186 



Biology in America 



is the last representative of a once thriving family, which at 

 one time had a much wider distribution than at present. The 

 sewellel is an animal somewhat resembling a large rat, which 

 digs his home among the roots of the forest trees and stores 

 therein the harvest which he gathers from its herbs. 



Several million years ago, more or less, there lived in North 

 America a numerous race of animals related to the opossum 

 and kangaroo, the marsupials, to which reference has been 

 made in the preceding chapter. Then they disappeared from 

 what is now the United States, for what reason we do not 



MOUNTAIN BEAVER, OR SEWELLEL 

 Courtesy of the U. 8. Bureau of Biological Survey. 



know a mysterious disappearance of the past, . which the 

 palaeontological sleuth may never solve. The most likely ex- 

 planation is that they were driven south by the wolves and 

 tigers and others of their ilk, the robber barons of the ani- 

 mal world. More recently one of their number, the opossum, 

 has once more ventured northward as far as the northern 

 United States (Michigan and New York). 



Have all these facts laboriously gathered by many men 

 in many years any practical value? Even had they none 

 they would still be well worth while because of the light which 

 they, in conjunction with the "hard facts" of palaeontology, 



