An electron microscopic study of the otolithic maculae of the lamprey (Entosphenus japonicus).

The sensory epithelium of the otolithic maculae from the inner ear of the lamprey (Entosphenus japonicus) was studied under the scanning and transmission electron microscope. Two different types of sensory hair cells were discerned and each had a patterned distribution over the various maculae. One type of hair cell had 20-30 short stereocilia and one long kinocilium on its surface. The other type exhibited much longer stereocilia which were arranged in graded heights (organ-pipe configuration) from one side of the cell to the other. So-called striated organelles were found in the cytoplasm of both types of sensory cells. These striated organelles exhibited periodic electron-dense and less dense striations of 170 mum extending from the cuticular plate down to the basal portion of the cell. Generally, this organelle was found in profusion in the sensory cells with long hair bundles but rarely found in the other type of cells.