  For a tight binding model with nearest neighbour attraction and a small
orthorhombic distortion, we find a phase diagram for the gap at zero
temperature which includes three distinct regions as a function of filling. In
the first, the gap is a mixture of mainly $d$-wave with a smaller extended
$s$-wave part. This is followed by a region in which there is a rapid increase
in the $s$-wave part accompanied by a rapid increase in relative phase between
$s$ and $d$ from 0 to $\pi$. Finally, there is a region of dominant $s$ with a
mixture of $d$ and zero phase. In the mixed region with a finite phase, the
$s$-wave part of the gap can show a sudden increase with decreasing temperature
accompanied with a rapid increase in phase which shows many of the
characteristics measured in the angular resolved photoemission experiments of
Ma {\em et al.} in $\rm Bi_2Sr_2CaCu_2O_8$
