OK ZOOLOGICAL FOCI 



145 



There arc two theories, which have mainly divided 

 the opinions of naturalists. The first supposes that the 

 existing races of animals were of simultaneous creation 

 at a common centre or focus, from which they have 

 spread over the whole earth ; the other considers that 

 there were several distinct centres or foci, from which 

 the species radiated into — and thus formed, the zoolo- 

 gical circles or regions which are now apparent. The 

 first supposition, though possible, is seen at once to be 

 attended with many physical difficulties, and has but few 

 supporters ; while the second, commends itself to the 

 minds of almost all. In surveying the zoology of the 

 earth, we find groups of distinct animals, of the different 

 classes, occupying regions which are defined by natural 

 boundaries, and limited to these regions alone ; and the 

 discovery of new continents and islands has, in every 

 case, revealed animals peculiar to each of them. The 

 existence of distinct zoological regions has hence come 

 to be an axiom in the philosophy of zoology, and the 

 theory of distinct foci of animal origin has thus been 

 greatly fortified. But in all the speculations of natural- 

 ists on this subject, and in all their attempts to deduce 

 the limits of the various regions, from the actual distri- 

 bution of animals, attention has been given almost solely 

 to the large animals, and mostly to the vertebrata, and 

 consequently the regions as laid down by authors, are co- 

 extensive with the wide range of these species. It is 

 manifest, however, that the ranges of the different classes 

 of animals differ very much among themselves, and that 



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