Use Ending Stitch edit box to select stitches within an Object. Ending Stitch is last stitch of selection. First stitch is given by Initial Stitch. Selection is drawn in red color. It may be cut out by Split command, and then manipulated as independent Object. This edit box is enabled in Select Mode only, in case there is just one Object selected.
Another way of stitches selection is to use Freehand Select Mode.