  Various theories of spinning particles are interpreted as realizing elements
of an underlying geometric theory. Classical particles are described by
trajectories on the Poincare group. Upon quantization an eleven-dimensional
Kaluza-Klein type theory is obtained which incorporates spin and isospin in a
local SL(2,C) x U(1) x SU(2) theory with broken U(1)x SU(2) part.
