Almost a century and a half of study produced substantial progress in our understanding of
glial cells and their development. As in other areas of science major advances were associated
with the discovery of new methods. These are summarized first. Most of this account describes
development of glia in the CNS. We begin with astroglia because of their known presence and
significance in early embryonic stages. Some of Åström' s unpublished evidence is included in
this section. After consideration of oligodendroglia microglia and ependymal cells we
describe the development of Schwann cells the glia found in the PNS. In general morphological
observations of developing mammalian nervous tissues (mostly rodent) are emphasized we have
also tried to include findings relevant to cytodifferentiation interactions functions and
regulation of developing glia. Of course much has been learned about glial development by
studying other species and a variety of experimental models such as tissue culture systems
grafts and mouse mutants. Selected aspects of these subjects are also included.
