266 DARWINISM chap. 



to have acquired the power of feeding on corals and medusae ; 

 and the beautiful bands and spots and bright colours with 

 which they arc frequently adorned, may be either protective 

 wlicn feeding in the submarine coral groves, or may, in some 

 cases, be warning colours to show that they themselves are 

 l)oisonous and uneatable, 



A remarkable illustration of the wide extension of warning 

 colours, and their very definite purpose in nature, is afforded 

 by what may now be termed " Mr. Belt's frog." Frogs in all 

 parts of the world are, usually, protectively coloured with 

 greens or browns ; and the little tree-frogs are either green 

 like the leaves they rest upon, or curiously mottled to imitate 

 bark or dead leaves. But there are a certain number of very 

 gaily coloured frogs, and these do not conceal themselves as 

 frogs usually do. Such was the small toad found by Darwin 

 at Bahia Blanca, which was intense black and bright vermilion, 

 and crawled about in the sunshine over dry sand-hills and 

 arid plains. And in Nicaragua, Mr. Belt found a little frog 

 gorgeously dressed in a livery of red and blue, which did 

 not attempt concealment and was very abundant, a combina- 

 tion of characters Avhich convinced him that it was uneatable. 

 He, therefore, took a few specimens home with him and 

 gave them to his fowls and ducks, but none would touch 

 them. At last, by throwing down pieces of meat, for 

 which there was a great competition among the poultry, 

 he managed to entice a young duck into snatching up 

 one of the little frogs. Instead of swallowing it, however, 

 the duck instantly threw it out of its mouth, and went 

 about jerking its head as if trying to get rid of some un- 

 pleasant taste. ^ 



The power of predicting what will happen in a given case 

 is always considered to be a crucial test of a true theory, 

 and if so, the theory of warning colours, and with it that of 

 mimicry, must be held to be well established. Among the 

 creatures Avhich probably have warning colours as a sign of 

 ine(li])ility are, the l)rilliantly coloured nudibranchiate molluscs, 

 those curious annelids the Nereis and the Ajihrodite or sea- 

 mouse, and many other marine animals. The brilliant colours 

 of the scallops (Pecten)and some other bivalve shells are perhaps 

 ^ The Naturalist in Nicaragua^ p. 321. 



