186 PROC. ENT. SQC. WASH., VOL. 23, NO. 8, NOVEMBER, 1921 



"protergite" (metaprescutum) and "mesotergite" (meta- 

 scutum). The writer is uncertain as to what the real signifi- 

 cance of this condition may be. There is room for considerable 

 speculation but inasmuch as it does not absolutely disprove the 

 homologies he suggests and since these homologies are founded 

 upon observations on metamorphosis he has refrained from dis- 

 cussing the situation. 



Snodgrass dismisses the derivation of the postscutellum from 

 a succeeding segment on the ground that it is "most frequently " 

 "continuous laterally with the epimerum" although he states 

 that, "often there is a line between the two and sometimes they 

 are only articulated or merely contiguous." He derives the 

 postscutellum as a "secondary tergal chitinization in the dorsal 

 membrance behind the notum," and the following quotations 2 

 from his 1910 paper give his views in brief on the origin of this 

 plate and the phragma: 



P. 45, 5th line: 



"The posterior transverse postalar sclerite of the mesotergum and the meta- 

 tergum (figs. 1, 4, and 5 PN) developed best in those segments that have the 

 wings best developed as organs of flight, though not present in either segment of 

 the Isoptera. It is absent in the mesothorax of Orthoptera, Euplexoptera, and 

 Coleoptera, and is greatly reduced or absent in the metathorax of species having 

 the hind wings reduced. That of the metathorax is generally fused with the 

 first abdominal tergum in Orthoptera^ Euplexoptera, and Hymenoptera. The 

 postnotum is ordinarily called the 'postscutellum' since it lies immediately 

 behind the scutellum of the notum. However, it is not one of the divisions of 

 the notum, since it is formed independently as a secondary tergal chitinization 

 in the dorsal membrane behind the notum." 



P. 45, 39th line speaking of phragmas: 



"The first, when present, is always fused with the front edge of the mesonotum. 

 The second is likewise fused with the front of the metanotum in Orthoptera, 

 Euplexoptera and Coleoptera, but when present in the other orders it is con- 

 nected with the postnotum of the mesotergum. The third is always connected 

 with the metapostnotum even when this plate is fused with the first abdominal 

 tergum. " 



C. W. Woodworth 3 in his review of three papers by R. E. 

 Snodgrass recognizes the significance of the muscular and 

 morphological conditions in the adult insects in the following 

 statements: 



"The interpretation of the origin of the postscutellum or pseudonotum, as 

 he (Snodgrass) calls it, was suggested by myself in the paper previously referred 



'"The Thorax of Insects and the Articulation of the Wings," p. 523. 

 2 Snodgrass, R. E., "The Thorax of the Hymenoptera," Proc. U. S. Nat. 

 Mus., 1910, Vol. 39, pp. 37-91. 

 "Science, Vol. XXX, No. 764, Aug. 20, 1909, pp. 243-244. 



