CHAPTER VI 



THE I^UMEEICAL DISTEIBUTION OF SPECIES IN RELATION" » 



TO EVOLUTION 



The rather lengthy account I have given of the numerical 

 distribution of species over both small and large areas, and 

 in special relation to latitude and to climate, has a very def- 

 inite object. In the first place, this distribution constitutes 

 the primary and fundamental fact in the relation of species 

 to the whole environment — it is, in fact, the broadest and 

 most simple expression of that relation, and is thus a proper 

 subject of inquiry in any general view of the world of life. 

 Yet it has been strangely neglected both by botanical and 

 zoological writers; and the largest and oldest collections of 

 plants and animals in all countries have been so dealt with as 

 to afford material for almost every form of biological research 

 except this one. 



The mere enumeration of the numbers of species^ named or 

 unnamed, with the localities of each specimen, in the great 

 national collections of the world, would have afforded all the 

 materials for such comparisons as I have here endeavoured to 

 make. And if the facts were recorded in card-catalogues, 

 instead of in the usual forms, there would be such a demand 

 for sets of these cards applying to special groups and definite 

 geographical areas, by most students or collectors, that the cost 

 of such catalogues would be more than repaid. 



This numerical relation of the various groups of organisms 

 in different areas or geographical divisions of the earth has 

 the further advantage of being interesting and intelligible to 

 the general reader, as it involves the use of hardly any tech- 

 nical terms, and is therefore especially suitable for a work 



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