ANIMALS THAT CHANGE COLOUR 73 
arise from coloured oils that reside in cavities 
situated beneath the skin, and change their 
position according to the mental state of the 
fish, or under the influence of its surroundings. 
The octopus is another creature that has 
the power to alter its colour. Darwin states : 
“ They appear to vary their tints according 
to the nature of the ground over which they 
pass ; when in deep water, their general shade 
was purplish-brown, but when placed on the 
land, or in shallow water, the tint changed 
into one of greenish-yellow. The colour, 
examined more carefully, was a French grey, 
with numerous minute spots of bright yellow; 
the former varied in intensity, the latter 
entirely disappeared and appeared again by 
turns. These changes were effected in such 
a manner that clouds, varying in tint between 
a hyacinth-red and a chestnut-brown, were 
continually passing over the body.” 
Among the Crustacea we have an example 
in the common prawn that is able to alter its 
colour from a dark to a light tint so as to 
render itself as inconspicuous as possible amidst 
its surroundings. iEsop’s prawn (Hippolyte 
varians), however, is far more remarkable, 
for not only does it assume various colours 
such as green, red and brown, in order to 
harmonize with its habitat, but it indulges 
