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 are frequently adorned, may be either protective 
when feeding in the submarine coral groves, or may, in some 
cases, be warning colours to show that they themselves are 
poisonous 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 which 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 ont of its mouth, and went 
about jerking its head as if trying to get rid of some un¬ 
pleasant taste. 1 
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 which probably have warning colours as a sign of 
inedibility are, the brilliantly coloured nudibranchiate molluscs, 
those curious annelids the Nereis and the Aphrodite or sea- 
mouse, and many other marine animals. The brilliant colours 
of the scallops (Pecten)and some other bivalve shells are perhaps 
1 The Naturalist in Nicaragua, p. 321. 
