" The one on the left," Worthil said, "is a male, carrying the testes and penis. The middle one is equipped with a kind of reversible vagina, and ovaries. The vagina turns inside-out to implant the fertilised egg in the third sex, on the right, which has a womb. The one in the middle is the dominant sex."

Gurgeh had to think about this. "The what?" he said. "

― Iain M. Banks