ABSTRACT
An operative technique is described, which makes possible the elimination of a single horizontal semicircular canal in the pike (Esox lucius).
Such an operation, carried out unilaterally, leads to a lasting tonic asymmetry of the eye muscle apparatus. Hence a tonic function of the horizontal semicircular canals must be assumed.
The eye reactions of the pike during and after rotation in a horizontal plane are in complete agreement with the properties of the ampullary sense organ of the dogfish described by Löwenstein & Sand (1936).
It is demonstrated that a single horizontal semicircular canal can give rise to reflex responses of the eyes on both clockwise and anti-clockwise rotation of the fish in the horizontal plane.
Experiments of a similar nature on normal and on blinded tench (Tinea vulgaris) have led to similar results. They are not further described here, since (owing to the anatomical peculiarities of the tench) both the operation and the subsequent observation of reflex response cannot be carried out as satisfactorily as in the pike.
This does not hold to the same extent in all fish. For instance a normal dogfish, during forward locomotion, shows a certain amount of head pendulation from side to side. Normal pike, however, keep their head perfectly steady.
