Imperium naturæ C. Linnaeus, 1758 - nature
   Mundus Plinius - physical world
     naturalia - natural bodies
       Regnum Animale C. Linnaeus, 1758 - animal kingdom see Kingdom Animalia Linnaeus, 1758
         Class Insecta Linnaeus, 1758 - insects
           Order Aptera Linnaeus, 1758
             Genus Pulex Linnaeus, 1758
               1 Pulex irritans Linnaeus, 1758 - human flea
               2 Pulex penetrans Linnaeus, 1758