The ornamental design for a syringe, as shown and described.
FIG. 1 is a front elevational view of a syringe embodying a modification of my invention with the elevational view from left, right, and rear being identical to the front view;
FIG. 2 is a top plan view of the embodiment shown in FIG. 1; and,
FIG. 3 is a bottom plan view of the embodiment shown in FIG. 1.