Cogenitor

A cogenitor was one of the three genders of the Vissian species. Doctor Phlox suggested cogenitors produced an enzyme that enabled the reproductive process. They made up three percent of the population and had a low status, being forbidden to read and go out without supervision. They did not even have their own names and were simply passed around where required. 

Before In a Mirror, Darkly
In the mirror universe, a cogenitor from a Vissian starship accompanied by the ship's chief engineer and Calla when they visited ISS Enterprise (NX-01). Commander Charles Tucker became intrigued with the cogenitor's situation and soon became disturbed by the way the Vissians treated their third gender. Defying both the wishes of the Vissians and Captain Maximilian Forrest, Tucker chose to educate the cogenitor himself after he and Doctor Phlox found it was just as sentient as the other genders. Tucker may have associated this situation with that in the novel The Handmaid's Tale as he used this to teach the cogenitor how to read.. The cogenitor then came under the protection of the Terran Empire after swearing allegiance in front of Commander Jonathan Archer. After Starfleet captured the Vissian ship, the cogenitor was liberated and transferred to a starbase. (Before In a Mirror, Darkly)