From BiblePortal Wikipedia

Services [1]

an ecclesiastical name for arrangements of the Canticles, Te Deum, Benedictus, Benedicite, Magnificat, and Nunc Dimittis, and the psalms sung by substitution for them, consisting of a succession of varied airs, partly verse and partly chorus, sung in regular choirs, of which, probably, the germ is to be found in the Ambrosian Te Deum, a succession of chants which is mentioned first by Boethius, who lived a century after Augustine. The simplified notation of this music, as used in the Salisbury and Roman breviaries, was composed by Marbecke. Tallis's service is an imitation, rather than an adaptation, of the original arrangement. Probably the first was the setting of the Venite by Caustun in the time of Henry VIII. In 1641 complaint was made of "singing the Te Deum in prose after a cathedral church way." There are two classes:

(1) full services, which have no repetitions, and are sung with an almost regular alternation by the two choirs:

(2) verse services, which have frequent repetitions, no regular alternations, and are full of verses, either solos or passages sung in slower time by a selected number of voices.