How to use the regionmask.defined_regions.natural_earth.natural_earth_cls function in regionmask

opt = dict(
                resolution="110m",
                category="physical",
                name="land",
                title="Natural Earth: landmask 110m",
                names=["land"],
                abbrevs=["lnd"],
                numbers=[0],
                combine_coords=True,
            )

            self._land_110 = _obtain_ne(**opt)
        return self._land_110


natural_earth = natural_earth_cls()

def __init__(self):
        super(natural_earth_cls, self).__init__()

        self._countries_110 = None
        self._countries_50 = None

        self._us_states_50 = None
        self._us_states_10 = None

        self._land_110 = None