E. hortensis is a hermaphrodite, it has both male and female reproductive organs. In mating, the less strong partner is forced in to the female role which is more expensive in terms of biological reproduction costs, for a sperm cell is generally less massive and energy-demanding than an ovum ("egg cell"), which is the female reproductive cell (gamete) in anisogamous organisms. Two worms join clitella, the large, lighter-colored bands which contain the worms' reproductive organs, and which are only prominent during the reproduction process.