A division (also known as Hemimetabola) of the subclass Pterygota, including those insects that show relatively slight change in body form with growth. They develop through a series of immature forms (nymphs) from hatchling to adult, so that wings grow as external pads and enlarge with each molt. The nymphs are often scaled-down copies of the adults, but in some cases, particularly in those orders with aquatic nymphs and aerial-terrestrial adults (such as in Ephemeroptera and Odonata), a considerable difference in body form exists between adults and their immature forms. This development, called incomplete metamorphosis, is characteristic of all Paleoptera and some members of the infraclass Neoptera (all ancestrally winged insects except Endopterygota). Most exopterygotan taxa have freely mobile nymphs with well-developed legs, although conspicuous exceptions occur in the form of the scale insects (Coccoidea) and some of their highly sedentary sap-feeding allies.