The white mules represent Mrs Gould, as we were reminded above. Charles Gould having surrendered the idealistic purpose of his materialist crusade, and recognized himself as a mere power-wielder equal to Hernandez, he has thereby surrendered his tie to Emily, who always represented the idealistic, humanitarian side of their San Tomé venture. He will thus never see the mules (i.e., the altruist aspect of his conquest) again.