334 SCOTT'S LAST EXPEDITION 



part of the Benthos to originate in the Northern Hemisphere and 

 migrate southward. 



The work of Wallace on the distribution of land animals has 

 shown that there appears to have been a tendency throughout 

 the history of the earth for the land animals to originate in the 

 Northern Hemisphere and gradually find their way south. The 

 great belt of land which through long ages has almost encircled 

 the northern half of the world seems to have been nature's work- 

 shop for the evolution of types. These new forms spreading out 

 from their points of origin had to find their way southward along 

 the attenuated land areas of South America, Africa, and Austral- 

 asia. Thus on account of their relative isolation these three 

 southern continents b.ecame characterised by peculiar and in some 

 cases comparatively primitive assemblages of animals. They 

 became, as it were, behind the fashion. For instance, Australia 

 to-day still has its marsupial population of kangaroos and such- 

 like animals. In Europe marsupial types are only found as fos- 

 sils, showing that they lived here millions of years ago in the 

 mesozoic ages of the earth's history, but have long since been ex- 

 terminated and supplanted by newer types. 



On account of the inadequate nature of the fauna of large 

 parts of the Southern Hemisphere, man has had to stock these 

 lands with northern animals. 



Very few cases are known where land animals of a southern 

 origin have advanced northwards. Whether this generalisation 

 applies in the case of the marine benthos of the continental 

 shelves presents an interesting field of enquiry. The collections 

 brought home in recent years by the various Antarctic and other 

 expeditions which have trawled in the Southern Hemisphere will, 

 perhaps, make it possible to give some sort of answer to this 

 question. 



