  The doping, temperature and energy dependence of the dynamical spin structure
factors of the underdoped lanthanum cuprates in the normal state is studied
within the t-J model using the fermion-spin transformation technique.
Incommensurate peaks are found at $[(1\pm\delta)\pi,\pi]$,
$[\pi,(1\pm\delta)\pi]$ at relatively low temperatures with $\delta$ linearly
increasing with doping at the beginning and then saturating at higher dopings.
These peaks broaden and weaken in amplitude with temperature and energy, in
good agreement with experiments. The theory also predicts a rotation of these
peaks by $\pi/4$ at even higher temperatures, being shifted to $[(1\pm
\delta/\sqrt{2})\pi,(1\pm \delta/\sqrt{2})\pi]$.
