402 A HISTORY OF BIRDS 



which fits into a hollow in the symphysis of the furcula, but 

 the voice of this bird is not peculiar. 



In the Storks the bronchi are of remarkable length, and in 

 the Black Stork {Ciconia nigra) take an co -shape twist before 

 entering the lungs, while in one species of Spoon-bill {Platalea), 

 and in the Tantalus Stork (Tantalus ibis), the trachea is coiled 

 up into an 8-shaped loop, but these birds are practically silent. 

 In both sexes of the Whooper, Trumpeter and Bewick's 

 Swans and in some Cranes the windpipe is received into the 

 keel of the breast-bone, which has been enlarged to form a hollow 

 chamber for its reception. Here again we have a precisely 

 similar modification independently acquired by two very distinct 

 groups, but differing in this — that in the Swans the loop of the 

 windpipe passes under the furcular symphysis, while in the 

 Cranes it passes above this, as may be seen in 111. 23. Here the 

 coils seem undoubtedly to be used for the purpose of increasing 

 the volume of the voice, but the Cranes so provided do not appear 

 to call more loudly than species not so furnished. 



Among the Ducks some very remarkable modifications are 

 to be met with, and these show a very interesting series of in- 

 creasing complexity. In the Common Mallard {Anas boschas) 

 for example, the lower end of the trachea develops on its left 

 side a large osseous, thin-walled, bulbous chamber immediately 

 over the bronchus, while the right side of the tube remains 

 unmodified. Varying chiefly in size, this same chamber will be 

 found in the males only of all the fresh-water surface-swim- 

 ming Ducks, and is generally regarded as an important factor 

 in the production of the voice. If this be true it is curious that 

 in the Mallard, for example, the males have but a low hoarse 

 note, while the call of the female — which lacks this resonating 

 chamber, if such it is — is loud. In the Diving-ducks this 

 chamber becomes enormously increased in size, and changes 

 much in shape. No longer spherical, it becomes now discoid, 

 consisting of an osseous ring of bone, wider at the base than the 

 top, and supporting a tense but delicate sheet of membrane. 

 Usually, the centre of the disc is crossed by an arcuate bar, 

 which looks as though it had been developed for the sake of 

 strengthening the disc. It is more probable, however, that this 

 bar and the short " stays " of bone between the outer rim and 

 the bar, are the last remnants of a continuous wall of bone such 



