ABSTRACT
TEM observation confirms previous LM analysis in both epidermis and gland features. Epidermal cells (keratinocytes) of the thumb pad of Rana esculenta and R. perezi exhibit tall polyhedral shapes and ellipsoidal nuclei (Figs. 6.9A,B). There is a somewhat variable cytoplasm density among contiguous keratinocytes, whereas rounded mitochondria with a light, inner compartment are common features (Fig. 6.9C). Relationships among epidermis and underlying dermis are rather complex and characterized in section by wave profiles that suggest adequate trophic flows between the two tissues. When thumb pad glands occur, the basal epidermal layer appears to be continuous with flattened cells of the gland neck (or intercalary tract; Figs. 6.9 C, D). On account of the basal-apical polarization of their secretory cells, mucous glands will be described from periphery to central lumen. However, no ultrastructural pattern will be provided on R. iberica, which possesses thumb pad glands with usual features. A contractile sheath, the myoepithelium, encircles the mucous secretory units (Fig. 6.10A), with smooth muscle cells characterized by a variable content of intracytoplasmic filaments. Furthermore, there is also an obvious variability in the thickness of the myoepithelial cells, which form a discontinuous layer (Fig. 6.10B). Where gaps occur, slender cytoplasmic processes emanate from the basal portions of mucocytes, and remarkably amplify their exchange surfaces. Usually the system of interstices between secretory and contractile compartments is exiguous; it is electrontransparent (Fig. 6.10B) and in repeated observations on several specimens it appears to lack any axonal profile. The basal cytoplasm of secretory cells contains the biosynthesis machinery typical of mucocytes, consisting of RER cisternae and stacked saccules of the Golgi apparatus. The former display variable shapes, ranging from slender (Fig. 6.11A), to moderately dilated (Figs. 6.10A, 6.11B), to remarkably enlarged (Fig. 6.11C). Sacculi in the Golgi apparatus are slightly dilated, and show patterns of scanty activity (Fig. 6.11D).
