  Low-energy doublet neutron-deuteron scattering is described on the basis of
the triton bound and virtual state parameters - the energies and the nuclear
vertex constants of these states. The van Oers-Seagrave formula is derived from
the Bargmann representation of the S matrix for a system having two states. The
presence of a pole in this formula is shown to be a direct corollary of the
existence of a low-energy triton virtual state. Simple explicit expressions for
the nd scattering length and for the pole of the function $k\cot \delta $ are
obtained in terms of the triton bound and virtual state parameters. Numerical
calculations of the nd low-energy scattering parameters show their high
sensitivity to variations in the asymptotic normalization constant of the
virtual state $C_{v}^{2}$. The $C_{v}^{2}$ value fitted in our model to the
experimental result for the nd scattering length is $C_{v}^{2}=0.0592$.
