1911 Encyclopædia Britannica/Protista

PROTISTA, a name invented by Ernst Haeckel (Generelle Morphologie der Organismen, 1866) to denote a group of organisms supposed to be intermediate between the animal and vegetable kingdoms. As knowledge advanced the precise limits of the group shifted, and Haeckel himself, in successive publications, placed different sets of organisms within it, at one time proposing to include all unicellular animals and plants, making it a third kingdom equivalent to the animal and vegetable kingdoms. Partly because the term represented an interpretation rather than an objective set of facts, the word Protista has not been generally accepted for use in classification, and, whilst recognizing that the limits of the animal and plant kingdoms are not sharply defined, modern systematists refrain from associating these doubtfully placed organisms simply because of the dubiety of their position. (See Protozoa.)