By the stimulation of the ipsilateral afferent nerves of the hind limb of a decrebrated cat, the reflex effects evoked on the extensor (vastocrureus) and the flexor (semitendinosus) muscles were studied. The results may be summarized as follows.:- 1) By the stimulation of the afferent nerve-twig mixed with cutaneous and muscular nerve-fibres, the extensor relaxes and the flexor contracts when the strength of stimulation is weak, but on the contrary, this effect is reversed when the strength of stimulation is increased. 2) By the stimulation of the afferent nerve-twig which innervates muscle-fibres, the extensor relaxes and the flexor contracts at any strength of stimulation. 3) By the stimulation of the affereut nerve-twig which innervates skin, the extensor contracts and the flexor relaxes at any strength of stimulation.