BtEDS. 307 



Fig. 242). At the upper part of the wind-pipe is an organ 

 (the glottis, or superior larynx) by which the size of the aper- 

 ture seems to be regulated. At the lower part is placed the 

 true organ of voice in birds (the inferior larynx); and, in all 

 those which possess the vocal powers in the highest perfection, 

 this part is furnished with five pair of nerves. " The tube of 

 the wind-pipe," says Mr. Yarrell, '' is composed of two mem- 

 branes, enclosing between them numerous cartilaginous or bony 

 rings, forming a cylinder more or less perfect from end to end."* 

 The tube differs in its length, its diameter, and its substance, 

 in different species ; and in some it exhibits convolutions which 

 modify its powers. " The principle upon which the organs of 

 voice in birds is founded, is that which prevails in wind instru- 

 ments generally; the notes in the ascending scale being pro- 

 duced by a corresponding contraction of the diameter or the 

 length of the tube, and vice versdy 



Such is the description given by physiologists of the mecha- 

 nism which produces the loud note of the Wild Swan, the 

 booming of the Bittern, the cawing of the Rook, the hooting 

 of the Owl, and the wild screams which, heard amid the native 

 haunts of the sea-fowl, harmonize with the surging sea. 

 Birds, as we all know, can be taught to imitate the tones of 

 the human voice ; nor is this limited to the Parrot ; the power 

 is enjoyed, among our native birds, by the Raven, the Magpie, 

 the Jay, and the Starling. So distinctly have Ravens been 

 taught to articulate short sentences, that one living at Chatliam, 

 " in the vicinity of the guard-house, has more than once turned 

 out the guard, who thought they were called bv the sentinel on 



duty."t 



The power of imitation reaches, perhaps, its highest per- 

 fection in the Mocking-bird of America. So perfect is his 

 performance, that not only the experienced ear of the fowler is 

 deceived, but even birds themselves are imposed upon. In a 

 domesticated state he finds equal scope for the versatility of 

 his powers, and his doings have been most graphically recorded 

 by Wilson, in his American Ornithology : — " He whistles for 

 the dog ; Caesar starts up, wags his tail, and runs to meet his 

 master. He squeaks out like a hurt chicken, and the hen 

 hurries about, with hanging wings and bristled feathers, cluck- 

 ing to protect its injured brood. The barking of the dog, the 



* British Birds, vol. ii p. 71. 



t Quoted by Mr. Yarrell, from Swainson and Kichardson. 



X 



