Abstract 1. 1. Both chordotonal receptor organs, MC1 and MC2, in the merocarpopodite joint in walking legs of the crab are stretched by flexion of this joint, whereas CP1 and CP2 are stretched by opposite movements of the carpopropodite joint, namely production and reduction, respectively. 2. 2. Afferent impulses have been recorded extracellularly from the whole sensory nerve and isolated fibres from each receptor, in response to (a) passive movement of the joint containing the organ, and (b) stretching and releasing the partially or completely excised receptor. 3. 3. Unidirectional movement and position fibres for relaxation (release) of the receptor—or the corresponding joint movement—were recorded in good numbers in all four sensory nerves. 4. 4. The nerves from MC1 also contained many movement and position fibres for receptor stretch—or joint flexion; while stretch sensitive movement and probably also position fibres are present in CP1 nerves, but are less common than relaxation fibres. In the six MC2 and six CP2 nerves studied, however, stretch sensitive fibres were not found. 5. 5. Correlations between the gross morphology and attachments of these receptors, the fine structure of their scolopidia, and their afferent responses are noted. The differentiation between ciliary adn paraciliary distal processes is not adequate to explain differential direction sensitivity. The reflex function of MC1 and MC2 and the myochordotonal organ in the base of the meropodite are considered.