CHAPTER XXII 



Adaptation to environment in animals Deep sea animals The colouration 

 of animals Protective and aggressive resemblances Warning colours 

 Mimicry Epiganiic ornamentation . 



IN the last few chapters we have discussed a number of facts 

 selected from that great and ever increasing mass of evidence 

 which leads us to the inevitable conclusion that the present con- 

 dition of the fauna and flora of the earth, with their almost 

 endless diversity of plants and animals, is the outcome of a long 

 process of organic evolution. It is desirable at this stage of our 

 inquiry to emphasize the fact that this evolution, in the main, 

 has been of a progressive character, and of such a character, 

 moreover, as to maintain a more or less perfect harmony between 

 the organism and its environment. 



Adaptation in bodily organization and in corresponding 

 function, whereby each kind of plant or animal is enabled to 

 meet the constant demands made upon it and maintain its 

 existence in the endless warfare of life, is the great outstanding 

 feature of living things. So universal is this adaptation that 

 we are apt to take it for granted, and any want of it is at once 

 recognized as an exception and an anomaly. Anyone, for 

 example, who watches the slow and clumsy movements of a 

 tortoise cannot fail to be struck with the fact that the limbs of 

 this animal are but ill-suited for purposes of locomotion, but 

 even in this case there is compensation in that the tortoise 

 carries its place of refuge about with it and has therefore little 

 need to hurry itself. 



We have seen in an earlier chapter how completely the 

 pentadactyl limbs of air-breathing vertebrates may become 

 modified from their primitive condition in correspondence with 

 changes in the mode of life. The fore limbs, adapted in the 

 first instance for locomotion on land, have become changed in 

 the whales, seals and dugongs into paddles ; in the pterodactyls, 

 birds and bats into wings, and in man into organs of prehension. 



