is nothing more than it pretends to be — a guess. 

 I vouch for nothing beyond its probability. In- 

 deed, I might add, while on this subject, that 

 the naturalist experiences few greater difficulties 

 than in assembling data as to the natural span of 

 the wild lives he studies. If anything can be more 

 difficult, it is to determine why some animals live 

 longer than others. Rarely does a feral creature die 

 of old age. Disease, adverse weather, lack of food, 

 and enemies all combine to cut short the existence 

 of nearly all individual forms of life. But aside 

 from these factors, there is a natural disparity in 

 the longevity of animals; a disparity so wide- 

 spread and patent that it is a matter of common 

 observation. Yet, why is it, for example, that the 

 tiger, the lion, or even the hippopotamus, will die 

 of old age long before the elephant will reach its 

 prime? It is said that an elephant will live to be 

 two hundred years old. A tiger is old at twenty 

 years, a lion will live for twenty-five years, and a 

 hippopotamus reaches the age of forty. Then again, 

 a crow or a swan can survive for a hundred years 

 or more while an eider duck or parrot might live 

 twice this long. The fresh-water carp and the pike, 

 and the tortoise, too, have been known to pass the 



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