Abstract
A recent editorial inNature(Anon., 1951) on current problems in parasitology has emphasized the importance of the cultivation of parasitic organisms free from their hosts and from other species. The increased interest of workers in this type of problem, and their expanded efforts with helminths (as reviewed by Read, 1950, for helminths in general, and by Hobson, 1948, for the nematodes), which have so far almost completely resistedin vitrocultivation through whole life cycles,‡ make highly desirable an assessment of the nomenclature to be used in describing various relationships between organisms, both in nature and in the laboratory.