The change from green to brown and from brown to green in certain tree frogs and in the lizard (_Anolis_), which is popularly supposed to take place according to whether the background is green or brown, is not after all, it appears, connected with the color of the background, but depends on certain other responses of the animals that have not yet been satisfactorily made out. If it be claimed that in summer the animal would generally be warm, and therefore, often green, and that this color would protect it at this time of year when the surroundings are green, and in winter brown, when this color is the prevailing one in temperate regions, then it might appear that the change is of use to the animal; but if it is true that the same change takes place in some of the lizards that live in the tropics, where the prevailing color is always green, it would appear that the result may have no direct relation with the surroundings. It has been shown in a number of well-authenticated cases that the pupæ of certain butterflies vary in color within certain limits in response to the color of the background. When the caterpillar fixes itself to some surface, and there throws off the outer skin, and acquires a new one, the color of the latter is influenced by the background. The result is a better protection to the pupa. The change is not brought about through the ocelli or eyes, but through the general surface of the skin, for the same change takes place when the eyes have been previously covered with a dark pigment. The growth of plants toward the light may be looked upon as an adaptive process, since only in the light can they find the conditions necessary for their life. The extraordinary elongation of shoots and young plants when grown in the dark may also be considered an adaptation for finding the light, since in this way a plant, deeply embedded in the ground, may ultimately reach the surface. Thus while the actual process of elongation in the dark is not in itself of any use, yet under the ordinary conditions of its life, this response may be of great benefit to the plant. The closing together of the leaves of some plants has been supposed to protect them from too rapid radiation of heat, and incidentally this purpose may be fulfilled; but since some tropical plants also close their leaves during the night, it can hardly be maintained that the closing has been acquired for this purpose. It has been suggested that the opening of certain flowers under certain conditions of light is connected with the visits of insects that bring about cross-fertilization.