The morphology of the trout, Salmo gairdneri Richardson, thymus: some practical and theoretical considerations

An electron microscope study of the thymus in trout, Salmo gairdneri, showed that the membrane separating the thymus gland from the extenal water current was not specialized, but merely a continuation of the pharyngeal epithelium. This is discussed in relation to the evolution of the thymus in vertebrates, and to the possible effects on the thymus during hyperosmotic infiltration, a technique used for immunization.