Summary
Free nerve endings are abundant in the distal epithelium of the tentacles of Arion ater Four ultrastructurally distinct types of ending are identified from serial sections. The Type 1 free nerve ending bears a distal cup from which arise short microvilli and a few cilia. Different free nerve endings in this grouping may show considerable individual variation. The Type 2 free nerve ending bulges slightly at its distal surface. From its surface arise short microvilli and numerous cilia. The Type 3 and Type 4 free nerve endings are unusual since they bear only long microvilli, cilia being absent. In the Type 3 these microvilli are few. In the Type 4 they are numerous and form a cluster at the dendrite tip. In the distal epithelium of the inferior and superior tentacles approximately 10% of the free nerve endings are Type 1 8% Type 2 and 80% are Type 3, Type 4 being rare. It is tentatively suggested that the Type 1 ending is mechanoreceptive and the Type 3 ending is chemoreceptive.
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The authors wishes to thank Dr. D. K. Roach and Mr. T. Davies for their helpful advice and Drs. D. Graham and U. Zylstra for proof-reading the manuscripts. This research was carried out during the tenure of an S.R.C. research studentship.
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Wright, B.R. Sensory structure of the tentacles of the slug, Arion ater (Pulmonata, Mollusca). Cell Tissue Res. 151, 245–257 (1974). https://doi.org/10.1007/BF00222226
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DOI: https://doi.org/10.1007/BF00222226