The Hemiptera are particularly distinguished from other kinds of
insects by the form of their mouth, which consists of a beak, more or
less long, composed of six parts: that is, of a lower lip, or sheath;
four internal threads, representing the mandibles and jaws of the
grinding insects, and which are the perforating parts of the beaks;
and, lastly, of the upper lip or labrum. Owing to this apparatus,
these insects are essentially sucking ones, and chiefly nourish
themselves with the juices of vegetables, which they draw up with
their beak. The wings of the Hemiptera are usually four in number; in
some species they are membranous and similar to each other, and in
others the upper are of rather harder consistency than the lower ones.
In general, the former are quite different from the lower wings, and
are only membranous at the tip, whereas the other part is thick,
tough, and coriaceous.
The Hemiptera are divided into two very distinct sections. The one is
composed of insects whose beak grows from the forehead or upper part
of the head, and whose anterior wings are half coriaceous and half
membranous, having the base of a different texture from the extremity:
these are the Heteroptera ([Greek: heteros], different; [Greek:
pteron], wing). The other section is composed of those whose beak
grows from the lower part of the head, and whose anterior wings are
always of the same consistency throughout: these are the Homoptera
([Greek: homos], the same; [Greek: pteron], wing). We are about to
give the history of these two sub-orders.