The tumor cells form an unoriented mass rather than a layered structure. Most of the cells have no ependymal specialization, such as cilia, microtubular, etc. Instead, they assume a primitive undifferentiated appearance with large nuclei and abundant free ribosomes. Occasionally, however, certain cells tend to form a ring around a narrow lumen-like space within the mass. Such spaces are virtually filled with microvilli and, occasionally, even cilia arising form the surrounding cells. Elaborate desmosomes decorate the apposing surfaces of such cells and basal bodies are presented within the cytoplasm. In addition, the tumor cells often display glial filaments, glycogen granules and microtubules, similar to the cells comprising astrocytomas. As is well known, astrocytomas and ependymomas are often found mixed in the same tumor.