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 became 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. 
