Summary
The peripheral nervous system of the polyclad flatworm Notoplana acticola is described from electron microscopic observations. There are two components, a subepithelial system and a submuscular plexus. The subepithelial system lies among muscle cells beneath the basement membrane of the epithelium. Axons and processes containing clear or dense-cored vesicles were found. The subepithelial system is in the form of a feltwork of fibers rather than a nerve-net. The submuscular plexus has both specialized and primitive aspects to its organization. In the former category are sheathed axons and complex synaptic configurations while the latter can be seen in the numerous naked axons, somata lying deep in the nerve tissue and islands of neuropil scattered along the nerve tracts.
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Koopowitz, H., Chien, P. Ultrastructure of the nerve plexus in flatworms. Cell Tissue Res. 155, 337–351 (1974). https://doi.org/10.1007/BF00222810
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DOI: https://doi.org/10.1007/BF00222810