Fig. 2. Analysis of pirouette initiation and execution. (A) Instantaneous pirouette rate as a function of the value of dC/dt for wild-type and mutant animals in NH₄Cl gradients. The data have been smoothed with a box filter (4001 points long). The gray line represents unc-23 data (21 293 points); the black line represents wild-type data (29 171 points). Spontaneous or basal pirouette rates measured in the absence of a gradient are represented by horizontal lines (black broken line, wild-type; gray dotted, unc-23). (B–D) Histograms of bearings immediately before pirouettes (B), immediately after pirouettes (C), and changes in bearing (D) for the animals in A. The wild-type distributions (black lines) contain 1129 pirouettes; the unc-23 distributions (solid gray bars) contain 816 pirouettes. Arrowheads indicate the angle of the vector average for each distribution; numbers indicate the corresponding vector magnitude.