128 A NATURALIST IN TASMANIA ch. 



mining the mutual relationships of the creatures 

 dealt with, and the probable line of their descent 

 from one another or from some common ancestor, 

 and furthermore we should know sufficient facts 

 about their habits and economy to be able to 

 judge of their capacity for dispersion and for 

 surmounting barriers, whether of temperature, 

 seas, or mountains. In fact, a complete theory 

 accounting for the geographical distribution of 

 animals and plants would include so many of 

 the essential facts with which Biology deals, as 

 to imply a fairly comprehensive statement of the 

 historical process of evolution. 



The settling and opening up of Australia at 

 the beginning of the nineteenth century revealed 

 a new world of surpassing interest to the naturalist, 

 a world where unknown and unimagined forms 

 of life constituted the commonest and most 

 dominant part of the inhabitants, where every 

 living thing, including man, seemed to have been 

 cut off and isolated from the rest of the world 

 at some remote period. 



Our present knowledge of Australian natural 

 history substantiates the view that the animals^ 

 and to some extent the plants, of this part of 

 the world represent remnants of a population 

 which once ranged all over the northern hemi- 

 sphere, and which, being cut off in early times 

 from the rest of the world, has branched out and 

 diverged in all directions, free from competition or 

 intermixture with the newer and more highly 



