On the Visual System of Nautilus Pompilius

Abstract

ABSTRACT The anatomy of the eye of Nautilus pompilius Linnaeus was studied, using light and electron microscopy. The outer and inner surfaces of the iris were found to be lined with columnar epithelium bearing microvilli, except for the groove running ventrally from the pupil over the outer surface of the iris, where the epithelial cells bear cilia. Many mucus cells are also present. The epithelium of the inner surface of the iris merges smoothly with the retina. There is no significant variation in receptor packing or rhabdome length between different parts of the retina. Screening pigment is present, but shows no photomechanical movements in response to light. Immediately beneath the retina the nerves are collected into well-organized bundles, which run in a direction suggesting that they may form an optic chiasma analogous to that found in other cephalopods. Visual acuity was also determined, using the optomotor response. The minimum separable angle was found to lie between 11·25 and 5·5°. This agrees well with the value expected on the basis of the gross dimensions of the eye and pupil, and also with expectation based on photographing a visual test chart with a scale model of the eye. It is, however, considerably worse than would be expected from the dimensions of the receptor mosaic.