THE COLOURS OF ANIMALS AND PLANTS 131 



the black deepest of all. If the superficial ones con- 

 tract, the deeper ones will become more apparent, 

 and vice versa. These changes of colour always bear 

 a relation to the surface on which the animal is 

 placed at the time, and are therefore supposed with 

 good reason to be protective. 



Aggressive Resemblances. 



These aid the approach of their possessor to its 

 prey, through a superficial resemblance to its general 

 environment or to other objects. The Lion and Tiger 

 are good examples of general aggressive resem- 

 blances, the lion resembling in colour the desert in 

 which it lives, and the stripes on the tiger rendering 

 it easy to conceal itself among the long grass. So 

 with the Polar bear, which not only is of the same 

 colour as the snow, but also has a curious shapeless 

 outline when lying down, not unlike a heap of snow. 



Alluring Resemblances. 



These attract or entice the approach of prey. 

 Lophius piscatorius, the angler-fish, which conceals 

 itself in the mud at the bottom of the water, 

 is provided with long tentacles, which are mis- 

 taken by small fish for worms writhing in the 

 muddy water. The body of the angler, being 

 concealed in the mud, is not seen, and the prey, 

 deceived by what they imagine to be worms, are 

 themselves eaten by the angler-fish. Again, certain 

 deep-sea fish have a luminous phosphorescent organ 



