92 PARTIAL ORISMOLOGY. 



deficient, more frequently only the posterior pair : thus, in all the 

 Diptera, some Cimices and many Coleoptera, but in the majority of 

 cases there are four distinct wings present. The deficiency of the first 

 pair has never been observed. 



Their situation is more certain than their number, for wherever we 

 find wings, they are attached to the second and third segments of the 

 thorax, and, indeed, at its superior exterior dorsal edges, close to where 

 the dorsal and lateral plates adjoin. If we find no wings here, we can 

 speedily convince ourselves whether the insect does not possess them, 

 or whether it has lost them by some casualty, which is not of unfre- 

 quent occurrence. We speedily detect such a mutilation by the 

 presence of the joint sockets and a portion of the wings. Apterous 

 insects entirely want the sockets. 



Before we proceed to the consideration of the form of the wings, we 

 must remind ourselves of the differences indicated in the preceding 

 table, as they exercise an important influence upon the form of the 

 wing. The horny or pergamentaceous anterior wings, namely, differ 

 so considerably in their whole structure from the membranous poste- 

 rior wings, that they have been very justly considered as different 

 organs, and have been called the WING CASES (Elytra). The whilst 

 the beetle, or any other insect which possesses elytra, reposes, they lie 

 parallel beside each other upon the back and abdomen, and thus conceal 

 not only the posterior wings, but also very generally the whole abdo- 

 dem. It is from this function that they derive their name. 



We distinguish in the elytra their BASE (basis), the part by which 

 they are attached to the thorax, and the opposite extremity, the APEX : 

 then the MARGINS and the inner ones, which lie contiguous, and which 

 we call the suture. Should the posterior wings be wanting, the union 

 of the elytra is generally so strict, that it requires great force to sepa- 

 rate them ; such elytra are called CONNATE (Elytra connata). The 

 angles are thus distinguished, the superior exterior one, as shoulder 

 angle (angulus humeralis), the interior one, as the angulus scutel- 

 laris. 



The most usual form of the elytra is the longitudinal extended, we 

 might almost say oblong, did not the exterior bowed margin very 

 generally join the sutural margin, a ta pointed angle, or by its rounding 

 very gradually pass into it. The upper surface is convex, the under 

 concave ; the exterior margin is very generally deflexed, and often 

 forms on the exterior a sharp edge. 



