Supplement May 1974

The investigation is a light microscopical study of the structural development of the lamprey labyrinth, especially in Lampetra fluviatilis. Some comparisons have been made with Lampetra planeri and Petromyzon marinus. The following parts of the ear have been investigated; macula communis, its subdivision and innervation; the semicircular ducts and their ampullae; the two endolymphatic ducts and the ciliated chambers. Particular attention has been paid to the origin of these parts, the function of the ciliated chambers and the ampullae. On the basis of the present knowledge of the labyrinth an attempt has been made to see how the structural changes in it during the life cycle of the river lamprey harmonize with its way of living. Also comparative and phylogenetic aspects of the lamprey labyrinth have been made.