Front of head not touching the coxae. .......... I. Heteroptera.
Front of head much inflexed so as to be in contact with the coxae. .......... II. Homoptera.
Sub-Order I. Heteroptera.
Posterior coxae nearly globose, partly embedded in cavities, and having a rotatory movement. Mostly terrestrial forms. .......... 1. Trochalopoda.
Posterior coxae not globose, larger, and not embedded; their articulation with sternum almost hinge-like. Posterior aspect of hind femur usually more or less modified for the reception of the tibia when closed on it: mostly aquatic forms. .......... 2. Pagiopoda.
Division 1. Trochalopoda.
This division includes the majority of the families of Heteroptera—viz. the whole of the terrestrial families except Saldidae, and it also includes Nepidae, a family of water-bugs.
Division 2. Pagiopoda.
This includes the six purely aquatic families of Heteroptera, except Nepidae, which appear to have very little connection with the other aquatic bugs. The only terrestrial Insects included in the family are the Saldidae; in these the femora are not modified as they are in the aquatic forms. Hemiptera that live on the surface of water, not in the water, are classed with the terrestrial species. With these exceptions this arrangement agrees with that of Gymnocerata and Cryptocerata as usually adopted,[[482]] and therefore followed in the following pages. Schiödte's characters, moreover, do not divide his two divisions at all sharply.
Sub-Order II. Homoptera.