A study of the ultrastructure of the intestine of Ancyclostoma caninum reveals several new features: The presence of glycogen, the presence of intramitochondrial crystalloids, the fine structure of pigment granules, and the differences between mid- and hindgut. Each intestinal cell is differentiated into five zones: The striated border, the terminal web, the central zone, the reticular zone, and the basal lamina. The central zone contains the majority of organelles and inclusions. These include mitochondria, ribosomes, endoplasmic reticulum, Golgi complexes, lysosome-like granules, pigment and glycogen granules. Numerous pigment granules and many mitochondrial crystalloids are observed in the anterior portion of midgut. The posterior midgut and hindgut are rich in ribosomes and lysosome-like granules, but contain few or no pigment granules. These differences may reflect a functional differentiation between mid- and hindgut. Pigment granules are polymorphic and are of three types. The predominant type in the anterior midgut has a perforated shell and a dense amorphous core. A few exhibit concentric lamination and a lesser number have a particulate structure. Their polymorphism suggests that they are in a dynamic state, and may change from type to type. © 1969.
