  We consider the partition function of a general vertex operator algebra $V$
on a genus two Riemann surface formed by sewing together two tori. We consider
the non-trivial degeneration limit where one torus is pinched down to a Riemann
sphere and show that the genus one partition function on the degenerate torus
is recovered up to an explicit universal $V$-independent multiplicative factor
raised to the power of the central charge.
