180 



ANATID.E. 



seen from behind, the enh\rgement in this, as in most of the 

 other species, being on the left side. The object here in- 

 tended is to show the course of the air from each lobe of the 

 lungs to the single portion of the tube of the windpipe. The 

 column of air on the right side in the bird, and in the repre- 

 sentation, goes direct from the right lobe of the lungs to the 

 tracheal tube ; but the column of air on the left side, on 

 passing through the bronchial tube, is opposed by the de- 

 scending edge, and being divided by it, a portion is sent in 

 circles round the inner surface of the cavity before it becomes 

 united with the air from the other lobe in the tube common 

 to both. A compound tone of voice is thus produced by 

 which wild-fowl shooters can distinguish males from females, 

 of the same species, in the darkest night, Avhenever the birds 

 utter their note, and this they frequently do, apparently for 

 the purpose of keeping together. The resemblance to the 

 reed or other mouth-piece, and the edge opposed to its inner 

 orifice, to produce vibration, in some musical wind instru- 

 ments, will be obvious. 



