  We consider the double-exchange for systems in which doped electrons occupy
degenerate orbitals, treating the realistic situation with double degenerate
$e_g$ orbitals. We show that the orbital degeneracy leads in general to
formation of anisotropic magnetic structures and that in particular, depending
on the doping concentration, the layered magnetic structures of the A-type and
chain-like structures of the C-type are stabilized. The phase-diagram that we
obtain provides an explanation for the experimentally observed magnetic
structures of some over-doped (electron-doped) manganites of the type
Nd$_{1-x}$Sr$_x$MnO$_3$, Pr$_{1-x}$Sr$_x$MnO$_3$ and Sm$_{1-x}$Ca$_x$MnO$_3$
with $x > 0.5$.
