pons, are
probably more numerous than have been hitherto supposed; and, if so, we
shall be able to explain a considerable amount of colour in nature for
which no use has hitherto been conjectured. The brilliant and varied
colours of sea-anemones and of many coral animals will probably come
under this head, since we know that many of them possess the power of
ejecting stinging threads from various parts of their bodies which
render them quite uneatable to most animals. Mr. Gosse describes how, on
putting an Anthea into a tank containing a half-grown bullhead (Cottus
bubalis) which had not been fed for some time, the fish opened his mouth
and sucked in the morsel, but instantly shot it out again. He then
seized it a second time, and after rolling it about in his mouth for a
moment shot it out again, and then darted away to hide himself in a
hole. Some tropical fishes, however, of the genera Tetrodon,
Pseudoscarus, Astracion, and a few others, seem 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 combination
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 th