EXTERNAL ANATOMY OF INSECTS. 615 
terminating, after proceeding about one-fourth of its 
length, in a hollow cavity, which, as it is covered by a 
membrane, appears to me to be a collapsed pouch. This 
circumstance is worthy of further and more general in- 
vestigation. 
5. In their shape, with few exceptions, hemelytra more 
or less represent a wedge, being wider at their apex, 
where they are usually obliquely truncated, than at the 
base; but in Plea they are obtusangular, with the angle 
in the sutural margin; in Notonecta, on the contrary, an 
obtusangular sinus distinguishes that part; in Naucoris 
they are curvilinear and every where of equal width; in 
Ranatra they are linear and straight; in Aradus they 
are oblong, usually with an external lobe or dilatation 
at their base: a remarkable instance of the intention of 
this is observable in a nondescript Brazilian species, in 
which the head, prothorax, and abdomen, are edged 
with a number of broad foliaceous appendages; if the 
base of the hemelytrum had not been furnished with a 
similar appendage, the symmetry of the whole body 
would have been destroyed by the hiatus between the 
prothorax and abdomen, as may be seen by removing 
the hemelytra ; but by this compensating contrivance of 
Providence, the gap is filled, the above lobe fitting ex- 
actly into it. 
6. The neuration of these organs will not occupy us 
long, since the corium or harder part, though in some spe- 
cies there are traces of nervures, is often without them. 
Those of the cucullated species of Tings and Dictysusta 
esemble many ¢egmzna in being ornamented by them with 
a kind of network, which looks like the finest lace; in 
several Lygai, Edessa, and some Reduvii, there are a 
