Inductive mechanisms in the process of wing vein formation inDrosophila.

The mechanisms underlying the formation of veins in the wing ofDrosophila have been studied by means of clonal analysis. To this end the phenotype of vein-suppression mutants (crossveinless, veinlet andradius incompletus), the vein-addition mutantplexus and a mutant causing the appearance of chaetae on the wing veins (hairy) were analysed both singly and in double mutant combinations. Subsequently various combinations of these mutants were studied in genetic mosaics. The results indicate that the cells of the dorsal surface of the wing express their genetic constitution autonomously with respect to these mutations. The ventral surface, however, has a non-autonomous behaviour with respect to vein formation but an autonomous one with respect to chaeta differentiation. Since chaeta differentiation is determined before puparium formation, i.e. before both wing surfaces some into contact, it is suggested that vein determination results from a genetic decision occurring autonomously and independently in the cells of both wing surfaces, also prior to pupariation. The final extension and course of the wing veins are modulated by cells of the dorsal surface inducing the genetically competent cells of the ventral surface.