The human crista ampuilaris was studied more closely in relation to its shape, the extension of its sensory epithelium and nerve supply. These findings were compared with those from specimens of shark, frog, alligator, cat, pigeon and monkey. The crista is semilunar in shape, the side parts have a greater area of neuroepithelium, and the nerve supply to the side parts is accordingly denser. This underlines the functional importance of the sliding movements of the cupola over the hair cell region, the "subcupolar space" was studied by removing the cupola and examining the morphological changes. This showed: (1) that 1/2 hour after the operation the hairs appear freely floating in the endolymph, (2) that after some hours the spaces between the hairs are filled with eosinophilic "globules", which could be traced to the increased secretory activity of the "transitional epithelium" at the slopes of the crista, (3) that after some days or weeks, this layer of "globules" is lifted towards the tips of the hairs, presumably by some secretion from the supporting cells of the crista. These activities are assumed to play an important part in the formation of the "subcupolar space".