RED-BREASTED MERGANSER. 271 



ches from the mouth it swells out to four times its common di- 

 ameter, continuing of that size for about an inch and a half. 

 This swelling is capable of being shortened or extended; it then 

 continues of its first diameter for two inches or more, when it 

 becomes flattish, and almost transparent for other two inches; 

 it then swells into a bony labyrinth of more than two inches in 

 length by one and a half in width, over the hollow sides of which 

 is spread a yellowish skin like parchment. The left side of this, 

 fronting the back of the bird, is a hard bone. The divarications 

 come out very regularly from this at the lower end, and enter 

 the lungs. 



The intention of Nature in this extraordinary structure is 

 probably to enable the bird to take down a supply of air to sup- 

 port respiration while diving; yet why should the female, who 

 takes the same submarine excursions as the male, be entirely 

 destitute of this apparatus? 



