He says: "Amongst the Nullipore which matted together the laminaria roots in the Firth of Clyde were living numerous small starfishes (Ophiocoma bellis) which, except when their writhing movements betrayed them, were quite undistinguishable from the calcareous branches of the alga; their rigid angularly twisted rays had all the appearance of the coralline, and exactly assimilated to its dark purple colour, so that though I held in my hand a root in which were half a dozen of the starfishes, I was really unable to detect them until revealed by their movements."[78] These few examples are sufficient to show that the principle of protective coloration extends to the ocean as well as over the earth; and if we consider how completely ignorant we are of the habits and surroundings of most marine animals, it may well happen that many of the colours of tropical fishes, which seem to us so strange and so conspicuous, are really protective, owing to the number of equally strange and brilliant forms of corals, sea-anemones, sponges, and seaweeds among which they live.
_Protection by Terrifying Enemies._ A considerable number of quite defenceless insects obtain protection from some of their enemies by having acquired a resemblance to dangerous animals, or by some threatening or unusual appearance.

This is obtained either by a modification of shape, of habits, of colour, or of all combined.

The simplest form of this protection is the aggressive attitude of the caterpillars of the Sphingidae, the forepart of the body being erected so as to produce a rude resemblance to the figure of a sphinx, hence the name of the family.

The protection is carried further by those species which retract the first three segments and have large ocelli on each side of the fourth segment, thus giving to the caterpillar, when the forepart of its body is elevated, the appearance of a snake in a threatening attitude.
The blood-red forked tentacle, thrown out of the neck of the larvae of the genus Papilio when alarmed, is, no doubt, a protection against the attacks of ichneumons, and may, perhaps, also frighten small birds; and the habit of turning up the tail possessed by the harmless rove-beetles (Staphylinidae), giving the idea that they can sting, has, probably, a similar use.

Even an unusual angular form, like a crooked twig or inorganic substance, may be protective; as Mr.Poulton thinks is the case with the curious caterpillar of Notodonta ziczac, which, by means of a few slight protuberances on its body, is able to assume an angular and very unorganic-looking appearance.