EYE STABILIZATION BY STATOCYST MEDIATED OCULOMOTOR REFLEX IN NAUTILUS

Nautilus pompilius can rotate its eye relative to its body so as to compensate for changes in its body orientation and maintain its eye fixed with respect to gravity. An ocular compensation reflex stabilizes its eye about the pitch axis against the rocking motions that occur as the animal swims by jet propulsion. The eye is not held absolutely still, as 1-2° spontaneous rotations occur even if the animal is clamped. If the animal is held in an unnatural orientation (rotated about the axis through its laterally directed eyes) the counterrotation of the eye is maintained for many minutes; it may compensate for 50-90% of imposed tilts up to ±30°. If the nautilus is tilted suddenly forward or backward, its compensation reflex is 50% complete within 0.3 s, and is complete in 1-2 s. The time course of the responses explains how the eye, during the 1 Hz rocking caused by swimming, can be held fixed in space to within 1-4°. The ocular compensation of each eye is mediated largely by the homolateral statocyst, as is shown by unilateral and bilateral ablation. The effect of ocular compensation is to keep image orientation on the retina fixed relative to gravity, and to prevent large rotational image motions from being caused by the nautilus's own swimming. © 1979 Springer-Verlag.