1. High-speed motion pictures of the metachronous movements of the abdominal swimmerets of the lobster Homarus americanus were analysed. Measurements were made on films produced before and after removing part or all of individual swimmerets.

2. Analysis of the intact swimmeret system provided quantitative constraints for models of the neural mechanisms underlying swimmeret beating. For example, the conduction velocity of the anterior-moving, metachronous wave increases with increasing frequency of swimmeret beating, as does the powerstroke amplitude and velocity of each swimmeret. The phase positions of individual swimmerets in the movement cycle are the same regardless of the frequency of swimmeret beating, and so are the ratios of powerstoke duration to returnstroke duration. The durations of the powerstroke, returnstroke and the short pauses between them decrease as the frequency of swimmeret beating increases.

3. Removal of a swimmeret weakens the movements of ipsilateral swimmerets on adjacent segments, but does not affect the movements of contralateral swimmerets. Control experiments were performed to reduce the possibility that the effects were mechanical.

4. The results suggest that proprioceptive feedback from the movements of individual swimmerets plays a supplemental role in the intersegmental coordination of the swimmerets of one side, but that contralateral proprioceptive influences are weak or absent.

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