1834 The natural history of animalcules : containing descriptions of all the known species of Infusoria : with instructions for procuring and viewing them London, Whittaker and Co.
organisms including bacteria, Archaea, Protista, and associated viruses, exploring and discovering unknown microbial diversity, and placing that knowledge into ecological and evolutionary contexts.
In 1938, Herbert Copeland resurrected Hogg's label, arguing that Haeckel's term protista included anucleated microbes such as bacteria, which the term "Protoctista" (literally meaning "first established beings") did not.
This system was preceded by Haeckel's three-kingdom system: Animalia – Plantae – Protista