It is also the custom to celebrate three Masses, of which the first, according to the ancient use, commenced at midnight. As the words of the Mass show, this first Mass commemorates the eternal generation of the Son from the Father, the second commemorates His Incarnation and birth into this world, the third His birth through grace, in the hearts of sinners. The Gelasian sacramentary mentions the _trina celebratio_. The custom is one which reaches back to early Christian times. Gregory the Great mentions it in _Hom. viii._ in _Evang._ The Leonine sacramentary contains nine different formularies for Christmas, but the other western rites, including the Mozarabic, have only one Mass for the feast. The Menology of Basil Porphyrogenitus gives the flight of Mary into Egypt on the 26th December, and St Stephen only on the following day. Since the 25th December was only chosen for reasons of a more or less accidental and external character, so too the days which immediately follow—St Stephen, St John the Evangelist, and the Holy Innocents—have no real connection with Christmas, although they are of very ancient institution. The 26th December was already a special festival in the fourth century, as appears from the sermons of St Augustine (_Sermo_ 314, c. 1), though he knows nothing of the two following days. The 220th sermon, which celebrates the Holy Innocents, is spurious.[349] They appear, however, in the African Calendar of the sixth century. On the Innocents’ Day in the Middle Ages the schoolboys used to elect a bishop who was nothing more than their leader, and the ceremony was quite harmless. For this ceremony, as well as for the crib and other popular customs still practised, the reader is referred to Heuser’s elaborate articles in the _Kirchenlexikon_, iv²., 1395-1436.