Generalized Action Principle and Superfield Equations of Motion for d=10 D-p-branes

The action for the D=10 type II Dirichlet super-p-branes, which has been obtained recently, is reconstructed in a more geometrical form involving Lorentz harmonic variables. This new (Lorentz-harmonic) formulation possesses kappa-symmetry in an irreducible form and is used as a basis for applying a generalized action principle that provides the superfield equations of motion and clarifies the geometrical nature of the kappa-symmetry of these models. The case of a Dirichlet super-3-brane is considered in detail.