Correlations between the morpho-functional organization of some parts of visual analyzer and ecology in Chelonia: II. Morpho-functional characteristics of the visual nerve and tectum after unilateral enucleation.

The morpho-functional characteristics of the optic nerve and tectum opticum were studied electronmicroscopically and electrophysiologically after unilateral enucleation in 4 Chelonia species. Different types of degeneration of the myelinated and unmyelinated optic fibers and their endings in the tectum are revealed. Comparison of the types and times of the degeneration of retinal axons and their terminals with changes of the tectum evoked potentials at different times after enucleation gives ground to conclude that myelinated fibers produce nerve endings degenerating on the dark pattern and unmyelinated, all the remaining endings with the light, neurofilamentous, glycogenous, vesicular and other degeneration patterns. A stratal arrangement of the retino-tectal projections of various type fibers is demonstrated. Asynchrony of the process of degeneration of different groups of fibers and the relationship between the rate of degeneration and the diameter of myelinated fibers, as well as the absence of a relationship between the change pattern and the diameters of myelinated and unmyelinated axons are revealed. In land tortoises and water turtles differences are revealed in the set of major degeneration patterns and their endings also in the patterns of stratal distribution of various categories of the retinal fibers and tectum. A possible relationship is proposed between the above differences and ecological properties of the Chelonia groups under study. Also revealed are species-specific features of some substantial aspects of the morpho-functional organization of the levels of the visual analyzer in Chelonia.