| Popis: |
The epidermal receptor cells and their distribution throughout the body surface of Lymnaea stagnalis and Biomphalaria pfeifferi were studied by means of light and electron microscopic techniques. The investigations reveal general agreement between the two species. The receptor cells are primary sensory nerve cells with the cell bodies lying below the epidermis. The subepithelial cell bodies are frequently grouped together forming small ganglia, particularly in rich sensory regions, such as the lips and the tentacles. Dendrites extend from these sensory cell bodies between the epidermal cells and form free nerve endings at the surface of the epidermis. Six different types of free nerve endings are distinguished on the basis of the number of cilia present and on the length and structure of the cilia roots. A survey of the distribution of the sensory cells revealed that they are restricted primarily to the tentacles, lips, front edge of the foot, pneumostome and mantle edge, although they are also present in the dorsal and lateral surface of the foot. No free nerve endings were found in the dorsal head epidermis. Only one type of nerve ending was found to have a specific localization, whereas the other types have a general distribution. Although it is difficult to determine the function of the different types of free nerve endings in an ultrastructural study, some suggestions are made on the basis of morphological comparisons with receptor cells in other species and also on the basis of behavioral and physiological experiments which have been performed on L. stagnalis. |
