BIOLOGY 



arisen in the course of evolution, is still one of the 

 major problems of Biology and one for which it is 

 peculiarly the duty of the systematist to find a 

 solution. 



The next subject in our scheme of classifica- 

 tion is the Geographical Distribution of living 

 organisms, or Biogeography, in connection with 

 which we again find a copious literature and a high 

 degree of specialisation. The interest attached 

 to this subject is twofold. On the one hand the 

 distribution of plants and animals over the face 

 of the earth throws considerable light on the 

 geography of the past, and on the other it affords 

 much valuable evidence with regard to organic 

 evolution. The latter point of view is the one 

 which alone concerns us now, and the keynote 

 of the whole argument is supplied by the 

 phrase * adaptive radiation,' which has lately 

 come so much into vogue amongst writers on 

 the subject. This phrase expresses the broad 

 conclusion that the great groups, of the animal 

 kingdom at least, have radiated from their 

 original homes in various directions, adapting 

 themselves in the course of their migrations 

 to new conditions of life, and thus giving rise 

 to new types. No conclusion could agree 

 more competely with the theory of organic 

 evolution. 



i 129 



