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Rh observable in particular parts, will be afterwards traced as these orders pass successively under our review. The mesothorax is not always readily recognised by its situation as intermediate between the prothorax and metathorax, for, as above intimated, it frequently appears in direct connection with the head; but it may always be known by supporting the fore-wings and middle pair of legs; its anterior part is sometimes received into a cavity of the prothorax, when the latter is highly developed superiorly, at other times the union between the two is by the edges. So intimately is it soldered behind to the metathorax, that there is frequently no visible suture, but in many instances traces of the union can be detected. According to Burmeister, (whose nomenclature of the parts in question appears to us preferable to that of most authors, on account of its greater uniformity and simplicity,) this section consists of seven pieces, but, as three pairs of these are so closely united that each pair seems to form only one piece, it may be regarded as composed of four principal parts; the first of these, the mesonotum, (corresponding to the dorsolum and scutellum of Kirby and Spence,) forms the dorsal covering of the mesothorax. In many insects it is almost invariably concealed, but in others it is exposed and conspicuous; in such cases its form is usually square, and there is a superficial indication of its consisting of two parts; the one of these, the true back, exactly corresponds to the dorsolum of Kirby, the other is the scutellum, which