Recent investigations on the nutrition of the ciliary-feeding bivalves indicate that, although many varieties of organic and inorganic substances are ingested, most of the actual food is assimilated by the intracellular digestion of very small cells and particles. This is accomplished mainly by the phagocytic cells of the digestive organ (digestive diverticula, or "liver"), but it is aided to a small extent by migratory phagocytic cells in the lumen of the alimentary canal....