  In this comment we demonstrate that the general conjectures of Fong $et~ al$
on their ${\rm YBa_2Cu_3O_7}$ neutron experiments are realized in concrete
calculations of the neutron scattering structure factor $S({\bf q} , \omega )$
in this material. We make predictions for similar experiments in ${\rm
La_2Sr_{0.15}Cu_{1.85}O_4}$, which yield a different q-structure due to the
different fermiology. Our calculations address both the frequency and
wave-vector dependence of the data and (1) include realistic Fermi surface
effects (2) are compatible with the normal state data and (3) demonstrate the
consistency of a $d$-wave order parameter, in ${\rm YBa_2Cu_3O_7}$ although
they appear to be also compatible with an alternate symmetry specific to the
orthorhombic bi-layer system.
