of Heteropterous Insects. 27 



The anomaly in the genus which I propose to notice in 

 this communication, consists in the peculiar structure of the 

 upper wings, (or hemelytra as they have been termed by 

 Messrs. Kirby and Spence, in the Heteropterous insects), of 

 the species of which it is composed. A few general remarks 

 upon the structure and functions of these organs will not be 

 out of place. 



In the order Coleoptera, the upper pair of wings is trans- 

 formed into a pair of corneous cases, generally extending to 

 the extremity of the body, and when unemployed, shutting 

 closely together by a straight suture down the back. Thus 

 united, they become a shield of great strength, defending the 

 posterior pair of wings, which, when at rest, are transversely 

 folded up beneath them, and which, when the insect is on the 

 wing, are its only effective organs of flight. This lower pair 

 of wings is membranous, and distended by corneous air-tubes. 

 In the order Orthoptera, the anterior wings, when at rest, form 

 a shield to the posterior wings, although much less effective 

 than that of the beetles, since they are of a much more coria- 

 ceous texture ; the posterior wings themselves are membran- 

 ous, of a large size, and when at rest, they are longitudinally 

 folded. During flight, both pairs of wings assist in locomo- 

 tion. In the Neuropterous, and some other groups, the pos- 

 terior pair of wings are not defended, when at rest, by the 

 anterior, and they are consequently not folded up, as in the 

 foregoing ; whilst, in the Hymenoptera and Lepidoptera, the 

 anterior wings are larger than the posterior, which are likewise 

 never folded up. In these last tribes, all the wings are mem- 

 branaceous. We thus see, that where the posterior wings 

 take a large share in the act of flight, it is necessary that, being 

 of a larger size, they should be folded up, and defended by 

 more or less powerful wing-cases, while unemployed ; when, 

 on the other hand, the anterior wings take the largest share 

 of active force during flight, the posterior are so much redu- 

 ced, as to require no defence : in other words, where we find 

 large and strong wing-cases or shields, the active organs of 

 flight are membranous, large, and folded up. 



On applying these principles to the Heteropterous insects, 

 (Genera Cimex, Nepa, and Notonecta of Linnaeus), we find 

 that the organization of the wings differs from any of the 

 groups mentioned above, yet their general functions may be 

 most assimilated to those of the Orthoptera. The anterior 

 wings are coriaceous throughout their basal half, and mem- 

 branous throughout their apical portion ; the posterior wings 

 are of a moderate size, and when at rest folded longitudinally, 

 and defended by the hemelytra, which are horizontally shut 



