Describing the migrations and movements of the cod, Gadus callarias L., in the Barents Sea, Trout (1957) suggested that the immature fish carry out a false spawning migration. ‘The pattern of migration of the immatures is basically similar to that of the matures…with increasing age, the immatures’ southerly winter migration approached in length that of the mature cod, as if, in the years immediately prior to maturity they were making a “dummy run” towards the spawning ground.' The seasonal migrations of both the adult and immature cod have been related to changes in the activity of the thyroid gland in this fish (Woodhead, 1959). During the spring of 1956 and 1957, collections of thyroid glands from immature cod were made at stations from Bear Island to the Norwegian coast. It was hoped that a study of these glands might demonstrate further the relationship of the activity of the thyroid gland to the migration of the fish.