

The Struggle for Existence 139 



in the middle "of a little patch of lichen, where its self-efface- 

 ment is complete. Perhaps it is more comfortable as well as safer 

 to rest in surroundings the general colour of which is like that of 

 the animal's body. (3) The fishes that live among the coral-reefs 

 are startling in their brilliant coloration, and there are many 

 different patterns. To explain this it has been suggested that 

 these fishes are so safe among the mazy passages and endless 

 nooks of the reefs, that they can well afford to wear any colour 

 that suits their constitution. In some cases this may be true, but 

 naturalists who have put on a diving suit and walked about among 

 the coral have told us that each kind of fish is particularly suited 

 to some particular place, and that some are suited for midday 

 work and others for evening work. Sometimes there is a sort of 

 Box and Cox arrangement by which two different fishes utilise 

 the same corner at different times. 



2 



Gradual Change of Colour 



The common shore-crab shows many different colours and 

 mottlings, especially when it is young. It may be green or grey, 

 red or brown, and so forth, and it is often in admirable adjustment 

 co the colour of the rock-pool where it is living. Experiments, 

 which require extension, have shown that when the crab has 

 moulted, which it has to do very often when it is young, the colour 

 of the new shell tends to harmonise with the general colour of the 

 rocks and seaweed. How this is brought about, we do not know. 

 The colour does not seem to change till the next moult, and not 

 then unless there is some reason for it. A full-grown shore-crab 

 is well able to look after itself, and it is of interest to notice, there- 

 fore, that the variety of coloration is mainly among the small indi- 

 viduals, who have, of course, a much less secure position. It is 

 possible, moreover, that the resemblance to the surroundings 

 admits of more successful hunting, enabling the small crab to take 

 its victim unawares. 



