  We report the measurement of spin waves in the bilayer colossal
magnetoresistive manganites La(2-2x)Sr(1+2x)Mn2O7 with x=0.30, 0.35 and 0.40.
For x=0.35 and 0.40 the entire acoustic and optic dispersion relations are
reasonably well described by those for a bilayer Heisenberg Hamiltonian with
nearest neighbour exchange only. The in-plane coupling is only weakly dependent
on x, but the coupling between the planes of a bilayer changes by a factor of
four. The results directly reveal the change from mixed and character of the
orbitals to mostly character with increasing hole concentration.
