Fig. 5. Pavement cells in the gill epithelium of an upstream migrant of Lampetra fluviatilis. (A) The two-layered lamellar epithelium contains an outer layer of pavement cells (PC) and an inner layer of basal cells (BC). The pavement cells contain numerous ovoid mucous granules (arrows) and a few mitochondria. Freeze fracture of the apical membrane of the pavement cell showing few particles on the P face (B) and numerous particles on the E face (C). Scale bars, 2 µm (A) and 0.25 µm (B,C).