Function, homology and terminology in insect wings

Abstract. The history of current systems of wing nomenclature is summarized, and the underlying principles reviewed. The homologies of wing areas are clarified, with particular reference to the functions and positions of longitudinal lines of bending in the wings. Distinction is drawn between flexion-lines, primarily aerodynamic in function, and fold-lines, which are primarily concerned with wing-folding. Of these the claval furrow - a flexion-line - and the jugal fold-line are, when recognizable, nearly constant in position, and are hence valid area boundaries and useful landmarks in vein identification. The vannal fold-line and the median flexion-line are variable in position, and hence unsatisfactory area boundaries. The nature and functioning of fold- and flexion-lines in the axilla of Locusta are described and illustrated, and names are proposed. Conflicting aspects of commonly-used systems of wing terminology are evaluated; and illustrated recommendations are put forward for consistent naming of veins, branches and wing areas.