Fig. 5. The variability of pirouette latency within curls and its affect on the unc-23 model. (A) Pirouette probability by quadrant in real unc-23 worms. Quadrants I–IV are defined as in Fig. 4. Total number of pirouettes was 216. (B) Population behavior of simulated unc-23 worms that initiate pirouettes according to the probabilities in A. Imposing the probabilities in A on the model was sufficient to produce spiral tracks with opposite spiral-bias handedness. Simulated worms had a constant clockwise turning bias of 7 deg. s^–1. Each simulated worm was started near asterisks and allowed to move for the equivalent of 90 min. The gradient peak is indicated by intersection of dotted lines. The track of one simulated worm is highlighted in black; all other tracks are gray (N=50).