82 PARTIAL ORISMOLOGY. 



consider as the analogue of the posterior wing of the scapula (see 

 PL XII. No. 1, f. 1 and 2, d; No. 2, f. 2, d). In the Diptera, this 

 scale appears as a mere protuberance (PL XIV. No. 1, d) in front of 

 the base of the wings ; thus also, by reason of its smallness in many of 

 the Hymenoptera (punclum callosum ante alas of Fabricius) ; but in 

 these it is always a separate piece. That which has been called the 

 SHOULDERS (humeri) in other Diptera, for example, in Myopa, is 

 certainly erroneous, for it is the analogue of the collar e of the Hyme- 

 noptera, and the same as our pronotum (PL XIV. No. 2, A). In all 

 the apterous genera, as well as in all those orders which display a closer 

 union of the several pieces of the thorax, the scapulae are not either to be 

 recognised as distinct pieces. In the Coleoptera and Orthoptera they 

 are never wanting ; but their separation into two parts, which we have 

 called their wings, is not always apparent. 



The third piece, the MESOSTERNUM (peristethium of Kirby and 

 Spence), is, as well as the scapulae, divided into two parts ; but here 

 they are equal. It is directly opposite to the mesonoium, upon the 

 underside of the thoracic case, and includes one-half of the acetabula of 

 the intermediate legs. It is distinctly observed in all the orders; in 

 many (Diptera, Hemiptera) it is not separated from the other pieces 

 by clearly defined limits, but merely indicated by furrows ; in others 

 (the Hymenoptera), it attains considerable size (PL XII. No. 2, f. 2 

 and 3, E, E), and in these extends upwards upon the sides of the 

 thoracic case, as high as the articulation of the superior wings. In the 

 Coleoptera and Orthoptera, which display considerable resemblance in 

 the conformation of their thorax, it is small, and frequently appears 

 but as a small prominent ridge between the intermediate legs (Hydro- 

 philus, GryllotaJpa, PL IX. No. 1, f. 8, E) ; in the former it is 

 sometimes even excavated for the reception of the dagger-shaped 

 process of the prosternum (Elater, Buprestis, PL IX. No. 3, f. 5, E ; 

 Dyticus, PL IX. No. 2, f. 8). This sternum is separated into two 

 equal halves by a central longitudinal division, which, however, is but 

 little apparent upon its superficies, and can be discovered only upon a 

 close inspection (Buprestis, Dyticus, &c.). 



78. 



The third and last segment of the thorax, the METATHORAX, resem- 

 bles the second, in being of a more united structure than the first, 



