That tumors form at one or more levels of the spinal cords of patients suffering with syringomyelia is well known, though histologic studies of them have not often been published. They were considered to be gliomas, although many writers observed that, unlike ordinary gliomas, (a) such tumors do not infiltrate extensively so as to surround and include nerve cells and fibers, preexisting vessels and connective tissue elements; (b) they are part of a definite and peculiar proliferative process, of which they are but a local intensification, and (c) in these tumors associated with syringomyelia the ependyma and the undifferentiated cells lying near the central canal, which are closely related to ependymal cells, share in the proliferative process in a special, possibly a specific, way. Therefore, it will not be surprising if one finds that these tumors are composed of cells of the ependymal, rather than of the neuroglial, derivatives of