The BCS model and the off-shell Bethe ansatz for vertex models

We study the connection between the BCS pairing model and the inhomogeneous vertex model. The two spectral problems coincide in the quasiclassical lim it of the off-shell Bethe ansatz of the disordered six-vertex model. The la tter problem is transformed into an auxiliary spectral problem which corres ponds to the diagonalization of the integrals of motion of the BCS model. A generating functional whose quasi-classical expansion leads to the constan ts of motion of the BCS model, and in particular the Hamiltonian, is identi fied.