Pituitary cysts in the sea lamprey of the Great Lakes, Petromyzon marinus L.

Large epidermal cysts that occur in the adenohypophysis of spawning lampreys develop as a consequence of destructive invasion of the parenchyma by an epithelium derived from the same anlage as the medial nasopharyngeal duct. The lumina of the cysts contain a carbohydrate-rich secretory material which is a mixture of epithelial mucins. An array of histochemical methods was used to show the kinship of the cysts with the mucin-secreting epidermis of the duct. These cysts appear to be unique to the cyclostomes and to have no obvious adaptive benefit.