Figure 3.

Swimming behavior in the nearly intact leech and its lack of dependence on descending signals. A, Number of spontaneous swim episodes (uninterrupted bouts of swimming) in a 5 min interval for each condition (preblock, blocked, postblock). Overt swim bouts were easily discerned as the animal did not pause between successive swim cycles. B, Total number of spontaneous swim cycles in a 5 min interval for each experimental condition. C, Number of spontaneous cycles per swim episode for each experimental condition. D, Number of trials (out of 5) in which swimming was elicited after gently stroking the dorsal body surface. All bars represent swimming in high water conditions (10 mm depth). No leeches swam in low water (<1 mm depth). *p < 0.05, **p < 0.01. Error bars are ±SEM. n = 8 leeches.