Learn about the anatomy of the flatworm in this video segment. Flatworms look simple, but they were the first animals to evolve a bilateral body plan with a head, a brain, and stereo senses enabling them to actively hunt. Flatworms are hermaphroditic with both male and female reproductive organs, and have internal fertilization. With no circulatory system, their gut distributes food to all parts of their bodies. Learn more about the structure and evolution of this fascinating creature with The Shape of Life.