Ultrastructure of the parathyroid gland of fresh-water turtles.

The parathyroid glands of fresh-water turtles (Pseudemys scripta and Chrysemys picta) are composed of cords of cells in which dark and light variants of chief cells and occasional oxyphil cells can be distinguished. Cytoplasmic granules measuring about 0.3-0.4 μm and all the cellular organelles associated with protein and carbohydrate synthesis can be seen in both dark and light chief cells; the cytoplasm of oxyphils is packed with mitochondria which obscure other organelles. An unusual feature of the dark chief cells is the presence of crystalline-like material within parallel arrays of cisternae of rough endoplasmic reticulum. A similar crystalline-like structure is seen occasionally within some cytoplasmic granules.