A STUDY OF EQUILIBRIUM IN THE SMOOTH DOGFISH—GALEUS CANIS (MITCHILL)

1. Bilateral Destruction of the Labyrinths Causes Disturbances of Equilibrium in All Animals.—In some animals the disturbance is more marked than in others. When the disturbance is not very marked, the animal either rotates around its longitudinal axis when swimming to the surface of the water or swims on its back and rights itself with difficulty when placed ventral side up; when the disturbance is very pronounced the animal rotates around the longitudinal, transverse and dorso-ventral axes, nose dives, spirals, and swims on its back.

2. Allowing the factor of time to intervene, the animals which suffer profound disturbances of equilibrium—such as rotation around the axes, spirals and nose diving—regain most of their equilibrium within twenty-four hours. The animal swims normally in all planes, but if placed ventral side up, it swims on its back and rights itself with difficulty.

3. After sectioning the olfactory tracts or the optic nerves, the animal's equilibrium remains normal. Movement to the right or left around the dorso-ventral axis during the first hours following the sectioning of the optic nerves can not be accepted as disturbance of equilibrium because changing the direction of the animal changes the direction of its swimming.

4. Destruction of the labyrinths after sectioning of the olfactory tracts and optic nerves disturbs the animal's equilibrium similarly as the destruction of the labyrinths alone.