On Mr Wallace's Theory of Birds' Nests 287 



of climate establish the same conditions of existence as regards 

 birds whose bodies are so small as to need great economy of their 

 little store of animal heat. As to the physical cause of this need 

 being met, there is no other explanation possible than this — that 

 the Creator has implanted in every creature those instinctive 

 desires and powers which are necessary for the preservation of its 

 existence. And this, too, is the explanation, and the only explana- 

 tion, of the adaptive or assimilated colouring, which, not being 

 dependent on any instinct or desire of the bird itself, can only be 

 the result of Mind directing the forces of Nature in a preconceived 

 and j)reordained direction. 



