(A,B) Simplified representative sketch of y-direction flows during cell divisions observed in early development. The cleavage furrow is represented by the dotted line and is marked by high concentration of myosin (grey-shaded area). Black arrows represent y-direction flow in the two halves of the the dividing cell. (A) depicts chiral net-rotating flows, observed in the P/EMS lineage, in which both halves move in the same direction. (B) depicts chiral counter-rotating flows, observed in the AB lineage, where the two halves of the dividing cell rotate in opposite direction. Notably, both these types of flow are chiral. (C) Schematic illustrating the measured chiral counter-rotating velocities in a dividing cell. . Here, , and are orthonormal vectors depicted in left corner. In this definition, the magnitude of gives us the speed of the flows and the sign of denotes the handedness of chiral counter-rotating flows. In this sketch, the counter-rotating pair has right-handedness as observed in the AB lineage (see Materials and methods for more information on definition of handedness and ; upper left indicates the coordinate system). (D, E) Chiral counter-rotating flow speed () measured over seven subsequent frames for different stages for (D) the P0 and (E) the AB cell from the beginning of cytokinesis until completion of cytokinesis. Vertical black line marks the 10% cytokinetic furrow ingression, used as a reference timepoint to measure . The curve represents the mean , grey-shaded bar indicates error of the mean at 95% confidence interval. Inset, colored cell indicates the cell analyzed. (F) Total flow speed measured over seven subsequent frames for different stages for the AB cell from the onset of cytokinesis until late cytokinesis. Vertical black line marks the 10% cytokinetic furrow ingression, used as a reference timepoint to measure flow speed. The curve represents the mean flow speed, grey-shaded bar indicates error of the mean at 95% confidence interval.