Flatworms have both male and female sex
organs in the one animal. If you think about it, that's a great way to
be. If you're rare and you're looking for a mate and you're traveling
alone, you don't have to meet another female or another male. You just
have to meet another one. -- Dr. Leslie Newman, Marine Biologist at Southern Cross University, Lismore NSW Australia

http://www.pbs.org/kcet/shapeoflife/episodes/hunt_explo2.html