Missa Virginis Mariæ In Annuntiatione Domini

Of particular interest among Merulo’s works for organ are the two Libri di toccate. In the Primo libro, the structure consists of a fugal piece framed by two toccata-like parts. In the Libro secondo, the clearly virtuosic elements of the toccata, such as quick passages and trills, tend to transmigrate within the fugal structure.
The contemplative severity of the fugue thus assumes the brilliant musical connotations typical of the toccata. In Merulo’s hands, the toccata already takes on the formal peculiarities which characterize it in its later development, especially in the alternation with the fugue, and it thus constitutes a harmonious musical edifice, albeit within the specificity of the form.
Among those genres, which most directly concern us here, the Masses reveal the composer’s great skill in handling the plain chant, with highly developed versicles enriched by embellishments and divisions.
Such a form originated from the practice of alternating the chant of the choir with an instrumental interlude from the organ.
From the earliest days of the Christian liturgy, the chant had alternated between two choirs, following the practice of antiphony.
Now the novelty lay in the fact that the organ, substituting the alternating choir, had its own liturgical personality. This practice of substituting the chant of one of the two choirs with elaborations on the organ was in turn rooted in the 14th century (the Faenza codex), and we find testimony to its use throughout the entire renaissance period.
The alternatim, as this liturgical practice was commonly called, concerned only the chant of the Ordinarium Missæ (Kyrie, Gloria, Sanctus, Agnus Dei and possibly the Credo) rather than the Proprium Missæ (Introito, Graduale, Alleluia, Offertorio and Communio, the texts of which varied), which remained the duty of the choir and was intoned on the Gregorian melody.