1. An examination of a large number of toads has confirmed the conclusion that unilateral integrity of the sensory and motor nerve supply to one segment is necessary for the maintenance of the normal diagonal pattern of ambulation. The site of the intact segment is immaterial; segments of the body are equally effective as those of a limb provided the number of sensory nerve fibres is approximately the same.
2. If three limbs and the body are de-afferentated, a stimulus applied to the fourth intact limb can evoke well co-ordinated ambulation in all four limbs. If the motor roots of the fourth limb are cut, a stimulus applied to this limb invariably elicits only a monophasic response in each of the remaining three limbs. The nature of the monophasic response is always such as tends to move the body away from the source of stimulation.
3. A central nervous system totally isolated from stimulation of proprioceptor or labyrinthine origin cannot sustain co-ordinated movements of a toad either on land or in water.