  We study matrix string scattering amplitudes and matrix string instantons on
a marked Riemann surface in the limit of a vanishing string coupling constant.
We give an explicit parameterization of the moduli space of such instantons. We
also give a description of the set of fermionic supermoduli. The integration
over the supermoduli leads to the inclusion of picture changing operators at
the interaction points. Finally we investigate the large N limit of the measure
on the instanton moduli space and show its convergence to the Weil-Petersson
measure on the moduli space of marked Riemann surfaces.
