The response of retinae of the Japanese common squid (Todarodes pacificus Steenstrup) was recorded in relation to various light intensities. In the light-adapted eye of common squid, the black pigment ascends to the external limiting membrance of the retina. Conversely, in the dark-adapted eye the black pigment descends toward the center of the black pigment layer. To express the degree of adaptation, the authors give the ratio of the height (thickness) of the black pigment to the total height (thickness) of the retina as a percentage (%)
