QUANTITATIVE STUDIES ON PIGMENT MIGRATION AND LIGHT SENSITIVITY IN THE COMPOUND EYE AT DIFFERENT LIGHT INTENSITIES

Comparative electrophysiological and histological studies were made on the functional significance of the secondary iris pigment migration for the sensitivity of the eye in the noctuid moth Cerapteryx graminis. The pigment position at different adapting light intensities was studied as well as the influence of different positions on the sensitivity of the eye. Adapting light intensities above a certain value hold the pigment in light position. At a 3 log units lower intensity the pigment is brought into dark position and at light intensities between these limiting values the pigment attains intermediate positions. The results indicate that at light intensities between the limiting values the pigment shifts closely follow the changes in intensity of the environmental light. With the pigment in dark position the eye is about 1000 times more sensitive than when the pigment is in light position, there being a close relationship between the sensitivity of the eye and the position of the pigment at intermediate positions.