Abstract 1. 1. Reflex retraction of the foot of the razor clam is evoked by mechanical stimulation of the foot or collar. Retraction is also a component of other reflex movements involving the foot, such as burrowing. 2. 2. Nerves from the pedal ganglia innervate the foot musculature. Tetanic electrical stimulation applied to the peripheral stump of a cut pedal nerve produces rigid contraction in a portion of the foot. 3. 3. The pedal ganglia are joined to the rest of the central nervous system by the cerebropedal connectives. Stimulation of the pedal ganglia by means of an electrode on the pedal end of a cut cerebropedal connective produces foot movements which are co-ordinated, involve the entire foot and often are sequential. The movements are usually fragments of normal reflex activity. The experiments imply that the pedal ganglia contain motor centers which generate reflex movements of the foot. 4. 4. Tetanic stimulation at various frequencies applied to the peripheral stump of a pedal nerve reveals two retracting systems in the foot: a fast system which contracts quickly, fatigues easily and reaches maximal tension at low frequencies of stimulation, and a slow system which contracts slowly, fatigues slowly and reaches maximal tension at high stimulus frequencies. 5. 5. Motor activity in intact pedal nerves and foot tension were recorded simultaneously during reflex withdrawal of the foot. The retraction elicited by mechanical stimulation of the foot consists of three phases of motor nerve activity and corresponding tension development. Tension amplitude during the reflex is proportional to motor nerve activity, except for the period of relaxation, when tension declines more slowly than nerve activity.