Another early toupee sighting.
Link
There've been enough eyewitness accounts that there never has been any doubt that Shatner wore a rug during TOS, but there you are.
One of Perry’s most vivid memories of filming ["Tomorrow Is Yesterday"] had to do with what happened before the cameras began rolling for the day. “The unusual thing, but I have to say this because I remember it,” said Perry. “The very first day going into makeup I was in the makeup room and [William] Shatner was a couple of chairs down. I remember looking over and I was very shocked because they were putting his toupee on. I said, ‘Wait a minute. He’s a young man.’ At that time he was very young and I thought, ‘Well, that’s interesting.’ I didn’t know at that time whether they were doing it because of the character. Then I heard later on that he’d been wearing a toupee for a long, long time.
Link
There've been enough eyewitness accounts that there never has been any doubt that Shatner wore a rug during TOS, but there you are.