PAET I. 



OEOORAPHIOAL DISTRIBUTION. 



I. 



General principles of zoogeography. — ^Faimas of isolation. — Kelatlons of past 

 and present faunas. 



EvEKTWHEBB upon the surface of the earth we meet with mani- 

 festations of animal life. The desert wastes, no less than the trop- 

 ical jungles, the bleak ice-flelds of the frozen north, and the most 

 elevated mountain-summits — all have their faunas. The abyss of 

 the sea, no less than its surface, contributes its quota to the animal 

 world ; and in the atmosphere all around us, from the lowest stra- 

 tum not unlikely to the highest, the germs of the organic universe 

 lie everywhere scattered about. In what precise form or guise this 

 life first manifested itself, or how inert matter became endowed 

 with that potentiality which we recognise in vital energy, it seems 

 hopeless to attempt to determine. True science takes cognisance 

 of both fact and theory, but illusory speculation, whose ground- 

 work is a simple outgrowth of the imagination, must find a rest- 

 ing-place without its domain. 



No one who has paid the smallest amount of attention to the 

 facts of nature as they present themselves can have failed to notice 

 certain peculiarities in the way of the distribution of life, which 

 do not always admit of an immediate or of a satisfactory inter- 

 pretation. Why, for example, one piece of country should differ 

 so essentially in its faunal aspects from another whose physical 

 characteristics are practically identical with its own ; why the sec- 

 ond should differ from a third, and this, again, from a fourth — may 

 not appear comprehensible. Nor any the more comprehensible 

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