Electron microscopic development of neuroglia in epiretinal portion of post-natal rabbits.

The development of epiretinal and optic nerve neuroglial cells has been studied ultrastructurally in 1-20-day post-natal rabbits. Two morphologically distinct neuroglial cells were observed, a dense "spider" type which is present from day one and a light-staining "crab" type of cell which appears on the 4th day in the epiretinal strip. "Crab" cells myelinate many axons and mature into typical dense oligodendrocytes. "Spider" cells have ultrastructural features of both astrocyte and oligodendrocyte and each cell also myelinates many axons. Many of these cells attach their processes to basement membrane of blood vessels and mature into a typical astrocyte. In 10-15-day-old animals these cells may be located at a distance of 15 micrometer or more from the axon which they enwrap. Most of these processes are sufficiently fine and tortuous to obscure the continuity in single thin sections from adult animals.