Page:Darwinism by Alfred Wallace 1889.djvu/231

Rh Professor E. S. Morse of Salem, Mass., found that most of the New England marine mollusca were protectively coloured; instancing among others a little red chiton on rocks clothed with red calcareous algæ, and Crepidula plana, living within the apertures of the shells of larger species of Gasteropods and of a pure white colour corresponding to its habitat, while allied species living on seaweed or on the outside of dark shells were dark brown. A still more interesting case has been recorded by Mr. George Brady. 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."

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.

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 Sphingidæ, the forepart of the body