476 



ARTICULATED ANIMALS. 



the teguments themselves, each of which bears a breathing pore, so that the sides of 

 the abdomen exhibit a longitudinal series of small pieces, or each segment is, as it were, 

 divided into four. Other pieces, also corneous, occupy the lower sides of the meso- 

 thorax and metathorax, immediately beneath the insertion of the elytra and wings, 

 which are supported by another piece, placed longitudinally. The relations of these 

 parts, the size and form of the first joint of the coxa?, or haunches, the manner in which 

 they articulate with the semi-ring to which they are attached, and the extent and 

 direction of this variable semi-ring, furnish the thorax, considered in this respect, with 

 a combination of characters which is very serviceable in a systematic point of view. 

 Some naturalists, especially Knoch, had already made use of them, but without any 

 determined principle, and with arbitrary names. It was, however, necessary to study 

 the composition of the thorax carefully, in all the classes of insects — a task commenced 

 by the late Lachat, and followed up by M. Victor Audouin, who presented a memoir 

 on this subject to the Academie des Sciences. It is, however, only known to us by 

 the general sketch of it given by Cuvier in his Report*, and by the extract published 

 by its author in the article Insect in the Dictionnaire Classique d'Hist. Nat. To 

 adopt this nomenclature, and give it a general application, we must wait for this memoir 

 and its illustrative figures ; but in practice, the denominations already introduced will 

 suffice. Another memoir, upon the same subject, by M. Chabrier, with admirable 

 figures, and one by the elder Jurine upon the wings of the Hymenoptera, must also be 

 mentioned. 



As insects inhabit all kinds of situations, they have all the kinds of locomotive organs : 

 namely, wings and legs, which last, in many species, are used as oars. The wings are 

 membranous, dry, elastic, generally transparent, pieces attached to the sides of the back 

 of the thorax ; the anterior pair, when there are four, or when they are the only pair, 

 being upon the mesothorax, and the posterior pair upon the following segment, or 

 metathorax. They are composed of two membranes applied upon each other, and tra- 

 versed, in various directions, by more or less numerous nervures, which are so many 

 trachean tubes, forming sometimes a network, and sometimes simply veined. The elder 

 Jurine has advantageously employed the disposition and crossing of these nervures in 

 systematic arrangement. The Dragon-flies, Bees, Wasps, Butterflies, &c, have four 

 wings ; but those of Butterflies are covered with small scales, which at first sight re- 

 semble dust, and which give these insects the colours with which they are ornamented. 

 They easily come off on being touched by the finger, and the portion of the wing from 

 which they have been taken is transparent. With the microscope, these scales appear 

 of varied figures, and are implanted upon the wing by means of a footstalk, and 

 arranged regularly in rows like the tiles of a roof. In front of the fore-wings of these 

 insects are a pair of pterygoda (a kind of epaulettes), which extend backwards along 

 a part of the back, upon which they are applied. In certain insects, the wings remain 



• [A long note is here given in the second edition, containing the 

 details uf M. Audouin's researches. I can, however, only introduce 

 the following slight abridgment : — The trunk, or thorax, is always 

 typically divisible, on the outside, into three segments, each bearing 

 a pair of feet, — namely, the prothorax, mesothorax (bearing the fore 

 wings), and metathorax (bearing the hind wings). Each segment is 

 composed of four parts: one inferior, two lateral (these three forming 

 the breast), and one dorsal, forming the back. The inferior part is 

 the sternum; the lateral pieces, or flanks, are each divisible into three 

 principal pieces ; one (the episternuni) attached to the sternum, 

 another (the epimeron), articulating with the coxa. Another small 

 piece (the trochantine) assists in the union of the epimeron and coxa, 



whilst the third piece of the flank is placed, in the meso- and meta- 

 thorax, beneath the wing, and is called the hypoptera, since changed 

 by Audouin to paraptera. The dorsal part, or tergum, is divided into 

 four pieces, named, from their position in each segment, the prai- 

 scutum, scutum, scutellum, and postscutellum : the first of which is 

 often, and the last nearly always, internal. Thus the thorax is divi- 

 sible into thirty-three principal pieces, or forty-three, including the 

 hypoptera. The epimera had been previously called scapula?, and 

 parapleural, by Knoch. The posterior coxa of the Coleoptera, forming 

 a transverse plate, is his mgerium. Mr. M'Leay has subsequently pub- 

 lished an elaborate memoir upon the structure of the thorax in the 

 Zoological Journal.] 



