THE WINGS. 245 



connection of these vessels with the heart, it being well known that 

 blood is found in the entire cavity of the body of insects, and, by each 

 contraction, can be injected into the open ribs of the wings. Chabrier * 

 describes, besides, a bag in the posterior wings of beetles, which lies at 

 their point of flexure, and which is filled with a fluid during flight. 

 The equilibrium is thereby thus supported. He considers in the other 

 orders the stigma analogous in function to this bag. The clammy 

 fluid contained in this stigma is probably merely parenchyma, but even 

 in insects which had been immersed in spirits of wine, I have found a 

 moisture in the bag, but which, without doubt, was introduced from 

 without. 



The connection of the wings with the thorax varies according to the 

 different orders. Broad wings, attached by their entire bases, are found 

 in the Coleoplera, Orthoptera, Dictyoptera, Neuroptera, Hemiptera, 

 and Lepidoptera, consequently in the majority ; wings with pedicles, 

 and attached to the thorax by a narrow base, are found in the 

 Hymenoptera, some of the Neuroptera, and the Diptera. 



The superior wings, or elytra, of the beetles have at their base two 

 short processes, the one of which originates at the inner margin, and 

 the other at the outer margin. Both articulate with two processes at 

 the mesonotum, which originate from it at the anterior part of the 

 lateral margin, and are united to those of the elytra by means of a 

 flexible membrane. In this membrane several free horny pieces are 

 placed, to which the muscles are attached which move the wings. 

 Straus found in Melolontha four such plates, and called them shoulder 

 pieces (\.pre-epauliere, and S.epaulieres). From the posterior margin 

 of the internal process of the joint of the superior wing, a delicate 

 semicircular membrane springs (frenum of Kirby and Spence), which 

 passes over to the similar process upon the mesonotum, and which 

 retains the expanded wing. In Dyticus it is narrower, fringed upon its 

 margin, very broad in Hydrophilus, and in apterous beetles (Carabus) 

 it is wanting. This membrane, which is present in the majority of 

 insects, and which, for example, in Libellula, is the coloured triangle 

 at the posterior margin of the wing, and appears very similarly in the 

 wings of the grasshopper, is so far of importance, that from it the 

 scale behind the wings of the Diptera derive their significance. They 

 are, namely, the frena of the superior wings, Which cannot longer 



* Siir le Vol de* Insectes. Mem. clu Musec, torn, vi viii. 



