Some eight years ago a distinguished American painter, Mr. Abbott Thayer, was able to add very importantly to our knowledge of the ways in which colour serves to conceal animals when in their natural surroundings. Mr. Thayer was able to do this owing to the fact that he was a devoted student of woodland life. This, however, alone was not enough. Mr. Thayer had the special ability to deal with this subject which comes from the trained eye of an artist. He had, above all, the knowledge of “tone values” and of the illusive and delusive effects of false shading and of colour-spots and bars, and of complementary colours and “irradiation”—which only a painter who deals every day in the most practical way with these matters can attain to. Mr. Thayer showed eight years ago—and demonstrated conclusively by means of models, one of which he presented to the Natural History Museum at my request—that in very many cases it is of no use for an animal to be of the same colour as its surroundings, since if the animal (a bird, or a quadruped, or a fish) is of plump and rounded shape and is observed under the open canopy of heaven, a deep shadow will exist on its lower surface and make it as obvious as a shaded charcoal drawing on a piece of light-brown paper. But if the back of the animal is of a dark tint and its belly white or whitish, then the effect of light and shade is (Mr. Thayer showed) completely counteracted and the animal becomes totally invisible in its natural surroundings. Mr. Thayer’s model demonstrating this consists of two life-size wooden models of ducks seated on a stick—one to the left, the other to the right. The stick, with the two models on it, is fixed horizontally in a box, which is open above (that is, has no lid) and is also open in front. The box is, in fact, a little stage, lit from above by the light of the sky, and its three remaining sides are sufficiently high to form a complete background to the model ducks, whose perch runs across the “scene” at some 7 in. or 8 in. from the floor of the box. The box itself is lined with a pale purplish-brown flannel, and each bird is tightly covered with the same material. When so prepared the box is placed on a table under a skylight (where it is to stay), the table being high enough to bring the ducks just below the line of sight. Of course, deep shadows are formed by the top-light on the under side of the beak, head, and body of the models, and in spite of their colour being itself identical with that of the walls of the box, they are as obvious as it is possible for anything to be. Now Mr. Thayer takes his paints and very carefully darkens the back of one of the ducks and whitens its belly and the under side of its head and beak. The light and dark regions merge into one another along the side of the bird by skilful gradation. When this shading and whitening is finished (and, of course, the perfection of the result depends on the continuance of the right amount of