GEOGRAPHICAL DISTRIBUTION OF VERTEBRATE ANIMALS. 403 



them from the parent species, and which will in time so 

 differentiate them, by developing their peculiarities, that they 

 may fairly be regarded as distinct species, though opinions will 

 always differ as to the point at which this separation may be 

 considered to have taken place. These and many other inte- 

 resting points which might be elucidated by the successful 

 carrying out of the following scheme, will readily occur to the 

 reader. 



The present is, I think, a very opportune time for undertaking 

 the work, which may be said to have long been " in the air"; yet 

 it may be doubted whether, until the last few years, the informa- 

 tion available has been sufficient to admit of its accomplishment 

 with anything like completeness. 



It will be obvious that the value of any such scheme as 

 that herein sketched out will depend almost entirely upon its 

 accuracy, and that, as the work progresses towards absolute 

 completeness (though this is, of course, practically unattainable), 

 the value will increase in a still more rapidly increasing ratio ; 

 for, in any such scheme, there would be comparatively little value 

 in the details, or in full information from a restricted area, or in 

 the complete mapping of the distribution of a few species only 

 throughout the world ; but considerable value would attach to 

 such broad generalizations as might be drawn from the carrying 

 out of a comprehensive scheme of the kind. Thus a series of maps, 

 showing the distribution of all species inhabiting any country 

 having political boundaries (let us take France for example), 

 within that country only, would be so incomplete as to have but 

 little value, except as a small contribution to a vastly larger 

 scheme. Any such work, if undertaken with the idea that it was 

 an end in itself, would merely show the absurdly parochial view 

 which is still so often taken of the study of natural science. If 

 the work were extended so as to show the distribution of French 

 species, not only in France, but throughout the world, it would 

 at once be placed on a more natural and rational basis ; but 

 we seem scarcely to reach a stage of even approximate com- 

 pleteness, from a natural point of view, until we have fully 

 mapped out the distribution throughout the world of all the 



I species inhabiting any one of the great natural regions (the 

 Palsearctic, for example) into which naturalists have divided the 

 world. It seems to me that these broad generalizations, on which 

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