Ultrastructure of the Redia of Cryptocotyle lingua

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Abstract
Electron micrographs of the redia of Cryptocotyle lingua show many highly flexible, ribbonlike folds extending from the epithelial cells of its saccate intestine into the lumen. Nutritive phagocytosis is suggested by the entrapment of food globules by curved intestinal folds which loop to coalesce with the apical surface of the gut cells. Droplets impounded by these processes may then sink into the cytoplasm of the intestinal cells as vesicle. The body surface of the redia is characterized by the presence of numerous, broad, cytoplasmic projections, the integumental folds or flaps. It is proposed that the integumental folds engulf nutrients by pinocytosis in a manner similar to that indicated above for intestinal folds. Cavitations of the apical integumentary membrane, sparsely present along the outer surface of the redial body, are suggestive of micropinocytosis. Mitochondria, membrane-bounded vesicles, and glycogen-like granules are found in the integument. Circular and longitudinal muscle cells contain only beta glycogen particles, whereas both alpha and beta varieties of glycogen are present in parenchymal cells.