blood is warm, and lower than the beasts in that they do not suckle their young but lay eggs. There are other points in which they differ from both. They have no lips nor teeth, their mouths being encased in horn and consolidated into a beak. That they are clothed with feathers we all know, but few have any idea of the properties of that wonderful garment. The long, stiff feathers of the wing, called "quills," are little oars, or fans, for beating the air, and those of the tail form an expanding and collapsing rudder; but the body clothing is of softer plumes, so constructed and so arranged as to combine all the diverse qualities of all the fabrics that man has ever woven for his own comfort or adornment. Each feather is at its point a scale, or leaf, smooth, soft, porous and yet waterproof; but at the base it is dishevelled and downy. Each keeps its place and overlaps the next so as to form a smooth and even surface and an unbroken pattern; but the down is underneath. When the bird goes to bed it shakes up its plumage and is wrapped in an eiderdown quilt; but startle it and in an instant every feather is pressed firmly down and the compact little body is prepared to cleave the air as a scale-clothed fish cleaves the water.
But the most vital difference between birds and all other vertebrate animals lies in the fact that their forelimbs are converted into organs of flight. This handicaps them in many ways, as any one may see for himself by watching a squirrel and a sparrow dealing with a crust of bread: but it admits them to a realm which is closed against fourfooted creatures. The sky is their territory and the trees arc their
