An electron microscopic study of the cavernous bodies in the lamprey gill filaments.

The cavernous body in the lamprey gill filament was studied by electron microscopy. This body lies along the outer border of the axial plate of each gill filament and freely communicates with an afferent filament artery. Two series of blood channels run alternately, passing through the cavernous body, and lead to the marginal channels in the secondary lamellae. On the other hand, narrow blood spaces left in the cavernous body lead to the blood lacunae in the axial plate (osmoregulatory region) and to those in the secondary lamellae (respiratory region). All the blood in the cavernous body is finally collected by an efferent filament artery. The cavernous body is traversed by numerous trabeculae and collagenous columns which run diagonally in the blood spaces to connect the walls of the cavernous body. All the walls of the cavernous body, including trabeculae and collagenous columns, are completely surrounded by the cytoplasmic flanges of specialized cells called here "cavernous body cells." These cells are about 30 mu in diameter and characterized by (1) association with collagenous columns or trabeculae and also by the presence of (2) coated caveolae and vesicles, (3) vacuoles and (4) cytoplasmic granules in their cytoplasm. These cells are considered to be related to the pillar cells in origin because of their close association with collagenous columns or trabecule. The functional significance of the cavernous body and the cavernous body cells is discussed.