The fine structure of the eye of the mollusc Pecten maximus

Abstract

The retina of Pecten maximus is divided into two light sensitive layers forming the distal and proximal retinae. The cells from these layers have different electrophysiological responses, the distal cells giving primary “off” responses, and the proximal cells giving “on” responses. The receptor surfaces of the distal retinal cells are formed from lamellae produced by the outer membranes of flattened cilia. These cilia have a basal body, basal foot, no root system and a 9 + 0 internal filament content. Each cell gives rise to an axon from its distal side, and this process goes up to the basement membrane, which is present below the cellular lens, passes along beneath it, and joins the distal optic nerve. The receptor part of the proximal retinal cells is formed from a vast array of microvilli. Each of these cells also bears one or two cilia with a probable 9 + 0 internal filament complement and no roots. The proximal cells give rise to axons, forming the proximal optic nerve. Below the proximal retina is a reflecting layer, the argentea, and below this is a pigment cell layer.