Haeckel distinguished between ≪Phylogenie≫ and ≪Ontogenie≫, as opposed to ≪Phylogenese≫ and ≪Ontogenese≫. The former concepts are supposed to deal with the history of phyletic and biontic (i.e. individual) development, respectively, while the latter are concerned with the mechanisms of these processes. Haeckel's terminological distinction can no longer be upheld, ≪phylogeny≫ and ≪phylogenesis≫ are currently used as synonyms, and the same holds for the other pair of words.