576 EXTERNAL ANATOMY OF INSERTS. 



tervenes between the postdorsolum and its adjuncts and 

 the abdomen, and which bears a spiracle on each side, 

 is the metapnystega a . This part is often remarkable, 

 not only for its size, but for the elevated ridges that 

 traverse it, as in Ichneumon, Chlorion, &c. In the last 

 genus it is of a pyramidal shape, with the anterior part 

 horizontal and the posterior vertical; it is altogether 

 vertical in Vespa, Apis, &c. Amongst the Diptera, in Ti- 

 pula it is nearly horizontal, and shaped like a cushion ; 

 but in general in this Order it is vertical, and concealed 

 under the postdorsolum^ . 



We are now to consider the parts that constitute the 

 postpectus or under-side of the metathorax, and which 

 bears the posterior pair of legs. 



14. Mesostethium . This part in Coleoptera is termi- 

 nated anteriorly by the peristethium, scapulars, and me- 

 sosternum, laterally by the parapleurce d , and behind by 

 the coxae of the posterior legs e , which generally are in- 

 serted transversely between it and the abdomen. It is 

 commonly very wide ; but in Dytiscus L., Carabus L., 

 &c.j in which the coxce and parapleurce are dilated, it is 

 proportionally reduced : its length is regulated by the 

 distance of the intermediate and posterior legs ; where 

 these are far asunder, as in the rose-scented Capricorn 

 {Callichroma moschatum), &c. it is long : but where they 

 are near each other, as in the Scarabceidce MacLeay, it 

 is short ; its width, however, generally exceeds its length. 

 In shape it is generally subquadrangular f , though some- 



a Plate IX. Fig. 11. k" . b j bid# FlG _ 20 k". 



c Plates VIII. IX. y . d Plate VIII. Fig. 4. z. 



* Ibid. p". f i bid- y_ 



