"U-Ravana Story" joke

This happened way back in 1950's. It's the first day our famous U-Ravana took his family
to Colombo to see the tallest building in Ceylon - the famous Ceylinco House.
They were amazed by everything they saw -- especially the elevator at one end of the
lobby. The son of U-ravana, then a little boy of 10 years, asked, "What's this, Appachchi?"
to which Mr. U-Ravana responded, "Putha, I have never seen anything like this in my life,
I don't know what it is!"
While the son and the father were watching in wide-eyed astonishment, an old lady in a
wheel chair rolled up to the moving walls and pressed a button. The walls opened and the
lady rolled between them into a small room. The walls closed and the son and father
watched small circles of lights above the walls light up. They continued to watch the
circles light up in the reverse direction. The walls opened again, and a voluptuous
24-year-old woman stepped out.
Mr. U-Ravana turned to his son and said, "Go get your Amma."