SummaryThe cerebellum of DPH intoxicated rats were studied. Various types of unusual structures including vacuoles, tubules and honeycomb structures were observed in the axons of the granular cell layer. Though the observations of these structures, it was concluded that there are two types of honeycomb structures and that a developmental sequence of stage from vacuoles to honeycomb structures exists, which can be summarized as follows:Stage 1: Vacuoles with fine granules on their membranes appear showing some relations with the mitochondria.Stage 2: From the vacuoles one or more tubules with fine granules spirally arrayed thereon sprout and gradually lengthen.Stage 3: The lengthened tubules are assembled and arrayed in parallel and the cut‐ends of tubules show honeycomb structures.Stage 4: Each of the lengthened tubules swells torturously, as a result another type of honeycomb structure is see