WITHIN the New Zealand species of the families Corixidae and Notonectidae (Hemiptera-Heteroptera), two distinct forms, depending on the development of the wings and the wing-musculature, have been recognized. In these species a proportion of the population is composed of flightless animals in which, apart from Diaprepocoris zealandiae, the indirect flight-musculature is reduced even though the two sets of wings are not significantly altered from the normal condition. In D. zealandiae the meta-wings are greatly reduced and the meso-wings differ in having a reduced membranous portion.