Df(1)m-MR is hemizygous viable. Resulting adults have wings that are smaller than normal although the wing veins are correctly patterned. Wing hairs are much closer together than normal, suggesting that cell size is reduced. Mutant hairs are twisted and branched. Cuticular blobs bulge out of the main wing surface. The dorsal and ventral wing surfaces are separate in the mutants, instead of closely apposed as in wild type, with the space between them filled with cell debris and cuticle invaginations. Cuticle covering the epidermis of other parts of the body appears completely normal. Morphology of Df(1)m-MR mutant cells at 28-32 hours APF show no abnormalities. Between 42 and 48 hours APF mutant cells do not undergo the flattening characteristic of wild type cells, and the prominent actin-filled extensions - the hair pedestals - do not form. Actin accumulation is abnormal - the actin forms a ring in the apical part of the mutant cells. By 62-66 hours APF, when wild type apical cell membrane is secreting the chitinous cuticle, the Df(1)m-MR apical membrane folds deeply into the cleft between adjacent cells. Formation of the cuticulin envelope is not prevented in Df(1)m-MR wings, though the microvilli underlying the cuticulin layer are shorter and membrane invaginations beneath the cuticulin layer are more extensive and less well organised than in wild type.