Seasonal ultrastructural changes in the pineal gland of the migratory Canada goose

Ultrastructural changes in the pineal gland were studied in relation to migration, breeding and moult. Sizes of pinealocytes and that of their nuclei were greatest in the Spring premigratory and postmigratory, and moult phases. The ratio of nuclear size to cell size was greatest for the breeding phase and lowest for the Fall premigratory and postmigratory phases. The Golgi complex was most prominent during premigratory and breeding phases. Mitochondria which were numerous in all phases except during moult, were markedly enlarged during breeding and Fall premigratory phases. Dense-core vesicles were predominant in Spring postmigratory and moult phases. In glial cells, lipoid inclusions were abundant in Spring premigratory and postmigratory, and breeding phases. Glycogen granules were abundant in Spring postmigratory, breeding and moult phases. Large vacuoles were present in Fall premigratory phase. Lamellar membraneous whorls were often present near luminal spaces during Spring premigratory and postmigratory, and breeding phases. The endothelial cells of pineal capillaries during Spring and Fall premigratory phases, contained numerous vesicles, some of which were freely dispersed in the cytoplasm while others were fused to the cell membrane, suggestive of transendothelial transport of vesicular substances.