10 
GUIDE TO THE 
captive bird ; the wily Mexican, however, drives off the birds 
and appropriates the fishes for his own use. Besides be¬ 
ing so thoroughly aquatic in their habits, that they 
progress with difficulty on land and with an ungainly 
waddle, they are nevertheless possessed of great powers 
of flight due to the great size of their wings and to 
the buoyancy of their bodies. This latter feature of their 
organization is effected by the air which they breathe 
finding access not only to their bones but into the tissue 
which underlies their skin. It is only, however, in the last 
mentioned particular that they differ from other birds in 
the provision for flight, because it is a peculiarity of the 
feathered tribe that their lungs open internally into large 
air-sacs. These are generally nine in number, two in the 
abdomen, four in the chest, two in the neck, and one 
between the branches of the merry-thought or collar-bone. 
These air-sacs communicate with the air-cells in the bones 
of the bodies of the birds ; the bones of the head only 
receiving the air which they contain from the ear and 
the cavities of the nose. 
The Swans, Ducks, and Geese belong to the family Anati- 
dee. There are usually several representatives of the common 
White Swan, Cygnus olor, also known as the mute-swan. 
It is generally distributed over Europe and occurs in the 
western portion of Asia and has been killed in Sindh. 
The other white swans are the Hooper swan, Bewick’s 
swan, and the Trumpeter swan. 
The Black-necked Swan, Cygnus m'gn'co/lis, is peculiar 
to the Antarctic regions of South America, whilst the Black 
Swan, Cygnus atratus , of which there are some specimens 
in this pond, is found only in Australia. 
The chief characteristics of Swans are their greatly 
