THE HORNY SKELETON. 243 



of the ball out of the socket, as far as the membrane admits of 

 extension. We find thus united the joints of the antennae, palpi, and 

 tarsi, the head with the thorax, and the prothorax with the mesothorax, 

 in those insects which have a moveable prothorax. At the neck, or the 

 connecting membrane of the head with the thorax, we find, besides, in 

 the Coleoptera, two bean-shaped horny plates (pieces jugulaires of 

 Straus), upon which the occiput moves. These plates, which might 

 be called throat plates (jugularia}, lie transversely in the posterior 

 portion of the membrane which spans the large aperture of the 

 prothorax like a drum-head, and serve for the insertion of several 

 small thin muscles, and, among others, to the two which originate 

 from the central point of the internal metathoracic process which 

 passes through the cavity of the thorax. Their true function is 

 doubtlessly to retain the membrane of the neck distended, and to offer 

 to the occiput a smooth surface, upon which it may turn with facility. 

 In black or dark beetles it is of the colour of the exterior integument 

 (tlydropliilus piceux, Oryctes nasicornis), and is therefore very per- 

 ceptible when the head has been removed from its articulating 

 cavity. In Dyticus I likewise found similar plates between the meso- 

 and meta-notum. A small horny piece, similar in function, lies also in 

 the membrane between the coxae and the sternum in the four anterior 

 legs. It is properly a process of the joint become free, and which, in 

 the intermediate legs, in which the motion is less, stands in closer 

 connection with the coxae. Audouin calls it trochantinus. I have 

 been able to find this piece only in Dyticus ; it exists also in 

 Melolontha, according to Straus, who calls it rotule. 



168. 



STRUCTURE OF THE WINGS. 



We have already, in a preceding division, sufficiently described the 

 formal differences of the WINGS and ELYTRA, as well as of the legs, 

 to complete which we have but to give here a detailed explanation of 

 their peculiar structure. In the description above, we have already 

 mentioned that they are bags formed of a simple membrane, in which 

 horny ribs are distributed. This simple membrane is nothing else 

 than the epidermis, which, proceeding from both sides of the thorax, 

 forms the wings. This is most distinctly seen in those wings which 

 have a broad base, as in the Coleoptera, Orfhoptera, &c., in which we 



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