The geographical distribution of animals, with a study of the relations ...

—CHAPTER V.CLASSIFICATION AS AFFECTING THE STUDY OF GEOGRAPHICALDISTRIBUTION.A little consideration will convince us, that no inquiry intothe causes and laws which determine the geographical distributionof animals or plants can lead to satisfactory results, unlesswe have a tolerably accurate knowledge of the affinities of theseveral species, genera, and families to each other; in otherwords, we require a natural classification to work upon.for example, take three animalsLet us,a, b, and c—which have ageneral external resemblance to each other, and are usuallyconsidered to be really allied ; and let us suppose that a and binhabit the same or adjacent districts, while c is found far awayon the other side of the globe, with no animals at all resemblingit in any of the intervening countries.We should here have adifficult problem to solve ; for we should have to show that thegeneral laws by which we account for the main features ofdistribution, will explain this exceptional case. But now, supposesome comparative anatomist takes these animals in hand,and finds that the resemblance of c to a and b isonly superficial,while their internal structure exhibits marked and importantdifferences ; and that c really belongs to another group ofanimals, d, which inhabits the very region in which c wasfound— and we should no longer have anything to explain.This is no imaginary case. Up to a very few years ago acurious Mexican animal, Bassaris astuta, was almost alwaysclassed in the civet family (Viverrida3), a group entirely con-