580 EXTERNAL ANATOMY OF INSECTS. 



tasternal point between their hind-legs. In the remaining 

 Orders there is no metasternum, or no remarkable one, 

 except in one singular Hymenopterous genus, Evania, the 

 parasite of the Blattce a , in which there is a forked pos- 

 terior process of the mesostethium with recurved points. 



1 7. Opercula b . By this term I distinguish those 

 plates, before largely described c , which cover the drums 

 of male Tettigonice F. ; and likewise those called also by 

 the same name by M. Chabrier d , which cover, in many 

 cases, the vocal apparatus of the trunk of insects : those 

 of Melolontha vulgaris he describes as situated below the 

 wings, and between the two segments of the alitrunlc e ; 

 and if you take this insect and remove the elytra, the 

 mesothorax and scapulars, under the latter and below the 

 wing you will find an oval convex plate, which is pro- 

 bably the part he is speaking of; — but it is better exem- 

 plified, I think, in the common Dytiscus marginalis, in 

 which it is very distinct as a convex subtriangular plate 

 connected with the metathorax by membranous ligament, 

 covering a land of pouch, and appearing to open and 

 shut at the vertex f . 



I must here observe, with regard to the Aptera and 

 Arachnida, that the trunk in them is much more simple 

 than in those insects that are furnished with wines. In 

 the hexapods, in the former Orders, though there are 



a The history of this parasite has been traced by Dr. Reid j but 

 alas ! this learned and acute observer of nature did not live to give 

 his discoveries to the world: it is hoped, however, they will not be 

 lost, being in most able hands. 



b Plate VIII. Fig. 18. and XXII. Fig. 13. c f. 



° VoL - IL P- 405 - d Surle Voldes Ins. c. i. 459. 



e Ibid. 457-. * p LATE xxil. Fig. 13. c f. 



