  We have studied by small angle neutron scattering the evolution induced by
the application of magnetic field of the coexistence of ferromagnetism (F) and
antiferromagnetism (AF) in a crystal of Pr$_{0.67}$Ca$_{0.33}$MnO$_3$. The
results are compared to magnetic measurements which provide the evolution of
the ferromagnetic fraction. These results show that the growth of the
ferromagnetic phase corresponds to an increase of the thickness of the
ferromagnetic ''cabbage'' sheets.
