12 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 85 



lateral groove of the abdomen as the " sternopleural suture," he 

 takes the paratergal areas to be the abdominal pleura. 



The abdominal terga. — The dorsal sclerotizations of the abdomen 

 in general take the form of simple tergal plates characteristic of any 

 region of the body in which a secondary segmentation has been 

 established. Each tergum presents anteriorly a submarginal or often 

 marginal internal ridge, the antecosta (fig. 2 F, G, Ac), on which 

 the principal longitudinal muscles usually have their attachments. 

 The antecostal suture (F, acs) is generally but faintly marked, and 

 the precosta (F, G, Pc) varies from a scarcely perceptible marginal 

 rim to a wide flange extending a considerable distance anterior to the 

 muscle attachments (G, Pc). Apodemal processes are frequently ex- 

 tended from the anterior margins of the terga. From the antecosta 

 of the first abdominal tergum there is commonly developed a pair of 

 phragmatal lobes, and the precostal part of this tergum, together 

 with the antecosta and the phragma, may be separated from the rest 

 of the tergal plate to form a so-called postnotal or postscutellar plate 

 of the metathorax. Otherwise the abdominal terga usually preserve 

 their structural unity. The postcostal areas of the abdominal terga are 

 seldom marked by sutural lines in adult or nymphal insects, and where 

 such lines do occur they can not be supposed to have any homology 

 with the sutures of a wing-bearing thoracic tergum, which adapt the 

 latter to its function in the wing mechanism. 



The dorsal regions of the abdominal segments of soft-bodied holo- 

 metabolous larvae are usually divided transversely by impressed lines 

 or by strongly pronounced topographical features. The dorsal areas 

 thus formed are evidentl}^ mere adaptations to the contractile move- 

 ments of the larvae and have no morphological significance. That 

 the external body features of cruciform and vermiform larvae are 

 secondary larval characters is evident from the structure of the head, 

 which shows that such larvae are lateral derivatives from highly 

 evolved adult forms representing the immediate ancestors of the 

 order. 



The abdouiinal slerna.-^T\\Q definitive sternal plates of the abdomen 

 are in general similar to the tergal plates, each being a continuously 

 sclerotized area of the ventral integument of its segment, always 

 including the primary intersegmental area anterior to the somite, 

 corresponding with the intersternites, or spinisternites, of the thoracic 

 region. The antecostae may be coincident with the anterior margins 

 of the sternal plates, or set well back from the margins (fig. 2 F, Ac) 

 with distinct precostal regions before them. In the Japygidae a short 

 anterior division of each abdominal sternum is separated by a mem- 



