74 PARTIAL ORISMOLOGY* 



follows the middle piece, arid which extends to the end of the meta- 

 thorax ; pleurce (the sides), the space between the scapular ia and the 

 insertion of the wings. The under side of the posterior division of the 

 alitruncus they call the post-pectus ; it is divided into the mesostethium, 

 the central piece between the intermediate and posterior legs (Knoch's 

 acetabulum} ; the parapleurce, the lateral pieces on each side of the 

 mesostethium ; the metasternutn, the elevated central ridge of the 

 mesostethium ; the post-furca, the internal descending process of the 

 metathorax and the opercula, which cover the spiracles of the meta- 

 thorax. 



To whom is not the elaborately strained nature of these definitions 

 apparent ? To call the anterior legs, hands, and that portion of the 

 body upon which they are placed, the manitrunk, is certainly a very 

 forced endeavour to find analogies. The upper surface also cannot be 

 called thorax, and the under side pectus ; for pectus universally means 

 the anterior portion of the thorax, and its posterior or upper surface is 

 called dorsum, or back. It is also erroneous to consider the collars as 

 a distinct part, as it is evidently what they call thorax in the Coleo- 

 ptera. Notwithstanding their assertions to the contrary, they will never 

 be able to convince us of it. Wheresoever a part is not immediately 

 recognised, it displays no art to give it a peculiar name ; but, on the 

 contrary, it shows much to prove, by a careful study, the relations of 

 the several parts in the different orders, and the variations they are 

 subjected to. This has been the problem which the following sections, 

 containing a description of the thorax, seek to solve. 



74. 



The thorax of insects consists of three corneous segments, from each 

 of which a pair of legs originate ; and the two posterior, or only the 

 intermediate one, always bear besides a pair of wings. We distinguish 

 these segments as the PROTHORAX, MESOTHORAX, and METATHORAX *. 

 In its most simple conformation, each of these segments is wholly 



* Ch. L. Nitzsch, \vho first proposed these three names for the three segments of the 

 thorax, wrote protothorax; but as he himself called the^third segment metathorax. forming 

 it consequently of a preposition and a substantive, the analogously compounded name of 

 the first segment proposed by Kirby and Spence is, therefore, better than the former. 

 Had Nitzsch compounded all the three names of ordinal numerals, his would have had 

 the preference, as being the first ; in consequence, therefore, those proposed by Kirby and 

 and Spence take precedence. 



