. Ac, antecosta; ac, antecosta! suture; ANP, anterior 

 notal wing process; AxC, axillary cord; Aw, prealar process; Em, lateral 

 emargination of tergum; Par, parapsidal ridge; par, parapsidal suture ; Pc, 

 precosta ; Ph, phragma ; PNP, posterior notal wing process ; PR, ridge between 

 prescutum and scutum ; ps, prescuto-scutal suture ; Psc, prescutum ; Rd, posterior 

 reduplication of tergum; Scl, scutellum; Set, scutum; VR,^ ridge between 

 scutum and scutellum ; vs, scuto-scutellar suture ; W, base of wing. 



of the thorax and furnishes an increased surface for the attachment 

 of the dorsal longitudinal muscles. 



The wings are hollow outgrowths from the lateral parts of the 

 dorsum in each segment, between the prealar bridges and the posterior 

 edge of the tergum (fig. 21 A, W). The posterior margins of the 

 wings, therefore, are direct continuations from the posterior fold 

 (Rd) of the tergum. The dorsal wall of each wing is continuous with 

 the lateral margin of the tergum, the ventral wall is reflected into the 

 pleural subalar membrane. The wings become movable by the mem- 

 branization of their bases. The lateral edges of the adult tergum are 

 produced into small lobes to support the dorsal articular elements of 

 the wings ; generally there are two lobes on each side, an anterior 



