430 NOTE. 



Reverting to page 306, we may state that the connexion of the 

 structural peculiarities of the trachea in so many of the natatorial birds, 

 with the mode of feeding, is very problematical; inasmuch as in the 

 males only, with certain exceptions, are these peculiarities displayed. 

 Adverting to the ducks, we may observe, that in both sections the 

 trachea presents in the male varied singularities. Many have the tube 

 contracted, as the Anas rufina; in others it is more dilated in the centre 

 than towards the beginning and termination. Nor is it to the ducks 

 that these variable peculiarities are restricted, for they run more or less 

 through the geese and the mergansers. 



But the structural singularities (so far, at least, as the ducks are con- 

 cerned) do not end here. In addition to the dilatations and contractions 

 of the tube, it is divided, in the males of many species, at its bifurcation, 

 into two bronchial tubes just within the chest, with a hollow drum, or 

 leulla, varying in size and figure, generally composed of delicate bone, 

 but sometimes of bone and membrane. We may refer to the male of the 

 common duck, of the gadwall, of the king- duck, of the musk-duck, &c. 



Passing to the swans, we find strange convolutions in the trachea, 

 before it enters the chest. In the tame swan indeed, and in the Polish 

 swan, the trachea is simple, and devoid of convolutions, as it is also in 

 the black swan of Australia ; but in Bewick's swan, and in the Hooper's, 

 or whistling swans, the trachea forms a vast segmoid flexure or loop, 

 received into the keel of the breast-bone, which is hollowed for its recep- 

 tion : here the trachea extends backwards, between to the plates of the 

 keel, nearly throughout its whole extent, then turning suddenly upon 

 itself, it passes forwards, and emerging, sweeps round the apical portion 

 of the merrythought, and so again turning back, enters the chest, and 

 there gives off its long bronchial tubes, one to each lobe of the lungs. 

 This peculiarity is not confined to the males of the swans in question, 

 but the extent in the female (and young male) to which the trachea 

 enters into the keel of the breast-bone is not so considerable as in the 

 adult male. M. 



I'KIVIKD BY HAKttlSON AND SONS, 

 LONDON QAZKTTK OFF1CK, ST. MARTIN *S LANE. 



