optics - Why not have the diaphragm in camera body instead of the lens?

Why is the diaphragm to control the amount of light entering the camera typically in the lens and not the camera body itself?

Answer

Most lenses have one or more lens elements behind the diaphragm also. I actually haven't seen one that doesn't.

http://en.wikipedia.org/wiki/File:Tessar.png

From: http://en.wikipedia.org/wiki/Photographic_lens_design