[Architecture of the visual system of Discoglossus pictus (Oth)]

Abstract

The retinofugal pathways of an "archaic" Anura Discogossus pictus were examinated with Fink-Heimer method following ablation of the retina and after survival times of 5--105 days at 14 degrees C. A description of the diencephalic and mensencephalic architectonics has been done in order to replace the visual system into the general pattern. The scheme of primary optic pathways and centers is similar in Discoglossus and Rana. However, some retinofugal fibers reach the posterolateral part of the ipsilateral tectum opticum. Beside this study, a Golgi study has shown the link which exists between the degeneration territories (neuropils) and the periventricular cell-masses by the way of the dendritic trees of multipolar, bipolar and pear-shaped neurons. An hypothesis about the notion of visual center is formulated. In the tectum, the distribution of degenerations allows to understand the existence of two visual behaviors: avoidance and prey-catching. The signification of the ipsilateral retinotectal pathway is discussed.