We claim the ornamental design for the mannequin, as shown.
FIG. 1 is a perspective view of a mannequin, showing our new design;
FIG. 2 is a front elevational view thereof;
FIG. 3 is a left side elevational view thereof;
FIG. 4 is a right side elevational view thereof;
FIG. 5 is a rear elevational view thereof;
FIG. 6 is a rear elevational view thereof with the broken lines for the support structure removed to show the complete design outline;
FIG. 7 is a top plan view thereof;
FIG. 8 is a bottom plan view thereof; and,
FIG. 9 is a bottom plan view thereof with the broken lines for the support structure removed to show the complete design outline.
The broken lines contained in the figures show the support structure for the mannequin, are included for the purpose of illustrating environmental structure, and form no part of the claimed design.