There arrive every year in this country, from the north, flocks of pretty little birds called snow-buntings. They come from within the Arctic Circle, and are so variable in their plumage that naturalists almost despaired of ever getting a characteristic description. Indeed, so much a puzzle did these little strangers offer, that for long they were described by the older naturalists as three different birds. Of course, we now know that the mountain, tawny, and snow bunting are one; and this because they have been obtained in almost every possible stage of transition. They breed upon the summits of the highest hills with the ptarmigan; and like that bird regulate their plumage according to the prevailing aspect of their haunts. In this they succeed admirably, and flourish accordingly. VI. ADAPTATION TO HAUNT. The process of natural selection, tending to the survival of the fittest, would almost invariably seem to use colour as its main working factor. The exemplification of this law is, perhaps, nowhere better seen than in the colouring of animals and birds. In the keen struggle for existence, the creature which conforms most nearly to its environment is the one most likely to survive, and therefore perpetuate its characteristics. For upon the fact that the peculiarities of the parents are reproduced in their offspring depends the whole theory of evolution. This may at first suggest that the generality of animals and birds closely conform to the type of the parent stock, and that therefore there is little chance of variation. But while this is so, it is equally true that when any "sport" occurs this is tenaciously retained providing it possesses any advantages over its neighbours in the struggle for existence. In this way a new type may be set up, differing so far from the original as in time to rank as a species.