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, 7 aS 
A Ss =< es 
WEY WINTER: 
Fig. 108.—Seasonal changes of colour in Ptarmigan (Lagofus 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- 
