Figure 1. The subcoxal theory of the origin of the pleural sclerites.

The classic subcoxal theory states that the pleurites on the lateral insect thorax develop from an embryonic subcoxal segment. (a) Schematic showing the pleurites (red) in the mesothorax of a proturan, Eosentomon germanicum. (b) Diagram of the basic structure of a pterygote insect pleuron on a wingless thoracic segment. For clarity, the limb more distal to the subcoxa is not shown in (a,b). (c) Schematic showing segmental identities in a generalized embryonic limb. The subcoxa (which forms the pleural sclerites) is highlighted in red. (d) Schematic of the subcoxa (red) in an embryonic limb of Naucoris sp. (Rhynchota, Hemiptera). (a–c) were adapted from¹ (d) was adapted from⁶.