The Earth has been scheduled for destruction, but Arthur Dent and Ford Prefect have snuck onto the alien craft.
Theme: Exploration, Symbol: A towel, which all good hitchikers need.
The Earth has been destroyed, but Ford and Arthur are already on the spaceship.
Theme: Discovery Authur's primitive human mind finds out that aliens, with technology much more advanced than ours, exist.
Themes: Language / Communication, knowledge. Ford and Arthur are trying to hid from the aliends, and are using fish that they put in their ear to translate the speech.
The fact that this was showed in book is clear satire and humor, meant to question the reader on why this was shown.
The answer to life, the universe, and everything: 42. Clear satire, because we don't know what the question is, just the answer.
In this final comic; Arthur and Ford are on the Heart of Gold with Zaphod, but two missles are incoming and were about to blow them up. But, with the improbability drive, Arthur accidently saves everyone by turning the missles into a whale and some flowers.
This shows the theme of absurdity and the humor in this book, by also showing the odds of this occuring.