80 PARTIAL ORISMOLOGY. 



insects, from the two pieces being united posteriorly, it appears as a 

 small triangle* beneath the cavity where the abdomen is affixed (PI. XL 

 No. 3, f. 3, j). In the Hymenoptera, Lepidoptera, Diptera, and 

 Hemiptera, the pleurae and parapleurse are not distinctly separated, 

 but form a single, undivided pleura, which often, besides, is strictly 

 united with either the metanotum or metasternum, or indeed with both 

 together. 



The PARAPLEURJE (PI. IX., &c. H, H) of the Coleoptera, as well as 

 of the other orders in which it is distinctly found, lies between the meta- 

 sternum and the pleura. In general, they are larger than the latter, 

 lie nearer the under side of the body, and adapt themselves in shape to 

 the space left by the other plates. They are very frequently quadrate 

 (PL XI. No. 1, f. 6, H; No. 2, f. 10), with sometimes parallel, and 

 sometimes diverging sides (PI. IX. No. 3, f. 6, H) ; in other cases, three- 

 sided (PI. IX. No. 2, f. 8, H) ; and very large and trapezoida lin Gryl- 

 lotalpa (PI. XL No. 1, f. 8, H), as well as \nLibellula (No. 3, f.2, H). 

 In these they are prolonged posteriorly, make a bend at the angle of 

 the thorax, and in the centre of the metasternum they unite in one 

 piece (PL XL No. 3, f. 2 and 3, H). In the other orders, the pleurae 

 and parapleurse are not separated, but form one single plate. In the 

 Diptera peculiar interest attaches to it, from the remarkable halteres 

 being seated there. They originate frequently in a stalk (stipes], as fine 

 as a hair, from the anterior margin of the pleurae, and shortly terminate 

 in sometimes a round, and at others a compressed knob (capitulum). 

 They frequently stand quite free, and are then called NAKED (halteres 

 nudi), or else they are covered by one or two delicate SCALES (squama}, 

 which are attached to the mesothorax, and extend from its margin 

 upwards to the scutellum, and are doubtlessly analogous to the previ- 

 ously described frenum of the other orders. We have not yet attained 

 any very distinct idea of the import of the halteres ; but this is not the 

 place to introduce an investigation of the subject ; we refer to the 

 proper place, in the second and third divisions, for much that applies 

 to it. 



* Without this somewhat forced view, it would be scarcely possible to explain the 

 construction of the thorax in the Libellula. We must imagine the feet to be drawn 

 forwards, whilst the back and the wings project posteriorly, whereby the parapleurae are 

 advanced in front of the pleunc, and these united posteriorly into one piece. 



