Returning to sexual colour, the dull summer female plumage which characterises so many ground-feeding birds is all the more remarkable as they are the mates of males for the most part distinguished by unusual brilliancy of plumage. The few exceptions to this rule are of the most interesting nature, and go eminently to prove it. In these exceptions it happens that the female birds are more brightly plumaged than the males. But the remarkable trait comes out that in nearly the whole of these cases the male sits upon the eggs. Now this fact more than any other would seem to indicate that the protection afforded by obscure colouring is directly intended to secure the bird's safety during the long and most critical period of its life. This law of protective colouring, it will be seen, most influences those species which build on the ground, and one or two examples may be adduced from our own avi-fauna, as in the case of the rare dotterel, which breeds on the fells. In winter the colouring of the sexes in this species is almost identical; but when the breeding season comes round, the female dons a well-defined and comparatively conspicuous plumage, while it is found that the dull-coloured male alone sits upon the eggs. Mr. Wallace has pointed that the bee-eaters, mot-mots, and toucans--among the most brilliant of tropical or semi-tropical birds--all build in holes in trees. In each of these cases there is hardly any difference in the plumage of the sexes, and where this is so the above rule is almost invariable. Again, our native kingfisher affords an illustration. Woodpeckers, many of which are brightly coloured above, build in the boles of trees, and our own titmice, with their exquisite tints, construct domed nests. Visitors to the Zoological Gardens in Regent's Park will have noticed that the orange-plumaged orioles have pensile nests, which is a characteristic of the order to which they belong, most of the members of which are conspicuous. Bird enemies come from above rather than below, and it will be noticed that the modifications referred to all have reference to the upper plumage. Protective colouring, having for its object the preservation of the species which adopt it, will be found to enter more or less into the economy of every animal and bird and insect in a state of nature; and therefore it will be seen that there is a general harmony between the colours of an animal and those of its habitation, of which fact almost every living natural object furnishes evidence.