Natura - nature
   actualia - actual entities
     Mundus Plinius - physical world
       naturalia - natural bodies
         "crystal-kingdom"
           chemical substances
             chemical compounds
               Class amides [RkE(=O)l(OH)m (l≠0; ≥1 (OH):=(NR2))]
                 1 Class primary amides [acyl-NR2]
                 2 Class secondary amides [acyl2-NR]
                 3 Class tertiary amides [acyl3-N]
                 4 Class anilides [RkE(=O)l(OH)m (l≠0; ≥1 (OH):=(NHPh))]
                 5 Class peptides [H2NCH(R)C(=O)[NHCH(R)C(=O)]nOH]