Star Trek: Enterprise: Season 2, Episode 22

2 - 22: Cogenitor

The Enterprise crew makes first contact with the Vissians, a species with three genders. Trip meets one of the species' third gender, a Cogenitor, a being used for only breeding purposes. After learning how badly Vissians treat all Cogenitors, Trip attempts to help this Cogenitor, even though it directly interferes with Vissian culture.