14 PROCEEDINGS OF THE ACADEMY OF [Jan., 



of Polistes are but portions of the mesothoracic parapsidoscutum. 

 MacLeay's suggestion, that the mesothoracic parapsides are but the 

 prothoracic paraptera( !) pushed back from their original position, 

 must, therefore, be regarded as entirely untenable. 



The parapsidoscutum is very closely connected with the organs of 

 flight; and indeed its caudal portion appears to merge into the mem- 

 branous anal region of the wing. 



Along the sides of the scutum lie a number of small plates which are 

 usually free, but may be more or less fused with one another or with 

 the scutum. Jurine, '20, has described six of these for Hymenoptera, 

 but only three are of particular importance. The first of these is found 

 at the base of the costal region of the wing, and has been termed the 

 antesigmoid by Amans, '85; the second, which Amans terms the 

 "piece quadrilatere" (sigmoid), is situated at the base of the median 

 region of the wing; and the third or dorso-terminal lies at the base of 

 the anal region of the wing. The structure and mechanism of these 

 sclerites has been described in detail by Amans, '85, and Voss, '04, 

 and need not, therefore, be further discussed here. 



In addition to the above-mentioned sclerites, there occur two plates 

 (one at the base of each wing) which have been variously termed 

 squsemula, tegula, paraptera, pterygoda, etc. Of these terms, La- 

 treille's, '20, "pterygodes" or pterygoda appears to have the right of 

 priority, and on this account has been here adopted. In Gryllus, Voss, 

 '04, has described a structure which he terms a " Hautpolster," but does 

 not compare it with other insects. This structure is beyond a doubt 

 homologous with the pterygoda, and bears the characteristic hairs. 

 In the Trichoptera, although still somewhat "Polster"-like, it is more 

 strongly chitinized, and in the Hymenoptera it forms a horny scale, 

 covering the base of the wing. In certain Lepidoptera the pterygoda 

 are greatly developed and are densely beset with hairs. Westwood, 

 '39, has confused these with the patagia of the Lepidoptera, but they 

 are doubtless quite different structures. 



The Scutellum. — Behind the scutal region lies a small, medianly- 

 situated scutellum (fig. 1, N 3 ). In form it may be somewhat semi- 

 circular, oval, shield- or wedge-shaped. In the latter case its anterior 

 end is embedded in the parapsidoscutum. Its posterior margin is 

 usually drawn out into a narrow strip on either side, and is continued 

 in the posterior margin of the anal region of the wing. . This character 

 is frequently very useful in determining the boundaries between the 

 mesoscutellum and.phragma, or to distinguish[the mesoscutellum from 

 the metanotum when these are partially fused . 



