the ninth century the Gregorian chant had supplanted the old Gallican chant in all the domains of the great emperor. Spain, however, did not accept the Gregorian chant until the eleventh century, during the reign of Pope Gregory VII. The inexact system of notation (neumes) in which the Gregorian antiphonary was written necessarily laid great emphasis on the oral transmission of the melodies, hence it was hardly possible to attain perfect uniformity in different countries and in different periods. Yet it is believed that the singers of the Roman school, who were subject to severe penalties for even slight infractions of the traditions of the Gregorian procedure, succeeded in preserving through the Middle Ages not only the great body of Gregorian chant but their traditional performance with a wonderful degree of purity and inviolability. But away from Rome, while the general principles of procedure were preserved intact, modifications in details undoubtedly crept in, some unconsciously and some in deference to the various national or local predilections. Thus in Gaul and the northern countries generally, the oriental style of ornamentation, retained from earlier periods in many of the Roman melodies, met with scant favor. To satisfy these sturdy and independent singers the ornate qualities were frequently softened or eliminated altogether. Additions to the original ritual music of the Gregorian service appeared about the beginning of the tenth century under the names of sequences and tropes. The sequence was a melody of hymn-like structure which derived its name from its position in the Mass, being a continuation or sequence of the Gradual and Alleluia. It had long been a custom, introduced from the East, to prolong the final vowel of the Alleluia-chant, sung between the Epistle and the Gospel, into a free melody or vocal flourish without words, called jubilation, originally a kind of ecstatic improvisation. French musicians in the ninth century added words to these melodies. They thus became separate compositions to which at first the name ‘prose’ was given, since the words adapted to the music were without meter. Later, when these compositions became thoroughly independent, texts in metrical form were written for them, the name ‘prose’ was dropped as no longer appropriate, and the new name ‘sequence’ assumed. This change in name and character is credited to the St. Gall monk, Notker Balbulus (died 912). Sequences became very popular from the eleventh to the fifteenth centuries and mediæval office-books abound in fine specimens, many of them of extreme beauty and originality. During the tenth and eleventh centuries the monastery of St. Gall remained the chief centre of activity in the composition of sequences and Notker found a multitude of followers, mainly in Germany. Quite independent of the St. Gall influence, a second centre of activity appeared at the monastery of St. Martial in Limoges, culminating in the twelfth century in Adam of St.