CHAPTER V. 



CLASSIFICATION AS AFFECTING THE STUDY OF GEOGRAPHICAL 



DISTRIBUTION. 



A little consideration will convince us, that no inquiry into 

 the causes and laws which determine the geographical distribu- 

 tion of animals or plants can lead to satisfactory results, unless 

 we have a tolerably accurate knowledge of the affinities of the 

 several species, genera, and families to each other; in other 

 words, we require a natural classification to work upon. Let us, 

 for example, take three animals — a, b, and c — which have a 

 general external resemblance to each other, and are usually 

 considered to be really allied ; and let us suppose that a and b 

 inhabit the same or adjacent districts, while c is found far away 

 on the other side of the globe, with no animals at all resembling 

 it in any of the intervening countries. We should here have a 

 difficult problem to solve ; for we should have to show that the 

 general laws by which we account for the main features of 

 distribution, will explain this exceptional case. But now, sup- 

 pose some comparative anatomist takes these animals in hand, 

 and finds that the resemblance of c to a and b is only superficial, 

 while their internal structure exhibits marked and important 

 differences ; and that c really belongs to another group of 

 animals, d, which inhabits the very region in which c was 

 found — and we should no longer have anything to explain. 

 This is no imaginary case. Up to a very few years ago a 

 curious Mexican animal, Bassaris astuta, was almost always 

 classed in the civet family (Viverrida3), a group entirely con- 



