THORAX : MESOTHORAX. 271 



branaceous wings, the mesoscutellum is not so conspicuous 

 an organ. 



The upper surface of the mesothorax is very variable in its 

 consistence, according to the degree of exposure to which it 

 is subject. Thus in the beetles, where it is almost entirely 

 covered by the prothoracic shield, or by the base of the 

 wing-covers, it is leathery or horny, with the exception of the 

 exposed mesoscutellum. If, on the contrary, it is naked, 

 as in the Hymenoptera, Diptera, &c., it is more solid in its con- 

 struction. In the Diptera, the praescutum and scutum of the 

 mesothorax are soldered together (see fig. 126, a 2, b 2), 

 forming the larger part of the upper surface of the thorax ; 

 the scutellum (c 2) is also distinct. In the Lepidoptera the 

 prajscutum is also small, but the scutum (dorsulum, Kirby 

 and Spence) very large and distinct. In the Hemiptera, as 

 in the Coleoptera, the praescutum and scutum are covered by 

 the pronotum. In the Hymenoptera the scutum and scutel- 

 lum are similar to those of the Diptera. 



The under surface, or the mesosternum, is generally horny, 

 and extends between the middle legs, sometimes, as in some 

 Coleoptera (Elaterida), having an impression to receive the 

 spine of the prosternum ; at other times, as in the Cetonia, 

 the mesosternum itself is produced into a spine extending 

 between the anterior legs. 



On each side of the mesosternum extend the epimera and 

 episterna of the mesothorax, the former being termed 

 scapularia by Kirby and Spence ; they are generally of 

 small size, except in a few instances, such, for instance, as 

 the Cetoniidce, in which the former are very conspicuous, 

 forming the horny plate intervening on each side between 

 the shoulder of the elytra and the posterior angles of the 

 pronotum. 



In addition to the above pieces, the paraptera, or tegulac, 

 being the small scales at the base of the upper wings (see 



