Fig. 3.

Differentiation of the embryonic cuticle II. a A wrinkled membrane covers the embryos at S24−S26 (here, S25). SEM. b Randomly oriented fibres that have a diameter of 100 nm are tightly packed underneath the membrane (env envelope) that has been disrupted manually (S25). SEM. c As detected with gold-conjugated WGA (black dots), this layer contains chitin (S24). TEM, cross section. d In tangential section, the apical plasma membrane during chitin synthesis carries regularly spaced microvillus-like structures (mv) that have electron-dense tips, the so-called plaques (S25). TEM, tangential section entering from the cuticle at the right side into the epidermal cell (left). Inset d’: Longitudinally sectioned microvillus-like structures (egg eggshell). TEM, longitudinal section. e In early S26, the apical plasma membrane of the epidermal cells is smooth and chitin production is terminated (EC embryonic cuticle). TEM, cross section. Bars 100 μm (a), 3 μm (b), 1 μm (c–e)