164 THE COLOUES OF ANIMALS 



for purposes of defence or for killing prey, the snake 

 would be comparatively harmless. Hence it .would 

 be to the advantage of certain snakes to advertise 

 publicly the fact that they are dangerous, retaining 

 the poison to use if necessary ; and others would gain 

 by concealing themselves by Protective Eesemblance, 

 while they also would use their poison fangs if detected 

 and attacked. The question is not whether one of 

 these methods is better than the other, but whether 

 either of them is better than an intermediate con- 

 dition ; so that we can well understand why one 

 group of poisonous snakes should adopt one method, 

 while the other method is made use of by another 

 group. 



Warning Colours in Amphibia 



Among the Amphibia a beautiful example has been 

 afforded by Mr. Belt's acute powers of observation. 1 

 ' In the woods around Santo Domingo there are many 

 frogs. Some are green or brown, and imitate green 

 or dead leaves, and live amongst foliage. Others are 

 dull earth-coloured, and hide in holes and under logs. 

 All these come out only at night to feed, and they are 

 all preyed upon by snakes and birds. In contrast 

 with these obscurely coloured species another little" 

 frog hops about in the daytime, dressed in a bright 

 livery of red and blue. He cannot be mistaken for 

 any other, and his flaming vest and blue stockings 



' Loc. tit. p. 32L 



