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Cover  This month's cover illustration shows an oligodendrocyte cultured from newborn rat optic nerve (from Kachar et al., 1986). These cells are the myelin-forming cells of the central nervous system that play a key role in nervous system function. Myelin is a multilamellar membrane sheath surrounding axons that allows fast saltatory conduction in nerve fibers (Peters et al., 1976; Ritchie 1984). Oligodendrocytes that form this membrane sheath each extend a variable number of processes, which form several myelin internodes around different axons. Any oligodendrocyte must, therefore, synthesize and transport large amounts of membrane and protein for integration into myelin membrane during myelination. Little is known about the factors or signals that regulate the synthesis and transport of these components. It is also not understood how the oligodendrocyte's extensive processes are formed and maintained. These processes are known to be rich in microtubules, but surprisingly, they lack most types of intermediate filaments. The processes display several motile activities, which include active translocation of organelles, cycles of extension, and retraction of membrane specializations. During early development, oligodendritic processes must be able to penetrate through the central nervous tissue in search of the target axons. The remarkable motile activities displayed by cultured oligodendrocytes are likely to reflect this property.