  For an even dimensional, compact, conformal manifold without boundary we
construct a conformally invariant differential operator of order the dimension
of the manifold. In the conformally flat case, this operator coincides with the
critical {\sf GJMS} operator of Graham-Jenne-Mason-Sparling. We use the
Wodzicki residue of a pseudo-differential operator of order $-2,$ originally
defined by A. Connes, acting on middle dimension forms.
