Ornithopters

I noticed that the Astrogator's Guide to Diaspora contained a couple
of references to ornithopters.  What are these?  I remember them from
Frank Herbert's _Dune_, where they seemed to be desert gliders which
became airborne by either VTOL or perhaps hopping.  So can anyone
describe an ornithopter, or point to the location of a good descrip-
tion?

Thanks.

Chuck Hamilton                                           [email removed]

The MITRE Corporation               "Two days ago I saw a vehicle that
Washington C3 Center                 would 'aul that tanker.  You want
Dept. W036 / Mail W656               to get outa here..?  talk t' Me."
[address removed]
[phone removed]                                     _The Road Warrior_