ellipse: function(parent, cx, cy, rx, ry, settings) {
        var args = this._args(arguments, ['cx', 'cy', 'rx', 'ry']);
        return this._makeNode(args.parent, 'ellipse', $.extend(
            {cx: args.cx, cy: args.cy, rx: args.rx, ry: args.ry}, args.settings || {}));
    },