Frames from Video 3 showing that hypotheses H1–H3 work robustly across a wide range of cell sizes to explain furrow positioning. In this case, a small (8-μm-diameter) cell that 10 division rounds would produce from the 80-μm zygote simulated in Figs. 1 and 2 is shown. As in Fig. 1, MKLP1s stall at MT tips, move at 0.2 μm/s, and bind MTs with a 20-s half-life. The resulting 4-μm mean run length is the entire radius of this cell. In Fig. 1, an MKLP1 falls off, then rebinds an MT 10 times to move from centrosome to cortex. As explained in the text, the small cell has higher tubulin and MKLP1 concentrations. To visualize all MKLP1s stalled and clustered at MT tips, we took artistic license to draw them as if spread out along the same terminal 1 μm of the MT we used in Fig. 1. The 1-μm artwork spread is a compromise, too long in comparison to the 4-μm radius of cells here but barely long enough to show up in Fig. 1. Radial density plots show MKLP1 concentrations qualitatively, as in Fig. 1, but with different scaling because this small cell has a much higher MKLP1 concentration. Note that, at t = 340 s, the signal/noise ratio of the MKLP1 concentration peak at the equator to the levels outside the furrow zone is smaller than for the 80-μm-diameter cell in Fig. 1, but we judge that this furrow specification mechanism still works in small cells. The main text explains the meaning of the red, white, and gray lines shown in the figure.