  There exists a class of cosmic strings that turn matter into antimatter
(Alice strings). In a GUT where the unbroken gauge group contains charge
conjugation ($C$), such strings form when a phase transition renders $C$ a
discrete symmetry. They become boundaries of domain walls at a later,
$C$-breaking transition. These `Alice walls' are cosmologically harmless, but
can play an important role in baryogenesis. We present a three-generation toy
model with scalar baryons, where a quasi-static Alice wall (or a gas of such
walls) temporarily gives rise to net baryogenesis of uniform sign everywhere in
space. This becomes a permanent baryon excess if the wall shrinks away early
enough.
  We comment on the possible relevance of a similar mechanism to baryogenesis
in a realistic $\soten$ unification model, where
  Alice walls would form at the scale of left-right symmetry breaking.
