EXTERNAL ANATOMY OF INSECTS. 699 



or tegmina, that part, as was requisite for its protection, 

 is harder than the covered portion. 



ii. Articulation with the trunk. Two distinct modes 

 of this articulation take place : — in the first the abdomen 

 is united to the trunk by the whole diameter of its base, 

 without any appearance of incision ; in the other only a 

 small part of that diameter, with a very visible incision. 

 All the Orders, except the majority of the Hymenoptera 

 and Diptera, and the Araneidce, belong to the Jirst of 

 these sections ; for in all these the aperture by which the 

 abdomen is suspended to the trunk, occupies the whole 

 of the base ; I say suspended, because, though in many 

 cases it inosculates in the posterior cavity of the latter 

 part, it does not in all, and the margins of the orifice are 

 united by ligament to those of that cavity. Indeed, in 

 the Coleoptera and others that have a somewhat promi- 

 nent metaphragm a , the trunk may with more pro- 

 priety be said to inosculate in the abdomen. With re- 

 gard to the second section, — those in which the orifice is 

 of less diameter than the base, occupying only a portion 

 of it, — it may be further subdivided into those whose ab- 

 domen is sessile, and those in which it is united to the 

 trunk by the intervention of a long or short pedicle or 

 footstalk : to the first of these subdivisions belong all 

 those Diptera that have an incision between the trunk 

 and abdomen — for many tribes of this Order, as the Ti- 

 pididce, Asilidce, &c, belong rather to \hejirst section — 

 and the Araneidtf; the abdomen, however, mall is merely 

 suspended, without any inosculation. To the second 

 subdivision belong all the Hymenoptera, except the Ten- 



A Anatom. Compar. i. 450. 



