EXTERNAL ANATOMY OF INSECTS. 573 



and proceeds towards the middle of the basal margin of 

 the wing. In the Petalocerous beetles the part in ques- 

 tion is usually more or less hairy ; but in many others, 

 as the rose-scented Capricorn (Callichroma moscliatum\ 

 &c. it is naked. At its side you will commonly observe 

 several plates and tendons (osselets Chabr.) connected 

 inter se and with the base of the wing by elastic liga- 

 ments, which are calculated to facilitate the play of those 

 organs. In the Orthoptera, Neuroptera, and Homopte- 

 rous Hemiptera, the postfrcenum does not differ mate- 

 rially from Xhefrcenum a . In the Heteropterous section 

 of the last Order it is usually a transverse ridge termi- 

 nating the postdorsolum, with a bifurcation where it 

 unites with the wing ; but in Tetyra F. (at least so it is 

 in Tetyra signata,) it is a nearly vertical piece, marked in 

 the centre with an infinity of very minute folds, which 

 probably by their alternate tension and relaxation let 

 out and pull in the wings. Amongst the Lepidoptera it 

 is not remarkable. In the Hymenoptera Order it is 

 mostly represented, I think, by a double ridge or fork, 

 sometimes however obsolete, but very conspicuous in the 

 saw-flies, which laterally terminates the postdorsolum ; 

 the upper branch, usually the thickest, going to the an- 

 terior part of the base of the underwing, and the lower 

 one to the posterior. You may observe something simi- 

 lar in the crane-flies {Tipula Latr.) and Asilidce. A 

 tendon proceeding from the point of the postscutellum 

 forms a fork near its end, the upper branch of which 

 connects with the anterior and the lower with the poste- 

 rior valve of the winglet; the structure is a little, but not 

 essentially, different in other Diptera. 



» Plate VIII. Fig. 12, 16.; and Plate IX. Fig. 7. v. 



