Originally Posted by lordisaiah
Actually, I was referring to the the episode where they get involved with the events of "The Trouble with Tribbles."
Sorry for that when I was rereading your post i remembered the episode were they went back in time via the orb of time. That point in time the planet trill may not have been part of the Federation. Explaining a trill being on the enterprise in a star fleet uniform roaming the ship would have been difficult.