148 DARWINISM AND THE PROBLEMS OF LIFE 



but this is a revenge that cannot bring the slain animal 

 back to life. 



In the case of many animals, such as the butterflies, 

 one bite is fatal, and hence those poisonous and ob- 

 noxious animals were always selected which were 

 calculated by their appearance to prevent enemies 

 from trying whether they were edible or not. It is 

 important, further, that all the marked animals should 

 have as nearly as possible the same indication. Then 

 carnivorous animals will not test the edibility of any 

 new offensive creature that crosses their path, but will 

 remember their experience of similar creatures and 

 leave it alone. Hence it is that so many poisonous 

 organisms have yellow colouring. There are even 

 edible animals with the colour because it affords 

 them protection ; the value of this adaptation, which 

 we will examine more closely in the sixth chapter, is 

 obvious. Possibly this is the explanation of the two 

 bright yellow spots at the back of the head of the 

 ringed adder, which have given occasion for the pretty 

 saying, that the snake, as the harmless creature is 

 popularly called, wears a crown. 



Natural selection has also given many amphibians 

 a protective colouring, instead of the disgusting and 

 warning colours. A toad closely resembles a clod of 

 earth, the brown frog is not easy to distinguish from 

 the soil, and the tree-frog can hardly be detected in the 

 green foliage. The latter can change its colour — not 

 voluntarily, but it assumes shades from brown to green 

 according to its disposition, the weather, and the 

 environment. 



