698 EXTERNAL ANATOMY OF INSECTS. 
elytra or tegmina, that part, as was requisite for its pro- 
tection, 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 Araneide, 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 inall, 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*, the trunk may with more propriety 
be said to inosculate in the abdomen. With regard 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 abdo- 
men is sessile, and those in which it is united to the trunk 
by the intervention of a long or short pedicle or foot= 
stalk: to the first of these subdivisions belong all those 
Diptera that have an incision between the trunk and ab- 
domen—for many tribes of this Order, as the Tipulidae, 
Asilide, &c., belong rather to the first section—and the 
Araneide ; the abdomen, however, in all is merely sus- 
pended, without any inosculation. ‘To the second sub- 
division belong all the Hymenoptera, except the Tenthre- 
a Anatom. Compar. 1, 450. 
