Flatworms are hermaphroditic with both male and female reproductive organs. They also have internal fertilization. See Penis Fencing (Behavior Sequences) to learn how the sperm gets delivered. [0:48]

A video exploring tapeworms. See how without eyes or mouths tapeworms latch to the inside of the intestine. Also learn that they produce sperm and eggs by the billions. [1:39]

The flatworm's bilateral body plan has a head with a brain and stereo eyes that enable it to actively hunt. Its mouth and pharynx are in the center of its underside. With no circulatory system, the gut distributes food to all parts of...