A lectin‐membrane receptor system is described during capsule formation in the mantis shrimpSquilla mantis, as a model for studying immunological defense in arthropods. The following topics, in particular, are emphasized: the importance of induced lectins in recognition of ≪self≫ by hemocytes; the biochemical characteristics of oligosaccharides of foreign bodies in the mechanism; the importance of monoclonal antibodies in purification of lectins and their localization.