CHAP. XVIII JAPAN AND FORMOSA 



410 



The distribution and affinities of the animals of con- 

 tinental islands thus throws much light on that obscure 

 subject — the decay and extinction of species ; while the 

 numerous and delicate gradations in the modification of 

 the continental species, from perfect identity, through 

 slight varieties, local forms, and insular races, to well- 

 defined species and even distinct genera, afford an over- 

 whelming mass of evidence in favour of the theory of 

 " descent with modification." 



We shall now pass on to another class of islands, which, 

 though originally forming parts of continents, were 

 separated from them at very remote epochs. This 

 antiquity is clearly manifested in their existing faunas, 

 which present many peculiarities, and offer some most 

 curious problems to the student of distribution. 



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