Flatworms are flattened, leaf-like forms living in damp places on land, in freshwater streams of ponds, or along the seacoast while a variety of other species are parasitic. The free forms are usually small, barely reaching a length greater than five or seven cetimeters (2 to 3 inches). Some of the parasitic species attain the great length of six to thirteen meters (20 to 40 feet). This shows the nervous system of the flatworm.
Winchell, Alexander Sketches of Creation (New York, NY: Harper & Brothers, 1870)