Fig. 4. (A–H) Vorticity plots at three spanwise locations at various times during one stroke. r₁, r₂ and r₃ denote locations 0.75, 0.5 and 0.25 wing lengths from the wing root, respectively. , non-dimensional time; , angle of attack. Solid and broken vorticity lines indicate positive and negative vorticity, respectively. The magnitude of the non-dimensional vorticity at an outer contour is 1. Starting from the outer contour, for the first 21 contours, the contour interval is 0.2, for the next 30 contours, the contour interval is 0.5, and for the remainder of the contours, the contour interval is 5.