VARIATION OF TECTAL MORPHOLOGY IN TELEOST FISHES

The morphological organization of the optic tectum was analyzed in a number of divergent teleost species. Particular attention was focused on the organization of the periventricular gray zone and of afferent and efferent fiber systems within or adjacent to it. A dorsal part of the periventricular gray zone is recognized which is in register with the distribution of tangentially and radially oriented fascicles. A lateral part of the periventricular gray can be identified as being lateral to the lateral-most of the tangentially and radially oriented fascicles and being in register with a large number of circular fascicles in the deep white zone. Circular fascicles pass between the lateral part of the periventricular gray and a more ventral part. There are few if any circular fascicles in the part of the deep white zone that is in register with the ventral part of the gray. These parts of the periventricular gray are most clearly apparent in clupeomorph fishes, due to an exaggerated separation related to the presence of two tectal lobes within the hemisphere. It is hypothesized that the dorsal part of the gray, as can be recognized cytoarchitectonically, is in register with the projection of the dorsal optic tract and that the lateral and ventral parts of the gray are in register with the projection of the ventral optic tract.