  We derive and study a class of cosmological and wormhole solutions of
low-energy effective string field theory. We consider a general
four-dimensional string effective action where moduli of the compactified
manifold and the electromagnetic field are present. The cosmological solutions
of the two-dimensional effective theory obtained by dimensional reduction of
the former are discussed. In particular we demonstrate that the two-dimensional
theory possesses a scale-factor duality invariance. Euclidean four-dimensional
instantons describing the nucleation of the baby universes are found and the
probability amplitude for the nucleation process is given.
