In the 12th century with increased veneration of the Eucharist, ways of showing the Eucharist increased. The "reserved sacrament," bread left over after distribution to worshippers at Mass, was kept in special receptacles. One of these was formed in the shape of a dove.  The body of the dove could open to receive the wafer. Many such doves have survived as part of church treasuries or museums.  The dove shape was an allusion to the Holy Spirit, the Third Person of the Blessed Trinity that was often depicted in the form of a dove.  (Viollet-le-Duc, Mobilier 1:249: Cluny Museum, Paris, 12th century) back to "worship"