Calling Dr. Gillespie (1942)
A plug for the next film in the series, right before "The End"
Bugs Bunny acts out a small bit of dialogue and finishes by saying "Calling Dr. Gillespie!"
During the hangings, Harvey Korman says of a hangee in a wheelchair (representing Lionel Barrymore of the Gillespie films) "ah yes, the Dr. Gillespie killings", in reference to the "death" of the series