Fig. 5.

Differentiation of the juvenile cuticle II. a, b The surface of late S27 embryos is not wrinkled, but rough with a few pleats. SEM. c The epicuticle differentiates with different modes at the ventral (ven) and dorsal (dor) halves of the animal (aj adherens junction). The border between the dorsal and the ventral cuticle coincides with the cell-cell boundaries (EC embryonic cuticle). d The precuticle (pre) lacks chitin. e, f Epicuticular electron-dense material is secreted between corrugations (cor) at the apical plasma membrane (black arrows in e and f) and deposited underneath the envelope (envII) at both the ventral and the dorsal side of the embryo, respectively. Microtubules (circles in cross section, white arrow) run through the plasma membrane corrugations. At the ventral side, cuticular denticle-like structures bulge out regularly (e). At the dorsal side, the envelope intrudes into the developing epicuticle to surround the electron-dense material (f). Inset f′: Higher magnification of the intruding envelope. TEM. Bars 200 μm (a), 40 μm (b), 500 nm (c–f, inset f′)