The more complex animals have a tube-within-a-tube design. There is an inner tube, the gut, open at opposite ends (the mouth at one end, the anus at the other). The tube is inside another space called the body cavity, or coelom. An earthworm shows this arrangement very well. If you aren’t confused branchings and changes in bore of the inner tube, you will find the same plan in yourself. All the so-called higher animals have it. The gut is the digestive canal; the coelom is the cavity that remains when you cut a beef or a chicken down the middle and spill out its innards.