The perineural sheath in the urodele amphibian

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Abstract
The perineural epithelial cells of the peripheral nerve sheath in Triturus are elongated flat cells with long and thin cytoplasmic processes. Structural characteristics of the processes include a relative absence of common cytoplasmic organelles of the periniuclear cytoplasm but an abundance of vesicular profiles similar to fully formed pinocytotic vesicles. Unlike pinocytotic vesicles, vesicles of the processes often contain an 8‐nm thick filament attached to their cytoplasmic face. Vesicles are also interconnected by similar filaments or by tubules. In addition, almost all vesicles appear to have openings at the cell surface, a feature not seen for pinocytotic vesicles. The concentration of exogenous peroxidase in the vesicles, and the subsequent appearance of peroxidase in the endoneural fluid, myelin sheath and axon, support the notion that the vesicles function in the exchange of substances between extraneural and endoneural fluids.