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Morphological and histochemical examination of the blood and connective tissue of the freshwater snail Lymnaea stagnalis injected with various types of foreign particulate materials has shown the existence of free as well as fixed phagocytic cells. The morphology of the fixed phagocytes is described, and the phagocytic system of the snail is compared with that of other molluscan species.

By means of immunohistoperoxidase techniques and the use of HRP-anti-HRP complexes, follicular dendritic cells in chicken spleen can be characterized both at the light-microscopical and ultrastructural level. In contrast to findings in mammals follicular dendritic cells in chicken spleen exhibit evident acid-phosphatase activity and possess considerable numbers of primary lysosomes. After intravenous injection of immune complexes a transient immune complex-trapping occurs in the peripheral parts of the Schweigger-Seidel sheath. The immune complextrapping cells in the Schweigger-Seidel sheath and germinal centre show an identical enzyme histochemical pattern and only minor differences in ultrastructural characteristics.