Nutritive phagocytosis in animal cells

Summary Nutritive phagocytosis in the hydroid Clava squamata was studied with the electron microscope, using carbon particles of 0.6 as an indicator.An early step in phagocytosis is the transformation, in many cells, of the free border from a type with cylindrical microvilli to one with a complicated system of cytoplasmic folds.Particles fixed at the actual stage of ingestion are found (a) between two cytoplasmic folds, (b) between a fold and a relatively straight portion of the cell surface, or (c) in a depression of an otherwise straight portion of the cell surface.Ingested carbon particles were always found enclosed by a membrane, with a layer of moderate electron density between the carbon particle and the membrane.The ingested carbon particles are localized apically in small vesicles each containing one particle (interpreted as primary phagocytic vesicles) or at deeper levels of the cell, in larger vesicles containing many carbon particles (interpreted as secondary phagocytic vesicles).Other cytoplasmic changes during phagocytosis relate to the distribution of mitochondria and the occurence and distribution of flattened vesicles of a characteristic appearance.With the technical assistance of Birgitta af Burén.Financial support from Swedish Natural Science Research Foundation is gratefully acknowledged.