The fine structure of lamprey epidermis. I. Introduction and mucous cells

Abstract

The larval and adult lamprey epidermis has been examined with the light and electron microscopes. The smallest and most numerous of the three epidermal cell types present (mucous cells, club cells, and granular cells) is the mucous cell. Outstanding cytological characteristics of the mucous cells include the presence of numerous desmosomal contacts with adjacent mucous cells, an outer, peripheral, fibrillar band which passes around the cell immediately adjacent to the plasma membrane, and a well-developed Golgi apparatus and rough-surfaced endoplasmic reticulum. Mucous cells lining the epidermal surface have a striking apical border consisting of numerous tubules or vertical channels which pass through the outer fibrillar band, thus providing a pathway from the apical cytoplasm of the surface mucous cells to the epidermal surface. The extensive development of the rough-surfaced endoplasmic reticulum and the Golgi apparatus suggest that both organelles are involved in the formation of a final secretory product (mucus). A discussion of the role of the mucous cell in the lamprey epidermis is given, and an attempt to relate the cell to basic epidermal cell types in other vertebrates has been made.