For example, if creatures without the necessary structures for flight jumped out of trees, they would crash to the ground rather than "flying through the sky".
Snakes aren't typically thought of as having "the necessary structures for flight," but there is a species of snake in Southeast Asia that "jumps" out of trees - like ten meters up in a tree - and glides to a safe landing maybe ten or twelve meters away from the tree of departure. This critter has a somewhat flattish body, and wriggles in a horizontal fashion as it falls, thereby making an airfoil. No crash, just a clean escape. And no specialized structures, either.
Edit: they have a webpage!
http://www.flyingsnake.org/
This message has been edited by Coragyps, 09-03-2004 03:58 PM