Mitotic division of oligodendrocytes which have begun myelination

Examination of spinal cords of 5 days old mice showed a number of examples of oligodendrocytes, in various phases of mitosis, which remained in contact with the axons which they were myelinating. Cells in prophases had thick processes between the perikaryon and the myelinating axons but as mitosis proceeded the oligodendrocyte processes became thin and spider-like, probably due to the extrusion of cytoplasm from the processes into the perikaryon. Mitotic astrocytes were also present.