The Breath of a Bird 173 



of song is not solved. The marvel of the Canyon Wren's 

 melody becomes but the more wonderful; the voice of 

 the Seriema, carrying over a mile, and the never-to-be- 

 forgotten evening song of the Solitaire only impress us 

 with the failure of the scalpel and microscope to explain 

 more than superficially the varied expressions of life. 



Lungs and Air-sacs 



At the beginning of this chapter a bird was compared 

 to an insect, and the reason will now be apparent. The 

 body of an insect is aerated by means of an intricate sys- 

 tem of tubes ramifying throughout the body, which in 

 many instances are connected with air-sacs. The com- 

 parison with a bird is not to its lungs, which are small 

 and compact, but to a series of nine air-sacs, distributed 

 through much of the body, four pairs, and two which 

 have coalesced into one. 



When a bird is dissected, the thin membranous walls 

 of these air-cavities are collapsed and rather difficult 

 to make out, being very similar in appearance to other 

 connective tissues of the body. But if we insert a small 

 blowpipe into the trachea of a dead bird, tie it tightly 

 about with a piece of string and blow into it, all the air- 

 sacs will become distended and bladder-like and can 

 easily be made out. It is remarkable how closely these 

 sacs fit around the viscera and muscles, occupying every 

 crevice and filling the whole body of the bird with air, 

 thus reducing its specific gravity, and making it a crea- 

 ture literally "of the air." There is sometimes a layer of 



