The indirect division of cells in which, prior to
   division of the cell protoplasm, complicated changes take place in the
   nucleus, attended with movement of the nuclear fibrils; -- opposed to
   karyostenosis. The nucleus becomes enlarged and convoluted, and finally
   the threads are separated into two groups which ultimately become
   disconnected and constitute the daughter nuclei. Called also mitosis.
   See Cell development, under Cell.