STABILITY 31 
great difficulty in detecting, and but for the camera 
we should have had to own that, though the bird 
could hardly dispense with this method of balancing 
and steering, we could get no absolutely conclu- 
sive optical evidence. For fore-and-aft balance the 
means employed vary very much according to the 
build of the particular bird. Long-necked birds can 
move their centre of gravity forward and backward. 
by extending or bending their necks. Ducks and 
Geese usually carry theirs stretched out, Herons 
habitually make a crook in theirs. Long necks 
are usually correlated with long legs, and long legs 
are no less serviceable in the matter of balance. 
This is shown by the fact that the long-legged have 
usually small, short tails, the long legs to some extent 
taking the place of the tail as balancers. A Flamingo, 
to take a conspicuous example, having legs of 
enormous length and a neck to match, has no need 
of much tail to regulate his fore-and-aft balance. A 
very little extension or retraction of legs or neck 
will set matters right if they are going wrong. But 
not only do long legs make a great expanse of tail 
unnecessary for balancing purposes, they must in- 
evitably hamper its movements if it is to be pulled 
downward with a view to checking speed or steering 
to right or left. It may well be that this necessary 
inefficiency of tail is in part the cause of the compara- 
tively clumsy steering of these big, heavy-legged 
birds. 
It can be shown, too, that for purposes of balance 
webbed feet very probably play a part of some 
importance. Not only are they fairly heavy, but 
they can be used as the tail is used, though not so 
