Regions defined for analysis. A. A dividing cell is imaged with excitation at 490 nm, showing GFP-myosin-II distribution. B. The same cell is imaged with excitation at 405 nm, showing the volume marker, NLS-GFP (nuclear localization signal fused to GFP) distribution. C. Division of the image in A with the image in B leads to this resulting ratio image. D. The cortex is defined as the 0.35-μm thick shell of the cell, bordered by the solid continuous lines. The cytoplasm (outlined by dashed lines) is the total volume of the cell minus the volume of the cortex. It should be noted that the fluorescence intensity of the cytoplasm in the central region of the cell included the overlying and underlying cortex. However, the contribution of these cortical components to the total fluorescence intensity of the cytoplasmic region was calculated to be less than 2%. The nuclei are encircled to mark their positions, but their combined volume is inconsequential. E. The furrow cortex region is indicated with arrowheads and the polar cortex is indicated with arrows. Bar, 5 μm.