‖n. [ NL. See A- not, and Mitosis. ] (Biol.) Cell division in which there is first a simple cleavage of the nucleus without change in its structure (such as the formation of chromosomes), followed by the division of the cytoplasm; direct cell division; -- opposed to mitosis. It is not the usual mode of division, and is believed by many to occur chiefly in highly specialized cells which are incapable of long-continued multiplication, in transitory structures, and in those in early stages of degeneration. [ Webster 1913 Suppl. ]