Flatworms prefer same-size mates. Beth Tyler 05.25.01 In many animals, males and females look different. But flatworms, like other worms, are hermaphrodites. That means each worm has both male and female parts. Two scientists were interested in how flatworms Dugesia gonocephala chose another flatworm to mate with. They had observed them flattening their bodies and rolling over each over before mating. They thought this allowed the flatworm to figure out the size of another flatworm. They hypothesized that flatworms used this information on size to decide who to mate with.     To test their hypothesis, they collected flatworms from underneath rocks near streams, where flatworms live. Then they put three short flatworms and three long flatworms together. As they had seen before, the flatworms flattened their bodies and rolled over each other. After that, flatworms mated with worms that were closer to their own size. The scientists concluded that flatworms role over each other to find out how big the other flatworm is, then use that information to mate with same-sized worms.   Vreys, C., and N. K. Michiels. 1997. Flatworms flatten to size up each other. Proceedings of the Royal Society of London Series B 264: 1559-1564. ©2001 The Aurora Collection, Inc. All Rights Reserved. Site Development by: Interactive Multimedia. Inc.