The great power of variability in animals and plants is probably not yet fully comprehended. We know, however, from Darwin's experiments how many distinct varieties in the case of pigeons have been produced from the wild blue rock, each showing profound modification, not in colour alone, but also in bone structure. Then there are those which show the development of hoods and frills, and others, again, which have within them the homing instinct to an almost incredible degree. All this, of course, has been brought about by man, mostly by selection, and it serves to show how pliable nature is. What has been done to pigeons applies to domestic animals. Given a few years, any monstrosity can be produced, however extravagant; our shorthorns and blood horses have been produced out of the very sorriest material, and now stand as the idealised types of their kind. And what man does artificially, nature is doing daily, but by slow and sure methods of her own. None but those who have dipped beneath the surface can conceive of the struggle which is going on for existence. Nature's competition is of the keenest kind; the strongest survive, the weakest go to the wall. Even an object so low in the scale of animal creation as a chrysalis assumes a red coat when it is attached to a bright brick wall, and a grey one when it affixes itself to limestone. This inherent power it has in itself, and those individuals which can most cleverly practise deceit in hiding from birds and other enemies survive and reproduce their kind. With regard to instances of variability which come under our immediate notice, the red grouse of our moorlands as already mentioned is a striking example. There can now be no doubt that this is the "willow grouse" of the Scandinavian Peninsula. Our indigenous bird found itself in an insular position, and has changed from white to speckled red so as to conform to the colour of the heather; it has also modified the colour of its eggs to suit the changed conditions of its existence. Had it remained white, it would soon have been wiped out of existence by the peregrine and other of the large falcons. There can be no question that bird and animal or insect dons the colour and form best calculated to protect it. Whether this change is conscious to the creature that practises it is beside the main question, and hardly enters into the issue. The process is invariably slow, but if any "accidental sport" occurs which is likely to be of use, it is tenaciously retained, and progress is made at a bound. Many of our British birds exhibit capital instances of protective colouring, and it is a somewhat striking fact that birds of sombre plumage build open nests, while the brilliantly coloured birds either have covered nests or build in holes in trees.