34 DISTRIBUTION OF ANIMALS. [PART I: 
mistaken for something else. Then again, insects have enemies 
in every stage of their existence—the egg, the larva, the pupa, 
and the perfect form; and the abundance of any one of these 
enemies may render their survival impossible in a country other- 
wise well suited to them. Ever bearing in mind these two 
opposing classes of facts, we shall not be surprised at the 
enormous range of some groups of insects, and at the extreme 
localization of others; and shall be able to give a rational account 
of many phenomena of distribution that would otherwise seem 
quite unintelligible. 
