  The phenomenon of dynamical quark mass generation is studied in QCD within
the framework of a gauge invariant formalism. An exact relationship is
established between the equation satisfied by the scalar part of the two-point
gauge invariant quark Green's function and the quark-antiquark bound state
equation in the chiral limit. A possible nontrivial solution of the former
yields a massless pseudoscalar solution of the bound state equation with
vanishing total momentum. The result is also corroborated by the corresponding
Ward-Takahashi identity. The problem is explicitly solved in two-dimensional
QCD in the large-$N_c$ limit.
