THE PASSENGER PIGEON IN PENNSYLVANIA 167 



ated and immutable, are constantly subject to change, 

 through a process of adaptation, by which those best 

 fitted to survive in changing environments, become the 

 prevailing species, at the expense of other species andi 

 varieties — This process of natural selection being so 

 potent and universal that it seems capable, with otheil 

 less important causes, of explaining how all of the ex- 

 isting species have decended from one or a very few< 

 low forms of life — has excited a controversy which 

 seems incapable of being laid to rest; but Darwin's 

 theory has been embraced by many of the ablest natu^ 

 ralists. It has induced great changes in the methods 

 cf biology and kindred sciences. His death occurred! 

 April 20, 1882.— John C. French. 



