COLEOPTERA. 



491 



THE FIFTH ORDER OF INSECTS — 



COLEOPTERA, Linn. (Eleutherata, Fabr.),— 



Have four wings, of which the upper pair is crustaceous, iu the form of scales, horizontal, 

 and meeting [when at rest] along the inner edge by a straight line. They have, likewise, 

 mandibles and maxillae, and the lower wings are folded only transversely, and covered by the 

 other two, which form a kind of case, and which are generally known under the name of elytra. 



These insects [generally known under the English name of Beetles] are the most numerous 

 and the best known of the insect tribes. Their singular forms, the brilliant colours exhibited 

 by many of their species, the size of their bodies, the more solid texture of their teguments, 

 which renders their preservation much more easy, and the numerous advantages to be derived 

 from the investigation of such a variety of forms of their external organs, have merited for 

 them the particular attention of naturalists. 



The head is provided with two antennae of variable form, and of which the number of joints 

 is generally eleven ; two facetted eyes ; no ocelli ; and a mouth composed of an upper lip, two 

 mandibles, mostly of a scaly consistence, two lower jaws (maxillae), each bearing one or two 

 palpi, and a lower lip formed of two pieces, namely, the mentum and the tonguelet {languette), 

 and accompanied by two palpi, generally inserted upon this latter piece ; those of the 

 maxillae, or the outer maxillary palpi (when they bear two), have never more than foiu* joints, 

 whilst those of the lower lip have, ordinarily, only three joints. 



The anterior segment of the trunk, or that which is in front of the wings or elytra, and 

 which is commonly named the corselet [prothorax], and which bears the first pair of feet, 

 and greatly surpasses in extent the two other segments, which are compactly united together, 

 as well as to the base of the abdomen : their under part, or the sternum or breast, serves 

 as a point of attachment to the two other pairs of feet.* The second of these segments [or 

 the mesothorax], upon which is placed the scutellum, is narrower in front, so as to form a 

 short peduncle, which is received into the inner cavity of the first segment [or prothorax], 

 and which serves as a pivot to assist in all its movements. 



The elytra and wings arise upon the lateral and superior margins of the hinder division of 

 the thorax, [or the meso- and metanotum]. The elytra are crustaceous, and in repose are 

 a})plied one against the other in a straight line along the inner margin, or suture, and are 

 always in a horizontal position. In almost every instance they hide the wings, which are 

 large, and folded transversely. Many species are wingless ; but the elytra are always present. 

 The abdomen is sessile, or united to the thorax by its greatest vvulth : it is comjjosed on the 

 outside of six or seven segments ; membranous above, or of a consistence less firm than on 

 the under side. The number of joints on the tarsi varies from three to five.f 



Beetles undergo a complete metamorphosis. The larva resembles a worm, with a scaly head 

 and mouth, analogous in the number and functions of its parts to that of the perfect insect, 

 and also with six legs : some species, however, few in number, are destitute of these appen- 

 dages, or have only simple fleshy tubercles. 



The pupa is inactive, and does not take any nourisliment. The habitation, mode of life, 

 and other habits of these insects, both in their immature and perfect states, vary very much. 

 I have divided this order into /owr sections, after the number of joints of the tarsi. J 



* The mesothorax is always narrow and short, and the metathorax, 

 often of larger size, is lonj^ituditially impressed liown the centre. 



t Judjrinf^ from analogy, the Coleoptera described as montinierous 

 liave probably three joints to tlie tarsi, but of which the two basal 

 joints escape the \iew : this section, as well as the Dimera, have been 

 suppressed in this edition. 



J [The distribalion of the Coleoptera, founded upon the number of 

 joints iu the tarsi, has been objected to by some authors, as it has tlie 

 effect, if rijridly adhered to, of separating certain groups nearly related 

 together : as, for instance, the Pselaphidx (which have only ^-jointed 



tarsi), and the StaphylinidiC, which have 5-joiuted tarsi. Some 



nalu 



varyinif in the sexes. Another objection has been raised to the tarsal 

 system, on the ground, that the so-called Tetramera have, iu effect, 

 5-jointed, instead of 4-jointed tarsi ; and tlie Trimcra, 4-jointed, and 

 not 3-jointcd tarsi, ns those names indicate. But these objections 

 appear to me insuflieient ; due allowances must be made for certain ex- 

 ceptions against every rule ; and the peculiar structure of the tetrame 

 roua or trimerous tarsi, C(|ually merits their retention as distinct groups. 

 Mr. M'Lcay has proposed u classification of the Beetles, founded upon 



