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 , 5, 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 (Yiverridse), a group entirely 
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