contrary, an important means of protection. The Crabs in question escape pursuit in consequence of this disguise, and it is to be observed that each species chooses the very material which makes it most unrecognizable to plant upon the exterior of its body; those species which live chiefly in regions where Cystosiras are indigenous deck themselves in Cystosiras, whilst those which inhabit the same places as Ulvæ carry Ulvæ on their backs.[1] This also serves as aggressive mimicry; for, as Mr. Woodward writes, "thus disguised like Indians stalking game, they can readily approach their more active prey."[2] Mr. Bateson observed this active mimicry at Plymouth, and describes how a Crab seizes a piece of weed, tears off a fragment, chews the end in its mouth, and then rubs it firmly on its head and legs until it is caught by the curved hairs and fixed. "The whole proceeding is most human and purposeful. Many substances, as Hydroids, Sponges, Polyzoa, and weeds of many kinds and colours, are thus used; but these various substances are nearly always symmetrically placed in corresponding parts of the body, and particularly long plume-like pieces are fixed on the head."[3] Dr. Willey records a similar observation which he made on the faces of rocks near Tjibodas (Java). "I found a quantity of small caterpillars living on the powdery Alga which makes greenish-white patches on the rocks. The caterpillars had so completely covered themselves with the Alga as to be only discernible by their movements on close inspection, and their disguise must effectually protect them from foes."[4] "Equally marvellous, too, is the case of many kinds of caterpillars which spin their cocoons on the bark of trees, and cover the structures wherein they are subsequently to undergo transformation into the chrysalis state with lichens and fragments of bark, that their temporary resting place may not be noticed by insectivorous birds."[5] When the caterpillar of the Indian butterfly, Limenitis procris, "comes out of the egg, it betakes itself at once to the very point of a tender leaf, and eats down steadily on both sides of the midrib, which
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