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The ependyma of the hypothalamic third ventricle of Natrix maura (L) has been investigated by light microscopy employing Nissl and Golgi stains. Electron microscopy was also used. Brains were fixed by intraventricular perfusion and embedded in paraffin, celloidin and Spurr resin. Light-microscopically the ependyma appears as a simple layer epithelium with round or enlarged nuclei. It sometimes shows basal processes extending into the subependymal tissue. These processes can be clearly seen in Richardson stained semithin sections. They often contact the subependymal capillaries. Electronmicroscopically, tanycytes contacting capillaries show numerous microvilli and few cilia as well as pinocytotic vesicles at their apical surfaces. There are zonulae adherentes and probably gap junctions as well as digitations and desmosomes. In the apical cytoplasm there are mainly mitochondria, endoplasmic reticulum and Golgi apparatus. Near the nuclei and specially in the basal process there are many microtubules. The tanycytes contact the capillaries by an end foot containing mitochondria and pinocytotic vesicles, which are also observed in the endothelian cytoplasm. These structures lead us to think, like several other authors, that the tanycytes of Natrix maura (L) may serve as a linkage between CSF and the capillaries and that they possess the morphological features which are necessary to effect intracellular transportation.

The separate cellular regions of the reptilian cerebral cortex were studied using Numerical Taxonomy. Three parameters were employed: a) The area occupied by each region at the several levels studied. b) The total area of the cell nuclei present in each level. c) The average are of these nuclei. Numerical Taxonomy resolves the problem by means of a dendrogram which represents the normalised distances, which indicate levels of similarity on absciassas. The elements studies are on the ordinate axis. The dendrogram shows the different levels of similarity existing between each one of the chosen populations. Depending upon the degree of similarity one may deduce the similarities or differences existing between these populations, and also the characteristics of each cellular population throughout the length of its presence in the cerebral cortex and the variations between the regions. These results, in the first place, relate to the four cortical regions: medialis cortex, dorsomedialis cortex, dorsalis cortex, and lateralis cortex, and in the second place, to each one of the regions within the entire telencephalic cortex.

Paraphyseal epithelial cells of Natrix maura have been studied with light and electron microscopy. They showed a clear polarity apically related to the third ventricle and, basally, to a connective tissue layer which surrounded the whole organ. The apical surface of the cells, attached by junctional complexes, showed many microvilli, scarce cilia, and some pinocytotic coated vesicles. In their apical cytoplasm many mitochondria and a well-developed golgi apparatus and endoplasmic reticulum were observed. Whereas lamellar bodies were abundant and closely related with mitochondria, glycogen particles were absent. Basal cell membrane showed infoldings where pinocytotic coated vesicles were detected. In the connective tissue layer, fenestrated sinusoids and fibrocytes, as well as rare unmyelinated nerve fibers engulfed by Schwann cells, were present. The possible active role of paraphyseal cells in exchanging substances between cerebrospinal fluid and blood is discussed.

The cytoarchitecture of the intra-ocular optic nerve was investigated by light and electron microscopy. Glial cells in the intra-ocular portion are disposed among the axons, either scattered or forming columns, and bordering the nervous parenchyma. Astroglia forms the limiting glia that separates the optic nerve from the vitreous body, retina, choroid and sclera. Indentations of choroid-scleral tissue are observed in the limiting glial sheet as well as an abundance of hemidesmosomes in the astrocytic plasma membranes that abut onto the basal lamina. At the scleral level there is no connective tissue structure similar to the mammalian lamina cribrosa. However, astrocytes in this region are regularly arranged in thick columns and their processes cross throughout the nerve perpendicular to the axons, forming a framework through which the nerve fibres pass. Numerous myelinated and unmyelinated axons are present in the intra-ocular portion. Oligodendrocytes are also present in close relation with myelinated axons. A deep connective tissue septum arises from the ventral region of the optic nerve and extends along the intra-ocular portion.