def iter_descendants(self, ontology, iri, size=None, sleep=None):
        """Iterates over the descendants of a given term

        :param str ontology: The name of the ontology
        :param str iri: The IRI of a term
        :param int size: The size of each page. Defaults to 500, which is the maximum allowed by the EBI.
        :param int sleep: The amount of time to sleep between pages. Defaults to 0 seconds.
        :rtype: iter[dict]
        """
        url = self.ontology_term_descendants_fmt.format(ontology=ontology, iri=iri)
        log.info('getting %s', url)
        for term in self._iter_terms_helper(url, size=size, sleep=sleep):
            yield term