coelom
The body of an earthworm is arranged in a ceolom structure. This means that, in the tube of the worm's body, each organ is arranged inside of another. Most of the coelom is filled by the intestine, which runs the length of the body (Zoo Lab). It's easiest to think of the coelom structure as a kind of "tube within a tube", with the inner tube representing the digestive tract and the outer tube representing the body cavity.