The origin of the otoconia in the rat.

The transitional zone of the saccule and the utricle--has been studied by transmission electron microscope in rats, days before birth. A noticeable secretory activity has been observed in their cells as well as the presence of inorganic spicular bodies that have also been observed in the lumen, some of them integrated into the otoconia. These findings were not seen in adult animals. It is assumed that both organic and inorganic components of the otoliths are produced in a critical period of the embryonal development in the transitional cells.