The Effect of Labyrinthectomy on the Co-ordination of Limb Movements in the Toad

Abstract

1. After bilateral labyrinthectomy, a toad can only walk normally if the stimulus which excites it to move is applied symmetrically on the two sides of the body. If the stimulus is asymmetrical, the animal's path curves towards the unstimulated side; if the stimulus is relatively intense the animal ‘circles’ persistently towards the unstimulated side. The ambulatory response of a normal animal to an asymmetrical stimulus is dependent on both proprioceptive and labyrinthine activity. 2. After bilateral labyrinthectomy, both hindlimbs exhibit swimming movements when the animal is freely suspended in water but co-ordination between the two limbs is lost. Evidence is put forward which suggests that the swimming rhythm of the limbs may be dependent on rhythmical excitation of the membranous labyrinth. No swimming occurs when the limbs of a labyrinthectomized toad are de-afferentated. 3. The removal of both labyrinths does not abolish the power of the limbs to right the animal when placed on its back. The mechanics of the righting movement are described.