Figure 1.

Models to explain how the MA signals the cortex to determine the position of the cleavage furrow. (a) Astral relaxation. Signals from the astral centers induce relaxation of the cortex near the poles. (b) Equatorial stimulation by signals from the astral centers. Signals from the astral centers induce contraction of the equatorial cortex. (c) Equatorial stimulation by signals from the spindle midzone. Signals from the spindle midzone induce contraction of the equatorial cortex.