Eastward transport 21 1 



The reasons for its poor effect, p. 214 - Another explanation, p. 216. 



The economic importance of introduced animals 218 



On the minimum size of a viable population 223 



Bibliography 225 



CHAPTER III 



The true, pre-human relationship between the Palaearctic 

 and Nearctic faunas 



The so-called Amphiatlantic species 230 



Doubtful cases, p. 233 - "Westarctic" species, p. 237 - The American element 

 of the British flora, p. 240. 



The chance of spontaneous transatlantic dispersal at the present time 242 



The theories of earlier transatlantic land-connections 253 



The Iceland-Greenland bridge, p. 253 -Affinities in the south, p. 280 -Wege- 

 ner, pro and contra, p. 284. 



Circumpolar animals 286 



The fossil evidence 306 



Bibliography 313 



Conclusions 322 



Index 324 



73810 



