Cell division theories that assume that the mitotic apparatus is part of the physical division mechanism have an appealing simplicity, because both the origin of the motive force and the reason why the furrow is positioned as it is are explained at the same time. When the possibility that the mitotic apparatus plays a physically active role was disproven, a new set of problems concerning the basis of the correlation between mitosis and cytokinesis required solution. It was necessary to explain how the division mechanism normally develops in the surface at the right time and place and in the right orientation. The realization that there is an apparently separate establishment process adds further complication, and it now appears that the formation of the mechanism contains more unknowns than its function. But the complications have provided more opportunities for experimentation. Investigations have yielded information about the division mechanism as well as the events that put it in operation. The basic assumptions associated with the process are simple: (1) Before the division mechanism functions, the characteristics of the surface are uniform; (2) the effect of the mitotic apparatus upon the surface is not uniform, and it produces regionally different characteristics; (3) the surface characteristics of the region that are most affected by the mitotic apparatus are the ones changed the most; and (4) the mitotic apparatus–dependent change precipitates division.