Biol. the indirect and more common method of nuclear division of cells, consisting typically of prophase, metaphase, anaphase, and telophase: the nuclear chromatin first appears as long threads which shorten and thicken to form the typical number of chromosomes, each of which splits lengthwise to double in number with half of each set then moving toward opposite poles of the cell to become reorganized into two new nuclei with the normal number of chromosomes