BIRDS OF OLD 71 



of the feathered race, the exclusive prerogative 

 of the bird being not flight but feathers ; no 

 bird is without them, no other creature wears 

 them, so that birds may be exactly defined in 

 two words, feathered animals. Reptiles, and 

 even mammals, may go quite naked or cover 

 themselves with a defensive armor of bony 

 plates or horny scales ; but under the blaze of 

 the tropical sun or in the chill waters of arctic 

 seas birds wear feathers only, although in the 

 penguins the feathers have become so changed 

 that their identity is almost lost. 



So far as flight goes, there is one entire order 

 of mammals, whose members, the bats, are 

 quite as much at home in the air as the birds 

 themselves, and in bygone days the empire of 

 the air belonged to the pterodactyls ; even frogs 

 and fishes have tried to fly, and some of the 

 latter have nearly succeeded in the attempt. 

 As for wings, it may be said that they are 

 made on very different patterns in such animals 

 as the pterodactyl, bat, and bird, and that 

 while the end to be achieved is the same, it is 

 reached by very different methods. The wing 

 membrane of a bat is spread between his out- 



