The ornamental design for a wristwatch, as shown and described.
FIG. 1 is a front elevational view of a wristwatch showing my new design,
the broken-line showings of band ends being environmental only and form no
part of the claimed design;
FIG. 2 is a left side elevational view thereof;
FIG. 3 is a right side elevational view thereof;
FIG. 4 is a top plan view thereof, the bottom plan view being a mirror
image thereof;