Nematode Mouth Pharynx Intestine Anus 消 Earthworm Crop Gizzard Pharynx Mouth Intestine Anus 化糸统的演化 Intestine Salamander Stomach Cloaca Anus Mouth Liver Pancreas esophagus FIGURE 48.3 The one-way digestive tract of nematodes, earthworms, and vertebrates. One-way movement through the digestive tract allows different regions of the digestive system to become specialized for different functions消化系统的演化