Comparative study on the teleostean optic tectum. Lamination and cytoarchitecture.

Seventy-five species of teleosts were studied by a modified Bodian and the Golgi-Cox method to clarify certain relationship between habits and laminar formation in the optic tectum. The optic tectum of all species studied was divided into four layers (SM, 20 + SFGS, SGC + SAC and SPV) depending upon fiber connections with other areas, and the relative thickness of each layer was measured. All animals were classified into 8 groups (thick SM, thin SM, thick SO + SFGS, thin SO + SFGS, thick SGC + SAC, thick SPV, thin SPV and standard) based on relative thickness of each layer. The thick SM group has the large torus longitudinalis. The SO + SFGS group comprises diurnal, especially visually active fishes. As relative thickness of surface layers (SM and SO + SFGS) increases, the absolute value of whole layers becomes large. Aniamls with large relative thickness of the deepest layer (SPV) show the thin optic tectum. Seven types of cells, (a) pyramidal cell, (b) fusiform cell, (c) periventricular cell, (d) pyriform cell, (e) large multipolar cell, (f) horizontal cell and (g) small multipolar cell, were classified in Golgi-Cox preparations, and the extent of dendritic arborization was compared among the groups in relation to the thickness of each layer. Dendritis of pyramidal, fusiform and preiventricular neurons show varoius extents of arborization in proportion to thickness of layers where branch out. Other types of neuron do not conspicously vary in different groups. Animals belonging to the thick SPV group show poor dendritic arborization in all types of cells. These results were discussed from the ecological standpoint.