Animal toxins are not to be understood as substances of random occurrence; they are of great importance in ecology. The venom-secreting organs have developed in a wide variety of ways and serve either as an offensive weapon or for protection against enemies. Accordingly, we may distinguish between actively venemous and passively venemous animals. There are other animals that are toxic rather by chance and due to extraneous factors; these we may call poisonous animals. Research into animal toxins is important from both the chemical and the biological points of view. In addition to basic knowledge, we may hope for interesting phylogenetic results from such research.