VIII 
ORIGIN AND USES OF COLOUR IN ANIMALS 
195 
whites and yellows, and the Satyridae or ringlets—we shall find 
no great disproportion in colour between those of temperate 
and tropical regions. 
The various facts which 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 colour 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 produce 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 excejffiional 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 undereoina: 
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, which, 
