Jovan Hadži theories of animal evolution. He devised a system of classification in which he divided the animal kingdom into six phyla: Protozoa, Parazoa, "Ameria" (animals with no segments), "Oligomeria" (animals with few segments), "Polymeria" (animals with many segments) and Chordata. His choice of characters important for classification was generally discredited by his contemporaries, and the system was never accepted by zoologists. However, due to its simplicity, the system was widely used in science education in former Yugoslavia. His other major theory was that of the origin of metazoa - he developed an existing hypothesis stating that the first multicellular animals resembling
Worm were one of three kingdoms, divided into the classes of Vermes, Insecta, Pisces, Amphibia, Aves, and Mammalia. Since then the last four have all been subsumed into a single phylum, the Chordata, while his Insecta (which included the crustaceans and arachnids) and Vermes have been renamed or broken up. The process was begun in 1793 by Lamarck, who called the Vermes "une espèce de chaos" (a sort of chaos) and split the group into three new phyla, worms, echinoderms, and polyps (which contained corals and jellyfish). By 1809, in his "Philosophie Zoologique", Lamarck had created 9 phyla apart from vertebrates