Kara tells J'onn that her uncle Jor-El used to say "The son becomes the father and the father the son." This line was spoken by Jor-El (Marlon Brando) in Superman (1978).
First appearance of Mon-El's red and blue Legion suit from the comics.
J'onn had an imaginary friend from a parallel dimension name "Zook", a reference to the DC comic book character that appeared in comic books published by National Periodical Publications (now known as DC Comics) in the 1960s. He was the partner of the superhero J'onn J'onzz, the Manhunter from Mars (now known as Martian Manhunter). Zook's first published appearance was in the story, "The Invaders from the Space Warp" from Detective Comics #311 (January, 1963).
J'onn's childhood imaginary friend is said to come from the 5th Dimension. This is the same dimension that the magical imps Mr. Mxyzptlk (who appeared last season) and Bat-Mite come from. In DC comics, the 5th Dimension is said to be imagination.
The title is a reference to the novel of the same name by Marcel Proust.