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46 NATURAL SELECTION inthis point Mr. A. Sidgwick, in a paper read before the RugbySchool Natural History Society, gives the following original"observation : I myself have more than once mistaken Cilixcompressa, a little white and gray moth, for a piece of bird'sdung dropped upon a leaf, and vice versd the dung for the moth.Bryophila Glandifera and Perla are the very image of themortar walls on which they rest ;and only this summer, inSwitzerland, I amused myself for some time in watching amoth, probably Larentia tripunctaria, fluttering about quiteclose to me, and then alighting on a wall of the stone of thedistrict which it so exactly matched as to be quite invisible acouple of yards off." There are probably hosts of these resemblanceswhich have not been observed, owing to the difficultyof finding many of the species in their stations of naturalrepose. Caterpillars are also similarly protected. Manyexactly resemble in tint the leaves they feed upon others;arelike little brown twigs, and many are so strangely marked orhumped, that when motionless they can hardly be taken to beliving creatures at all. Mr. Andrew Murray has remarkedhow closely the larva of the peacock moth (Saturnia pavoniaminor)harmonises in its ground colour with that of the youngbuds of heather on which it feeds, and that the pink spotswith which it is decorated correspond with the flowers andflower-buds of the same plant.The whole order of Orthoptera, grasshoppers, locusts,crickets, etc., are protected by their colours harmonising withthat of the vegetation or the soil on which they live, and inno other group have we such striking examples of specialresemblance. Most of the tropical Mantidae and Locustidseare of the exact tint of the leaves on which they habituallyrepose, and many of them in addition have the veinings oftheir wings modified so as exactly to imitate that of a leaf.This is carried to the furthest possible extent in the wonderfulgenus, PhyIlium, the " walking leaf," in which not onlyare the wings perfect imitations of leaves in every detail, butthe thorax and legs are flat, dilated, and leaf-like ;so thatwhen the living insect is resting among the foliage on whichit feeds, the closest observation is often unable to distinguishbetween the animal and the vegetable.The whole family of the Phasmidae, or spectres, to which