Alimentary Canal

the digestive tract. In the simplest form, as in the hydra, it is co-extensive with the body-cavity. In the higher animals the alimentary canal is separated from the body-cavity, and there are various enlargements, divisions, and valves in the way of pouches, crops, gizzards, stomachs, and intestines. The study of anatomy and physiology is much simplified if we bear in mind that all these are but modifications of the simple form. The alimentary canal or digestive tract is a tube extending through the body. In the simpler animals, as in the hydra, the process of digestion is carried on within the body-cavity, and there is no tract or tube especially set apart for this work. In the earthworm, however, the alimentary canal is separate from the body-cavity, and consists of a straight tube which is about the same diameter throughout the body. In the higher animals, as in birds and mammals, the tube is much twisted and doubled on itself, so that it is usually much longer than the entire body. In the higher animals, also, it varies in diameter, because of enlargements into pouches, crops, or stomachs. At certain points growths or organs of various sizes, called glands, are connected with it by means of small tubes called ducts. These glands produce and pour into the alimentary canal fluids and juices which aid in digestion. In man the alimentary canal consists of the mouth, the gullet, the stomach, the large and small intestine, and the rectum. Attached to one part of the intestine is the vermiform appendix, a small blind sac, which, when inflamed, is the cause of the disease called appendicitis. See Amoeba; Sponge; Earthworm; Camel; Bird; Cud-Chewers; Ostrich