The Naked Time
Season 1, Ep. 47
Space still contains infinite unknowns, but we know we’re talking about Season 1, Episode 4
Operation -- Annihilate!
Season 1, Ep. 50
Flying parasites infest the last episode of the first season.
The Omega Glory
Season 1, Ep. 49
There's no serum! There are no miracles! There's no immortality here! Just season 2, episode 23.