There is no more difficulty in understanding how the branched spines of some ancient Echinoderm, which served as a defence, became developed through natural selection into tridactyle pedicellariae, than in understanding the development of the pincers of crustaceans, through slight, serviceable modifications in the ultimate and penultimate segments of a limb, which was at first used solely for locomotion.
Ez dago zailtasun handiagorik antzinako ekinodermatu batzuen arantza abartuak, defentsarako balio zutenak, pedizelario tridaktilo bihurtu zirela ulertzeko, beste hau ulertzeko baino, alegia, aldakuntza txiki eta baliagarrien bidez hasieran ibiltzeko beste ezertarako ez zen krustazeoen hanka baten azken eta azkenaurreko segmentuan pintzak garatu zirela.