146 THE STORY OF THE BIRDS. 
free and opposable) at the demands of better swim- 
ming, and the flamingo’s bill is bent down and fringed 
on its upper prong only, not that he should feed as if 
standing on his head, but because he did do it. 
All these cases partake of the same nature generally 
as the development of the bird’s wing: not so much 
that it might fly as that it attempted it. Nature does 
her best for any creature in its chosen environment. 
If the snake insists on wriggling instead of running on 
legs, she takes away the useless organs, and adapts 
the creature by alterations and neat adjustments of 
other parts for his new mode of motion. If creatures 
haunt caves, then useless eyes go; if they ride on 
others, they lose legs and wings; and if they haunt 
the stomachs of others, they may even lose their 
stomachs. 
But there are other instances where the task 
seems to come about because the tool is ready at 
hand. Certain habits are set up because the ability, 
capacity or means for practicing them are present. 
Thus the practice of the vultures, petrels and other 
organisms in ejecting disgusting food for defense is 
the result of the capacity for doing it, which is purely 
incidental to their manner of feeding. 
So likewise a creature in a new environment may 
earry with it an old tool of some ancestor, which was 
quite useful in the former state for a certain purpose, 
but may remain for a while or forever a useless ves- 
tige in the present. Again, it may be used here for 
another purpose and retained in this new capacity ; 
and its presence may set up new habits. Let us 
