Previous classifications dealing with the cytogenesis of neuroglia have formed a working basis for the study of the neoplasms of the glioma group. With the ever increasing interest in the field of neuro-pathology, largely owing to the advent of metallic staining methods, it will be necessary to modify these classifications from time to time in order to clarify the relationship between the embryonic and the pathologic cell types. In the evolution of primitive spongioblasts to adult autonomous neuroglia can be distinguished cell types comparable to those constituting the various neoplasms arising from these cells. A review of the literature on the phylogenetic development of neuroglia, in association with an ontogenetic study of their evolution in mammals, has suggested a possible simplification of the existing classifications. The term neuroglia, as now used, applies first to the so-called classic neuroglia; this term includes the fibrous and protoplasmic astrocytes which differ only in