  The eight-vertex model at the reflectionless points is considered on the
basis of Smirnov's axiomatic approach. Integral formulae for form factors of
the eight-vertex model can be obtained in terms of those of the eight-vertex
SOS model, by using vertex-face transformation. The resulting formulae have
very simple forms at the reflectionless points, and suggests us the explicit
expressions of the type II vertex operators of the eight-vertex model.
