Hydra to open its mouth and to curl the tentacles towards it. The food is put into the mouth and digestion begins. The gut of Hydra is simply the hollow cavity within the body and has only one opening, the mouth. Enzymes are produced by special cells in the endodermis and released into the gut cavity. These enzymes begin to break down the food into smaller particles. Other lining cells have long hair-like flagella that wave about and keep the contents of the gut well mixed. A further type of lining cell acts rather like an amoeba and engulfs small particles. Digestion is completed inside these cells in food vacuoles and the products are diffused over the rest of the body. Undigested food is passed out of the cells into the gut cavity and from there to the outside through the mouth