Fig. 4. Transmission electron micrographs of principal secretory cells from the salt gland of (A) FW-acclimated and (B) SW-acclimated C. porosus. Transverse sections through a whole cell showing ultrastructural arrangement of organelles typical of the principal secretory cells. Scale bars, 5 µm. (C) Transmission electron micrographs of principal secretory cells from the salt gland of a FW-acclimated C. porosus showing close apposition between secretory cells and capillaries. Scale bar, 5 µm. (D) High-resolution transverse section through the apical region of a principle secretory cell showing junctional complex and short, irregularly shaped microvilli protruding into the secretory tubule lumen. Scale bar, 1 µm. (E) High-resolution transverse section though the lateral margins of two adjoining cells demonstrating the interlocking arrangement of the long microvilli (plici) of the basolateral membrane. Scale bar, 1 µm. l, secretory tubule lumen; p, plicae; bm, basement membrane; n, nucleus; m, mitochondria; j, junctional complex; mv, apical microvilli; v, small, clear, apical vesicles; rbc, red blood cell; bm, basement membrane; cap, capillary; sc, secretory cell.