  A formalism is developed for the partial wave analysis of data on meson
photoproduction off deuterons and applied to photoproduction of $\eta$ and
$\pi^0$ mesons. Different interpretations of a dip-bump structure of the $\eta$
photoproduction cross section in the 1670 MeV region are presented and
discussed. Helicity amplitudes for two low-mass $S_{11}$ states are determined.
