A honeycomb-like tubular array was observed in heavily myelinated axons. It was observed in the cerebellum of an apparently normal rat and a chimpanzee with “Kurulike” symptoms. It was also found in the cerebral cortex of a mouse that had had a intracerebral tumor implant. A common underlying etiology could not be found. It is suggested, however, that this structure represents a specific axonal response to perhaps a variety of as yet unknown conditions.