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Åström' s unpublished evidence is included in this section.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.