Let us see how the adoption of protective colouring holds as applied to these species--all of which are brown in summer, white in winter. The Iceland falcon and the ptarmigan have pretty much the same habitat, the one preying upon the other. The ptarmigan's plumage during the breeding season is dark brown, even approaching to black; but in autumn, during the transition stage, it is grey, this being the general tint of the mosses and lichens among which it lives. Suppose, however, that the summer bird never changed its plumage, what chance of survival would it stand against its enemies when the ground was covered with snow? Remaining, as it would, a black speck on the otherwise white surface, it would in a few years become extinct. The ptarmigan, then, furnishes an example of the assumption of three different states of plumage, each assimilating to the physical conditions by which it is surrounded. Of course the same rule applies to the falcon, which is also white. Precisely the same set of facts operate in the case of the large snowy owl in the fir countries which it inhabits. Here its food consists of lemmings, Alpine hares, and birds, particularly the willow-grouse and ptarmigan. The balance of nature would be slightly against it, however, in the capture of animals which have assumed protective colouring, and hence we are told that "it has been known to watch the grouse-shooters a whole day for the purpose of sharing the spoil. On such occasions it perches on a high tree, and when a bird is shot skims down and carries it off before the sportsman can get near it." Yet again the same reasoning applies to the beautiful silver fox, which structurally in nowise differs from its red-furred cousin of more southern counties.