[Changes in the retinotectal system of the tortoise Testudo graeca following enucleation]

Electrophysiological and electron microscopic studies have been made on degeneration in the optic nerve and midbrain tectum after enucleation of the tortoise T. graeca. It was found that intensive degeneration of terminals which follows "dark" type (1/2--1 month after enucleation) corresponds to degeneration of myelinated fibers. Mass degeneration of the "light" type is associated with degeneration of unmyelinated fibers, being observed 1 1/2--2 months after the enucleation. The main bulk of fibers and terminals degenerates at the period of 4--4 1/2 months. Changes in functional characteristics of the evoked potentials (EP) follow morphological ones and consist in an increase of the interval between the stimulus and the peak of EP components, as well as of the decrease of the amplitude of the EP. Within 4--4 1/2 months, both EP components disappear almost simultaneously.