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? 
