Abstract

The frequently occurring photoreceptor patterns in fish are explained using functional and environmental demands in a geometric model. The shape of the double cone provides a number of constructional properties leading to a limited number of appropriate configurations. The probability of their occurrence is estimated from the degree to which the combination of properties of each configuration meets specific environmental light conditions. A row pattern of merely double cones is especially suitable for vision in a dim homochromatic environment; a triangular pattern is quite appropriate for high resolution and accurate movement detection, whereas the known square pattern has a high adaptive capacity to varying spectral distributions. In this context the transforming capacities of both square and row patterns can be understood.