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Ependymal cell differentiation was examined in the lizard Gallotia galloti from E31 to adult. From E31 to E34 only one type of cell could be identified making up the pseudostratified columnar neuroepithelium but by E35 to E37 three types of ependymal cell were present. The first type was a narrow, elongated, columnar cell containing rough endoplasmic reticulum filled with an amorphous ground substance similar to that of astrocytes. The second type was broader with the nucleus close to the ventricular surface with numerous lipid droplets of varying sizes in the cytoplasm. The third type had an irregularly shaped apical nucleus and a broad basal process probably extending to the pial surface. The process contained numerous microtubules, glycogen granules and a few filaments. From E38 to hatching the ependyma showed marked regional variation. Much of it was formed by a single layer of moderately dark cuboidal cells but parts were made up of a low columnar epithelium in which the cells had elongated nuclei, frequently indented on the ventricular side. Cilia were common and often cells had cytoplasmic protrusions into the ventricle. Lipid was present in the form of small apical droplets or a large basal droplet. Ependymal cells in the region of the sulcus limitans were packed with lipid as were cells of the adjacent subventricular layer. In the adult the ependymal lining varied from cuboidal to low columnar with nuclear chromatin usually arranged in a reticulated pattern. Two types of ependymal process extending to the pia could be identified. One type was packed with microfilaments whilst the other contained a core of microtubules and scattered glycogen granules. Lipid was still present in the cells of the sulcus limitans.

Oligodendrocyte development was investigated in the midbrain of the lizard Gallotia galloti using the electron microscope. Oligodendroblasts, which had a pale cytoplasm containing numerous microtubules in the perikaryon and processes, were present from E35. Active oligodendrocytes had a pale nucleus, usually containing a nucleolus, and an electron-dense cytoplasm with long parallel stacks of rough endoplasmic reticulum. These were present from E37 to hatching which coincides with the period of rapid myelination. The three types of oligodendrocyte (light, medium and dark) first classified by Mori & Leblond (1970) in the rat could be identified in the lizard. Light oligodendrocytes were present at all ages from E37 to adult. Medium oligodendrocytes first appeared at E40 and dark oligodendrocytes were present at all ages from hatching onwards.

Astrocyte development was investigated electron microscopically in the midbrain of the lizard Gallotia galloti from E32 to adult. At E32 only very immature (early) glioblasts were present in the midbrain and similar cells could be found until hatching. From E34 two other types of glioblast could be identified--dark glioblasts which had a slightly greater amount of cytoplasm than early glioblasts and light glioblasts, in which cytoplasmic organelles were more abundant. Both dark and light glioblasts were present in very small numbers in the adults. Astroblasts, which could be identified by the characteristic appearance of their rough endoplasmic reticulum, first appeared at E35, at which stage a few very immature astrocytes containing small quantities of gliofilaments were also present. With increasing age the quantity of gliofilaments in astrocyte cytoplasm increased. Astrocytes in the adult white matter contained very large amounts of gliofilaments whereas those in grey matter contained many fewer gliofilaments and had glycogen granules in their cytoplasm which were rarely present in mature fibrous astrocytes.