References to the presence of " Infusoria" within the utricles of Utricularia occur in several publications on insectivorous plants, but no one has hitherto studied the interrelations of these protozoa and the plants. The situation suggests various questions, such as (I) are the protozoa intruders that act as scavengers feeding on the dead bodies of other captives; (2) are they captured by the plants and used as food; (3) are they adventitious residents that slowly starve to death within their prison-like walls; or (4) are they "normal" inhabitants, possibly differing in