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
Lattice of subgroups of the form Z × Z, generated by pairs of order-two elements. The lattice formed by these ten subgroups is shown in the illustration. This example also shows that the lattice of all subgroups of a group is not a modular lattice in general. Indeed, this particular lattice contains the forbidden "pentagon" "N" as a sublattice. For any "A", "B", and "C" subgroups of a group with "A" ≤ "C" ("A" subgroup of "C") then "AB" ∩ "C" = "A(B ∩ C)"; the multiplication here is the product of subgroups. This property has been called the "modular property of groups"