Cell cortex is not fully circular. (a) Representative brightfield images (first row) of HeLa cell lines expressing mCherry-Tubulin or Sir-Tubulin. Cells were selected based on measurements of eccentricity. Intact spindles of the individual cells are represented in the second row. Circular shape with eccentricity = 0 is highlighted in yellow. (b) Violin plot shows distribution (dots) of eccentricity across 96 3D live-cell movies from 16 experiments. White marker within the box refers to the median, the shaded area refers to the estimated kernel probability density and the box indicates the interquartile range of the data. Measurements from the same dataset share the same color. Scale bar: 5 µm.