VIII ORIGIN AND USES OF COLOUR IN ANIMALS 195 



Avhites and yellows, and the Satyridre or ringlets — we shall find 

 no great disj^roportion in colour between those of temperate 

 and tropical regions. 



The various facts Avhich have now briefly been noticed are 

 sufficient to indicate that the light and heat of the sun are 

 not the direct causes of the colours of animals, although they 

 may favour the production of coloiu' when, as in tropical 

 regions, the persistent high temperature favours the develop- 

 ment of the maximum of life. We will now consider the 

 next suggestion, that light reflected from surrounding coloured 

 objects tends to j^roduce corresponding colours in the animal 

 world. 



This theory is founded on a number of very curious facts 

 which prove, that such a change does sometimes occur and is 

 directly dependent on the colours of surrounding objects ; but 

 these facts are comparatively rare and exceptional in their 

 nature, and the same theory will certainly not apply to the in- 

 finitely varied colours of the higher animals, many of which 

 are exposed to a constantly varying amount of light and 

 colour during their active existence. A brief sketch of these 

 dependent changes of colour may, however, be advantageously 

 given here. 



Variable Protective Colouring. 



There are two distinct kinds of change of colour in animals 

 due to the colouring of the environment. In one case the 

 change is caused by reflex action set up by the animal seeing 

 the colour to be imitated, and the change produced can be 

 altered or repeated as the animal changes its position. In the 

 other case the change occurs but once, and is probably not 

 due to any conscious or sense action, but to some direct in- 

 fluence on the surface tissues while the creature is undergoing 

 a moult or change to the pupa form. 



The most striking example of the first class is that of the 

 chameleon, which changes to white, brown, yellowish, or 

 green, according to the colour of the object on which it rests. 

 This change is brought about by means of two layers of 

 pigment cells, deeply seated in the skin, and of bluish and 

 yellowish colours. By suitable muscles these cells can be 

 forced upwards so as to modify the colour of the skin, M-hich, 



