MANDIBLES. 251 



are composed of a single piece, and are destitute of any ap- 

 pendage. In some of the Brachelytra (especially the species 

 ordinarily termed the devil's coach-horse, fig. 98) their inner 

 surface is, however, furnished with a small moveable exarti- 

 culate process, as is also the case in Passalus and Hydrous. 

 By Linnaeus they were termed maxilla. In beetles these 

 organs are generally of large size, and of a horny substance. 

 The large and powerful instruments with which the head of 

 the stag-beetle is armed are the mandibles immensely deve- 

 loped; but these organs, like many others, exhibit great 

 variations, according to the sexes. In the last-named insect, 

 for instance, the jaws of the females are so short that this 

 sex was long regarded as a distinct species. They are usually 

 symmetrical, but in many cases are dissimilar in form, and 

 more particularly in the structure of the teeth, with which 

 they are commonly furnished. In some of the lamellicorn 

 beetles, the internal base of these organs is dilated into a 

 broad and flattened square plate, having numerous transverse 

 ridges, serving for the purpose of bruising the leaves upon 

 which these insects feed (fig. 9/). In some beetles also, 

 which subsist upon the juices of flowers, or upon the flowing 

 sap of wounded trees, &c., the jaws are of a membranous 

 structure, and quite unfitted for mastication. In the Hyme- 

 noptera also, the jaws, although of the ordinary form, cannot, 

 in many cases, be regarded as masticating organs, but ap- 

 pear solely to be employed in the construction or the provi- 

 sioning of the nest. In the Lepidoptera they are very mi- 

 nute, membranous, and triangular, and placed on each side 

 of the labrum. In the Hemiptera they are very long, slen- 

 der, and employed in conjunction with the maxilla as lan- 

 cets. They have also the same character in the Diptera; 

 but here they are often entirely wanting. They are, how- 

 ever, particularly distinct in the gnats and gadflies (Tabanid<e, 

 fig. 88, m). 



