The morphology of the amphibian endolymphatic organ

An extensive survey of the anatomy of the endolymphatic organ (i.e., endolymphatic sac and duct) has been made on thirty‐four species of amphibians. The histological structure is similar throughout the group; the sac being formed of cubical cells, which grade into the columnar cells of the duct. A part or the whole of the duct is formed of peculiar ‘ependyma‐like’ cells. The organ typically arises from the sacculus, extends to the endolymphatic foramen by which it enters the endocranial cavity. Here the sac‐like expansion of the organ lies in the extradural space. Six morphological types of endolymphatic organ may be recognized in the Amphibia. The development of the endolymphatic organ of four of these types has been followed. The structure in each case may be considered to have reached its definitive condition at the time of metamorphosis. The types of sac structure cannot be readily correlated with any habit of the animals possessing them. A discussion is given of the homology, comparative morphology, and function of the organ throughout vertebrates.