ENVIRONMENT, PAST AND PRESENT 51 



as far as they seem to be known, are wanderings 

 which keep them in touch with a changing food 

 supply that on the whole tends to vary with the 

 rains. Referring to these as they are seen in Aus- 

 tralia, Wetmore says (p. 33) "Though this seems 

 mere vagrancy, it is migration of a kind." And so 

 indeed it is but we know all too little about it. In 

 certain cases it may be true migration (p. 105). It 

 is on the border-line and it is with some reluctance 

 that one must exclude it by definition. But if a 

 discussion of migration is to serve a useful purpose, 

 it is imperative that a clear understanding of the 

 scope of the term be determined at the outset. 



In no other part of the world has the custom of 

 migration been as extensively developed as in the 

 high latitudes of the northern hemisphere. A gen- 

 eral explanation of the situation is self-evident when 

 one scans the map of the world, particularly if one 

 takes a few liberties with it as we have done in 

 Fig. 8. The land masses of the southern hemi- 

 sphere have been superimposed, in their correspond- 

 ing latitudes, on those of the northern. They ap- 

 pear inverted and if the map is looked at upside 

 down the significance of the arrangement will be 

 better appreciated. Placed thus, the southernmost 

 tip of Australia is level with New York, while New 

 Zealand fails entirely to reach even the western 



