We claim the ornamental design for an incubator, as shown and described.
FIG. 1 is a front perspective view showing an incubator of the present invention;
FIG. 2 is a rear perspective view thereof;
FIG. 3 is a front view thereof;
FIG. 4 is a rear view thereof;
FIG. 5 is a left side view thereof;
FIG. 6 is a right side view thereof;
FIG. 7 is a top plan view thereof;
FIG. 8 is a bottom view thereof;
FIG. 9 is a front perspective view with a cover being opened; and,
FIG. 10 is another front perspective view with the cover being opened and a cartridge shown inside by broken lines.
The broken lines depicting a cartridge in FIG. 10 represent an environment, and the remaining broken lines depict portions of the incubator that form no part of the claimed design. The broken lines and the unshaded surfaces form no part of the claimed design.