Ink particles injected into the hemolymph of the American lobster (Homarus americanus), spiny lobster (Panulirus interruptus), crayfish (Procambarus clarkii), and ridgeback prawn (Sicyonia ingentis) were rapidly removed from circulation, and most were sequestered within nodules in the gills. The morphology of the gills and the nodules were examined from the time of injection until the following molt. The process by which ink was cleared from the gills was the same in all four species. Nodules formed within 10 min after injection and were composed of hemocytes loosely attached to one another and binding small quantities of ink. Within one week, nodules became spherical and more compact with accumulations of ink surrounded by layers of flattened hemocytes. By one month, hemocytes in the nodules had degenerated leaving melanized masses which lay between the gill epithelium and the exoskeleton. Following molting, the gills of both trichobranchiate and dendrobranchiate species were clean or had very reduced numbers of nodules, and melanized masses were seen attached to the inner surface of the shed exoskeletons. A similar mechanism for cleaning the gills has been reported in crustaceans infected with parasites and in necrotic gill tissue caused by exposure to toxic heavy metals. We, therefore, suggest that the ability of the gill epithelium to wall off foreign material so that it is lost during the following molt is a general mechanism to prevent occlusion of the gill and maintain its role in ion regulation and respiration.