Recordings of electrical activity from the maxilliped abductor muscles of the crab Cancer during natural beating movements. (A) The rhythmic beating of the left (L3) and right (R3) maxillipeds alternates. Each compound junctional potential in the muscle corresponds to one beat of a flagellum. (B) Sequence of action of the three maxillipeds on one side, which starts with a contraction of the muscle of maxilliped 3 (R3) and is followed by maxilliped 2 (R2) and then by maxilliped 1 (R1). (C) A recording from the abductor muscle in which an increasing number of spikes in the motor neurons preceded the progressively larger compound muscle potentials.