HYMENOPTERA. 7% 
catch the hinder margin of the anterior wings, thus producing one 
continuous surface on each side. 
The legs are generally long and slender, and the tarsi (except in 
a few minute species, — Eulophus,) are 5-jointed. In the females of 
many fossorial species the anterior tibize and tarsi are furnished with 
strong lateral bristles, useful in clearing away the sand in nidification ; 
and, in the bees, the basal joint of the tarsi is greatly increased in 
size: these and other modifications of form are consequent upon di- 
versity of economy. 
The abdomen is very variable in the number of its segments, espe- 
cially in the Terebrantia. In the Aculeata it is, for the most part, com- 
posed of seven segments in the males, and six in the females. Its form 
is also very various; in some species being sessile or attached to the 
posterior part of the thorax by its entire breadth, and, in others, being 
connected therewith by a more or less slender peduncle. In the fe- 
males this part of the body is furnished with an instrument consisting 
of five or six valves, or sete. Although the various uses to which this 
instrument is applied, in the different groups, as a borer, saw, or ve- 
nomous sting, require correspondent modifications in structure, yet it 
appears to me that a typical formation is to be traced throughout 
the various forms under which it appears; it is defended exter- 
nally by a pair of lateral flattened plates, articulated near the centre, 
or, rather, near the point where they emerge from the anal cavity, 
the edges being externally applied closely together, forming a sheath 
for the protection of the internal organs, which consist of a pair of 
darts, or retroserrated spiculz, which are alternately thrust forward 
and withdrawn, being themselves enclosed in an internal sheath. In 
the aculeated tribes, the latter, enclosing the two spicule, constitutes 
the sting, but they are so fine that they appear to the naked eye to 
consist but of a single piece, the articulated sheaths being internal. In 
the Ichneumons with exserted ovipositors, the two sheaths are equally 
exserted, constituting the two sheaths of the ovipositor itself, which, 
although appearing like a simple bristle, is formed like the sting of 
the bees, &c. Inthe saw-flies, the spiculz are broad, serving as saws, 
the internal sheath being also flattened and divided along its whole 
length into two portions, forming supports, like the thickened backs of 
the ordinary hand-saw to the saws themselves. The outer sheaths are 
distinct and broad, the saws lodging between them when unemployed. 
Saint Fargeau regards the ovipositor, or oviscapte, as he terms it, and the 
