Studies of diurnal vertical migration in the polar seas are of special interest since we arc able to make observations in nature (without the possible drawbacks of laboratory experiments) of the behavior of animals under the widely varying light conditions that prevail during different seasons. Thus, during the polar summer it is possible to investigate the diurnal migration under conditions of uninterrupted daylight, during the polar autumn and spring under changing conditions of alternating days and nights, and finally in winter under conditions of permanent darkness. At present a series of special diurnal stations are available, taken mainly in the Barents Sea, as well as in the White Sea. Unfortunately, owing to weather conditions, no diurnal stations have been obtained as yet in winter and spring.