There is great danger of arguing in a circle. It is one of the most difficult tasks to decide in cases of great resemblance of groups of animals between their being due to direct affinity or to heterogeneous convergence, or parallel development. It is the morphologist who is ultimately responsible for the establishment of faunistic regions, not the systematist, least of all he who accepts an elaborate classification, and then mechanically, mathematically, by lists of genera and species, maps out the world. Let us take an example. The Neotropical region and Madagascar, but not Africa, are supposed to be faunistically related to each other. In both namely occur _Boa_ and _Corallus_ amongst snakes, Dendrobatinae amongst Ranidae, and of the Insectivora _Solenodon_ in Cuba, _Centetes_ in Madagascar. More cases can no doubt be found which would strengthen this resemblance, perhaps in support of the startling view that Madagascar and South America have received part of their fauna from the famous Antarctica. But the value of the Insectivores has been disposed of by their recognition as an extremely ancient group, or as a case of convergence, and the two genera are no longer put into the same family as Centetidae. The Dendrobatinae (_Mantella_ in Madagascar, the others in South America) are decidedly not a natural group, but an instance of very recent convergence (cf. p. 272). About the members of the ancient Boidae we do not feel quite so sure. It is therefore advisable to eliminate for zoogeographical purposes groups about which there can be any reasonable doubt, otherwise we may argue that certain genera must constitute a very old family, because they are now restricted to widely {72}separated countries, or on the strength of their distribution we may conclude that the genera in question cannot be related to each other, and do not belong to the same sub-family or family as the case may be. Such groups are the Engystomatinae and the genus _Spelerpes_; amongst reptiles the Eublepharidae, Helodermatidae, Anelytropidae, Ilysiidae, Amblycephalidae.