From the evidence which Darwin has collected, it appears to me impossible to doubt that an æsthetic sense is displayed by many birds, and not a few mammals. This of course does not necessarily imply that the _standards_ of such a sense are the same as our own; nor does it necessarily imply that there is any constant relation between such a sense and high levels of intelligence in other respects. In point of fact, such is certainly not the case, because the best evidence that we have of an æsthetic sense in animals is derived from birds, and not from mammals. The most cogent cases to quote in this connexion are those of the numerous species of birds which habitually adorn their nests with gaily coloured feathers, wool, cotton, or any other gaudy materials which they may find lying about the woods and fields. In many cases a marked preference is shown for particular objects--as, for instance, in the case of the Syrian nut-hatch, which chooses the iridescent wings of insects, or that of the great crested fly-catcher, which similarly chooses the cast-off skins of snakes. But no doubt the most remarkable of these cases is that of the baya-bird of Asia, which after having completed its bottle-shaped and chambered nest[47], studs it over with small lumps of clay, both inside and out, upon which the cock-bird sticks fire-flies, apparently for the sole purpose of securing a brilliantly decorative effect. Other birds, such as the hammer-head of Africa, adorn the surroundings of their nests (which are built upon the ground) with shells, bones, pieces of broken glass and earthenware, or any objects of a bright and conspicuous character which they may happen to find. The most consummate artists in this respect are, however, the bower-birds; for the species of this family construct elaborate play-houses in the form of arched tunnels, built of twigs upon the ground. Through and around such a tunnel they chase one another; and it is always observable that not only is the floor paved with a great collection of shells, bones, coloured stones, and any other brilliant objects which they are able to carry in their beaks, but also that the walls are decorated with the most gaudy articles which the birds can find. There is one genus, in Papua, which even goes so far as to provide the theatre with a surrounding garden. A level piece of ground is selected as a site for the building. The latter is about two feet high, and constructed round the growing stalk of a shrub, which therefore serves as a central pillar to which the frame-work of the roof is attached. Twigs are woven into this frame-work until the whole is rendered rain-proof. The tent thus erected is about nine feet in circumference at its base, and presents a large arch as an entrance. The central pillar is banked up with moss at its base, and a gallery is built round the interior of the edifice. This gallery is decorated with flowers, fruits, fungi, &c. These are also spread over the garden, which