  A two dimensional anomaly cancellation argument is used to construct the
SO(32) heterotic and type IIB membranes. By imposing different boundary
conditions at the two boundaries of a membrane, we shift all of the two
dimensional anomaly to one of the boundaries. The topology of these membranes
is that of a 2-dimensional cone propagating in the 11-dimensional target space.
Dimensional reduction of these membranes yields the SO(32) heterotic and type
IIB strings.
