Interappendage phasing of crayfish swimmeret movements depends upon a central nervous system network of command, oscillator, and coordinating neurons. The command neurons serve to set the general excitation level in each of the segmental oscillators. The oscillator neurons in each hemi-ganglion generate the rhythmic alternations of powerstroke and returnstroke motor neuron activity. The coordinating neurons transmit the precise timing information about the state of one oscillator to other oscillators. This information can serve to advance or to delay the motor bursts driven by the other oscillators. Which effect is observed depends upon the arrival time of the coordinating neuron discharge within the cycle period of the modulated oscillator. This type of modulation leads to the prediction that a stable interappendage phase can result from situations where there is not a fixed excitability gradient among the segmental oscillators. This prediction has been verified using a cut command neuron preparation.