Wings four: neuration generally areolate[1200].
Prothorax obsolete, giving place to an ample collar.
Tarsi pentamerous.
Ovipositor 5-6-valved, the vagina darting forth two retroserrulate spiculæ.
** orders in which all the ordinary Trophi do not occur, or the Mouth is imperfect[1201] (Haustellata).
7. Hemiptera[1202] (Ryngota F.). Linné at first confined this Order to those insects which have a promuscis, which he denominated a rostrum[1203]; but afterwards, convinced that the Orthoptera of the moderns could not be associated properly with the Coleoptera; instead of forming them into a distinct Order, as nature would have dictated—perhaps to avoid the multiplication of Orders and without altering his definition—with equal infelicity he added them to this. Subsequent Entomologists, who saw the impropriety of masticating insects thus herding with suctorious ones, restricted the Order to its old limits; but Latreille very judiciously altered its arrangement, and divided it into two Sections, separating those whose hemelytra terminate in membrane, from those in which they are mostly tegmina, or of a substance intermediate between that of the elytra of Coleoptera and that of the wings of the Tetrapterous Orders. He denominated the first of these sections, or rather suborders, Heteroptera, and the last Homoptera[1204]. Dr. Leach, observing that very considerable differences take place both in the economy and structure of Heteropterous and Homopterous insects, followed De Geer in considering them as separate Orders, which he has called Hemiptera and Omoptera, and in which he has been followed by Mr. MacLeay; who, however, with his usual accuracy and judgment, has restored the aspirate to the latter name[1205]. Their agreement in having a promuscis, or instrument of suction, with a jointed sheath, at present induces me to hesitate as to the propriety of their separation, and to consider them as forming secondary rather than primary sections of the Class. That you may be enabled to judge for yourself upon this subject, I will state the principal features in which they differ. In the first place, the Heteropterous section usually sucks the juices of animals, and the Homopterous, those of plants; in the former, the Hemelytra, besides their different substance, as well as the wings, cross each other; while in the latter, the organs of flight are deflexed, and do not lap over each other at all. The antennæ also of the one are often long, and do not terminate in a bristle; while in the other, with few exceptions, they are very short and setigerous. In the Heteroptera the body is depressed and flat, in the Homoptera convex and thick. In the former, the scutellum is one of the principal features of the trunk; in the latter, not at all remarkable[1206]. Other differences in the structure, both of head, trunk, and abdomen, might be pointed out; but these you will chiefly find noticed in my letters on the External Anatomy of Insects, where I treated of those parts. I shall here, therefore, only further mention the ovipositor also as forming a most striking distinction[1207].
Def. Metamorphosis semicomplete in almost all.
Mouth promuscidate[1208].