Spindle angles were determined using FIJI by finding the distance between the mitotic spindle poles: (i) in the xy axis of the flattened ventrolateral ectoderm in a sum projection of the confocal z stack; (ii) in z axis by determining the z planes that the 2 poles appear. The mitotic spindle orientation angle, φ, was calculated by taking the inverse tan of the difference in z depth divided by the distance in xy between the spindle poles (Fig EV3C and D).