Fig. 1.

Developmental increase in spontaneous swimming behavior. A: examples of postembryonic stage 37/38 and larval stages 45 and 47 Xenopus laevis tadpoles. Drawings kindly provided by Laurence D. Picton, with permission. B: bar graph of the displacement during swimming measured over a 5-min period at different larval stages. C: bar graph of percentage of total time spent swimming measured over 5 min at different larval stages. Insets show typical swim trajectories at stages 37/38 [2 days postfertilization (dpf)] and 45 (4 dpf). Values are means ± SE. ns, Nonsignificant. ***P < 0.001.