INTRODUCTORY. 5 



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 con- 

 structed 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 fore- 

 limbs 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 



