Annoyed by the professor of anatomy who liked to tell "naughty" stories during class, a group of female students decided that the next time he started to tell one, they would all rise and leave the room in protest.
The professor, however, got wind of their scheme just before class the following day, so he waited his time.
Then, halfway through the lecture, he began.
"They say there is quite a shortage of prostitutes in France."
The girls looked at one another, arose and started for the door.
"Young ladies," said the professor with a broad smile, "the next plane doesn't leave till tomorrow afternoon."