ULTRASTRUCTURE OF PINEAL SENSORY APPARATUS IN SOME PIPIDAE AND DISCOGLOSSIDAE

The pineal complex of the anura is a specialized organ as demonstrated with physiological and histological methods. It shows a connection with the brain by nerve fibers and an extensive vascularization. Physiological degeneration is seen only in a part of the outer segments of the sensory cells. In the pineal organ of several phylogenetically remarkable anuran species (Pipidae: Xenopus laevis, Hymenochirus boettgeri; Discoglossidae: Bombina bombina) the flattened sacs of the outer segment form more irregular arrangements than in the lateral eye receptors and overlap the inner segment. When the invaginations become more complex, irregular outer segments are frequently observed. In such outer segments degeneration occurs in either of two ways: 1. The membrane complexes are discarded from the apex, 2. lysis starts in the basal portion. These observations are discussed considering the energyutilization aspects. - The supporting cells seem to have trophic and phagocytic functions. These cells contain also myeloid bodies with unknown function. - The plexiform region of the pineal organ contains, in addition to the basal processes of the receptor cells and the dendrites of the nerve cells, also myelinated and unmyelinated nerve fibers. The unmyelinated fibers contain dense-core granules. Besides many vesicles with a diameter of 500 Å, there are also some dense-core granules in the basal processes of the receptor cells; the functional role of these inclusions is still open to discussion. © 1968 Springer-Verlag.