complete digestive tract—one with two openings, a mouth and an anus. In these organisms incoming food can move in one direction from mouth to anus through a tubular system, which can be divided into a series of distinct sections or chambers, each specialized for a different function. As the food passes along this assembly line, it is acted upon in a different way in each section. The sections may be variously specialized for mechanical breakup of bulk food, temporary storage, enzymatic digestion, absorption of the products of digestion, reabsorption of water, storage of wastes, and so on. The overall result is a much more efficient digestive system, as well as a potential for special evolutionary modifications fitting different animals for different methods of obtaining nutrients. The evolution of a complete digestive tract was a major evolutionary event in the evolution of life.