THE CHICKEN. 95 



while the forelimbs are profoundly modified to form new 

 organs, the wings. 



We have before us an animal organized for flying, and 

 the more deeply we study its different parts the more 

 new characteristics do we find, these being required by 

 the new mode of locomotion. And, first, the feathers that 

 cover the whole surface of the body are not like hairs, 

 organs only epidermic in nature. Each feather has a 

 stem, hollow at its lower end, solid at its extremity, and 

 this stem has slender, flat beards or barbs, arranged 

 symmetrically on each side. The barbs themselves have 

 smaller barbs, ordinarily hooked at the ends, holding 

 themselves firmly fixed one against the other, and called 

 barbules. 



The name down is given to the very light, soft feathers 

 that are hidden under the true feathers ; these have a 

 very slender stem with many branches, and possess barbs 

 without barbules. Consequently, when a breath of air 

 is blown upon the down the barbs separate one from the 

 others, which cannot take place in true feathers whose 

 hooked barbules hold the barbs together. In the eider 

 duck the down is remarkably developed and exceedingly 

 light, and in all birds that inhabit cold countries there 

 exists under the superficial feathers a great abundance 

 of down, more or less delicate, that is sought for filling 

 pillows and cushions. 



The tectrices are feathers that serve only as a sort of 

 clothing to protect the body from cold and wet, and they 

 are covered with a thin layer of a fatty matter that 

 makes them quite water-proof. The feathers of the 

 upper limbs are enormously developed, and so arranged 

 that they form the surface on which the bird rests while 

 flying. They are called quill-feathers, wing-feathers, or 



