382 THE INFLUENCE OF LIVING SURROUNDINGS. 



which it suggests, but which can only be solved by experiment. 

 I shall here discuss another important instance of the same kind 

 which is very much to the point the Means of Protection, 

 namely, bestowed by nature on both pursuers and pursued to 

 enable them to attain their end, that is to say to capture their 

 prey on the one hand, or to escape capture on the other. 



Protection by imitation of surrounding objects. It is well 

 known that a great number of living animals are enabled to 

 escape their pursuers by their more or less strong resemblance 

 in form and colour to the objects among which they live, in 

 which case the resemblance is protective ; while others, on the 

 contrary, are specially qualified by the same circumstance to 

 pursue their prey with success. Thus a crowd of new agents of 

 selection among forms are added to those already discussed in 

 the former chapters. For it is self-evident that every alteration 

 that takes place in the co-ordination of the conditions which 

 surround any given species of animal must deprive it of the pro- 

 tection it derives from its resemblance to a particular plant, let 

 us say, if that very plant is exterminated ; and in the same way 

 that an accident of colouring, which has hitherto occasioned no 

 special resemblance to any object, may suddenly become a 

 powerful instrument in facilitating attack or self-defence. Thus 

 a selection will be effected between different forms which had 

 previously been equally protected. 125 



It is, of course, impossible to investigate in this place the 

 greater number of the known cases of such protective resem- 

 blance, and it will suffice to discuss a few of the most instructive 

 examples. I shall here adopt the arbitrary division of these 

 cases into two classes, which has become general : into those, 

 namely, of the resemblance of animals to inanimate objects as 

 stones, sand, the soil, and living plants and those of resem- 

 blance to other living animals ; but merely for convenience sake, 

 since I can find no principle on which such an artificial division 

 can be based. 



It has long been a well-established fact that very many 

 animals are effectually protected against their enemies by their 

 resemblance to stones or sand, lichens, leaves and twigs j and 

 every one who has at any time been engaged in collecting 



