Ultra structural differentiation and the renewal of the receptor cells in the sensory epithelia of the lips and the anterior tentacles of the snail Helix pomatia.

Renewal and ultrastructure of the receptor cell bodies in the sensory epithelia of the lips and anterior tentacles of helix pomatia were studied by light microscopic autoradiography and electron microscopy. The autoradiography revealed continuous mitosis in the receptor cell mass of both organs. After a short survival time (30 min) following the 3H-thymidine injection only heavily labelled cell pairs could be located predominantly at the periphery of the sensory lobules. After a longer survival time lightly labelled cells appeared and gradually became dominant. In the sensory lobules different types of cell bodies could be distinguished with light, medium dense, or dark cytoplasm, and with specific ultrastructural features. Cell bodies with medium dense cytoplasm were dominant while dark cells could be observed scarcely in the lobules. The continuous mitosis and the ultrastructural differences of the receptor cell bodies suggest that the dark receptor cells may correspond to the heavily labelled cells, while the light receptor cells may represent the early state of maturation. The medium dense receptor cells represent the mature receptor cell bodies. The present observations show that the continuous renewal and maturation of the receptor cells is a general phenomenon in the sensory epithelia of the snail.