INTRODUCTION. 



'HE most conspicuous external characteristic by which the Birds are distinguished 

 from all other inhabitants of earth, is the feathery robe winch invests their bodies, 

 and which serves the double purpose of clothing and progression. For the first 

 of these two objects it is admirably adapted, as the long, slender filaments of the 

 feathers are not only in themselves indifferent conductors of heat, hut entangle 

 among their multitudinous fibres a considerable amount of air, which resists the 

 ingress or the egress of external or internal heat, and thus preserves the bird in a 



moderate temperature through the icy blasts of winter or the burning rays of the summer sun. 



A similar function is discharged by the furry coats of many mammalia ; but the feathers serve 



Vol. 11.— 1. 



