Fig. 6. TEM sections of wing epidermis of wildtype (A,C) and Df(1)MR (B,D) at 36 hours APF (A,B) and 44 hours APF (C,D) (bar, 500 nm). The insets correspond to micrographs of thick sections of the same specimens, stained with toloudine blue and showing the whole wing (bar, 50 µm). (A) At 36 hours APF, the small patches of cuticulin envelope (arrowheads) appear at the tip of microvilli (mv) in the wildtype. (B) In the mutant, microvilli are shorter, and the process of cuticle deposition is less advanced (arrowheads). (C) At 44 hours APF, the cuticulin envelope forms an almost continuous layer over the epidermis in both wild-type and mutant wings. In some regions (arrowheads), the characteristic trilayer can be observed, whereas in other regions (brackets) the cuticulin layer seems less organised. (D) The structure of the apical microvilli is disorganised in the mutant wings (mv). The process of wing extension is prevented in the Df(1)MR mutant (compare insets in C and D).