1 86 THE INTEGUMENTAL SKELETON OF THE IMAGO. 



the meso- and metathorax, and the mesophragma is situated 

 behind the spiracle and immediately in front of the meta- 

 pleuron. Owing to the great development of the dorsal region 

 of the mesothorax, the dorsal arch of the metathorax is pushed 

 downwards and backwards, and lies on the abdominal surface 

 and lower edge of the post-scutellum, with the halteres between 

 it and the metapleura. 



The post-scutellum of the metathorax of the Cockchafer, the 

 tergum of Straus Durckheim, is very similar to the post- 

 scutellum of the mesothorax of the fly ; and like the latter, 

 is divided into a central shield, two lateral plates and two 

 tympanic bullse, although the latter are feebly developed. 



The great mobility of the scutellum on the post-scutellar 

 region, and the compact union of the latter with the meta- 

 sternum, have led some to regard it as a portion of the meta- 

 thorax; but the relations of the parts amongst themselves, 

 and those of the mesophragma and the halteres show conclu- 

 sively that the post-scutellar region is mesothoracic. 



The Metathorax consists of the metasternum, which has been 

 already described, the metapleura and the post-dorsum. 



The Metapieuron (41 and 42} bears the same relation to the halter that 

 the mesopleuron does to the win, but, like the appendage which it sup- 

 ports, is reduced to very small dimensions. It is in the form of a nearly 

 vertical isosceles triangle, with its apex upwards. 



Its internal surface (Plate VIII., Fig. n) exhibits three well-marked 

 ridges. The central ridge is nearly vertical ; its upper extremity bifurcates 

 and forms a pair of rounded horns, which surround the lower half of the base 

 of the halter. The anterior and posterior ridges are the sutures, in front 

 between the metapleuron and the metasternum, and behind between the 

 posterior edge of the metapleuron and the abdomen. 



The metapleuron is therefore divided, like the pleuron, into two parts 

 the epistermnn and the epimeron of the metathorax. 



The Episternum of the metathorax (42) articulates in front with the 

 metasternum, and below with the posterior coxa ; above with the post- 

 dorsum and halter, and behind with the epimeron. 



The Epimeron of the metathorax (41} articulates below with the posterior 

 coxa ; behind it is united by syndesmosis with the dorsal arch of the first 

 abdominal segment ; above it articulates by its cornu with the halter and 

 post-dorsum ; in front it is united by symphysis with the episternum. 



The Post-dorsum is reduced to the form of a thickened fold, which unites 



