Evidences of Theory of Natural Selection. 317 



Protective Colouring. 



A vast number of animals are rendered more or less 

 inconspicuous by resembling the colours of the surfaces 

 on which they habitually rest. Such, for example, 

 are grouse, partridges, rabbits. &c. Moreover, there 



Autumn 



■\.^ 



SUMMER. ■ 



Fig. 108.— Seasonal changes of colour in Ptarmigan {Lagopus mutus). 

 Drawn from stuffed specimens in the British Museum, \ nat. size, 

 with appropriate surroundings supplied. 



are many cases in which, if the needs of the creature 

 be such that it must habitually frequent surfaces of 

 different colours, it has acquired the power of changing 

 its colour accordingly — e. g. cuttle-fish, flat-fish, 

 frogs, chameleons, &c. The physiological mechanism 

 whereby these adaptive changes of colour are pro- 



