Amongst caterpillars there are many cases of remarkable resemblances in color between the animal and its surroundings. The green color of many of those forms that remain on the leaves of the food-plant during the day will give, even to the most casual observer, the impression that the color is for the purpose of concealment; and that it does serve to conceal the animal there can be no doubt. But even from the point of view of those who maintain that this color has been acquired because of its protective value it must be admitted that the color is insufficient, because some of these same green caterpillars are marvellously armed with an array of spines which are also supposed to be a protection against enemies. Equally well protected are the brown and mottled geometrid caterpillars. These have, moreover, the striking and unusual habit of fixing themselves by the posterior pairs of false legs, and standing still and rigid in an oblique position on the twigs to which they are affixed. So close is their resemblance to a short twig, that even when their exact position is known it is very difficult to distinguish them. Grasshoppers that alight on the ground are, in many cases, so similar to the surface of the ground that unless their exact location is known they easily escape attention, while the green color of the katydid, a member of the same group of orthoptera, protects it from view in the green foliage of the trees where it lives. The veinlike wings certainly suggest a resemblance to a leaf, but whether there is any necessity for so close an imitation may be questioned. There can be little doubt in some of these cases that the color of the animal may be a protection to it, but as has been hinted already, it is another question whether it acquired these colors because of their usefulness. Nevertheless, if the color is useful to its possessor, it is an adaptation in our sense of the word, without regard to the way in which it has been acquired. Even, for instance, if the resemblance were purely the outcome of chance in the sense that the color appeared without relation to the surroundings, it would still be an adaptation if it were of use to the animal under the ordinary conditions of life. In the lower groups numerous cases in which animals resemble their surroundings could be given. Such cases are known in crustacea, worms, mollusks, hydroids, etc., and the possible value of these resemblances may be admitted in many instances.