392 Mr. Bennett on the Anatom?/ of the Thorax 



is termed Prothorax ; the second Mesothorax ; and the third 

 Metathorax. Each of these is again distinguished into its superior 

 or dorsal portion, and its inferior or pectoral portion ; the pectoral 

 portions of the two posterior segments being termed collectively 

 the pectoral concha. 



Essentially connected as these segments are with the organs of 

 flight, the variations which occtir in these latter in the several 

 orders of insects, are accompanied with corresponding differences 

 in the portions of the thorax to which the wings are attached, and 

 the diversity of appearance which has hence arisen, has fre- 

 quently led to the error of appropriating a term to designate one 

 portion of the body in one order, which is applied in another 

 order to an entirely different part ; while on the contrary, two 

 terms have been employed to point out one and the same part, 

 occurring under different forms in two of the orders. These errors 

 which have arisen chiefly from the absence of general views on the 

 subject, will be readily avoided by referring to the analogous 

 portions of other insects, and tracing through the several orders 

 the nature and extent of the variations which are induced by their 

 respective habits. 



In the Coleoptera, the Orthoptera, and the Hemiptera, the 

 Prothorax is remarkable for its size, and is indeed the only part 

 to which the name of thorax would be applied by the superficial 

 observer, the other segments being almost entirely hidden under 

 the elytra and wings. It is formed, in almost the whole of the 

 Coleoptera, of a complete ring which is very solid and consists of a 

 single piece, or of two pieces at most, so closely united as to seem 

 soldered together in such a manner as to be incapable of the slight- 

 est motion upon each other. In the Neuroptera it is composed of 

 two pieces ; which in the Hymenoptera, tjtie Lepidoptera, and the 

 Diptcra, are so very distinct as to be almost independent of each 

 other; the one superior, which is sometimes soldered to the 

 Mesothorax, and the other inferior or sternal, which is again 

 subdivided into two other portions, one of which is anterior and 

 the other posterior. The superior portion or collar, forms, in the 

 Bombi, Vespae, and Apes, a moveable ring of a single piece which 



