Depending on the organism, the digestive system can include the mouth, alimentary canal or gastrovascular cavity, esophagus, stomach, small intestine, large intestine, and anus. The mouth is the opening through which food is ingested. In animals with a second opening for elimination, the digestive system contains an alimentary canal, essentially a tube allowing for the passage of food from the mouth to the anus. In contrast, animals with only one opening have a gastrovascular cavity that serves as the site of digestive activities.