Fig. 5.

Light microscopy (A, B, and E) and TEM images (C and D) of the aboral epithelium. (A) A thin layer (∼10 μm) of brown pigments is visible on the surface of the aboral epithelium cells. Scale bar = 20 μm. (B) Only the glandular cells (here cell type 2), but not the pigment layer itself, react to any histochemical test (e.g., alcian blue at pH 2.5). Scale bar = 50 μm. (C) A second pigment layer (∼5 μm) is visible near the basal membrane of the oral and aboral ridges and contains electron-dense granules (gr). Scale bar = 2 μm. (D) Interstitial cells (in) with densely arranged microvilli and a centrally orientated nucleus (nu) are visible between the glandular cells of the oral and aboral epithelia. Scale bar = 2 μm. (E) The basal lamina of the aboral epithelium revealed strong reactivity to UEA (staining for fucose). Scale bar = 20 μm.