Structure and ultrastructure of the pituitary gland in the sea lamprey, Petromyzon marinus at different stages in its life cycle.

The structure and fine structure of the pituitary gland in the sea lamprey, Petromyzon marinus L., are described at all major stages in the life cycle. Synthetically active adenohypophysial cells are evident in even the smallest ammocoetes examined (body length 2.5 cm). An attempt is made to correlate changes in the activity of pituitary cell types with biological events. In the neurohypophysis a single fibre type was discriminated in electron micrographs. This contained electron-dense cytoplasmic granules 800 to 1600 A in diameter.