An ultrastructural study of the mucous membrane of the small intestine in the toal (Bufo melanostictus) has shown that in the epithelium, besides the typical epithelial lining cells, non-epithelial cell types, including lymphocytes, macrophases, plasma cells, eosinophils and neutrophils are present. These non-epithelial cell types are also encountered in the lamina propria, which also contains numerous fibroblasts, smooth muscle cells and mast cells. The ultrastructural features of toad intestinal mucous membrane thus resembles that in mamals in many of its features, The intraepithelial localization of macrophages and of mature plasma cells is unusual. The observations suggest that the toad intestinal mucous membrane may function as a lymphoepithelial organ.
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