This clause is omitted in some mss.  Various forms of the Doxology were adopted in Cyril’s time by various parties in the Church.  Thus Theodoret (Hist. Eccles. II. c. 19) relates that Leontius, Bishop of Antioch, a.d. 348–357, observing that the Clergy and the Congregation were divided into two parties, the one using the form “and to the Son, and to the Holy Ghost,” the other “through the Son, in the Holy Ghost,” used to repeat the Doxology silently, so that those who were near could hear only “world without end.” The form which was regarded as the most orthodox, and adopted in the Liturgies ran thus:  “Glory to the Father, and to the Son, and to the Holy Ghost, now and ever, and to the ages of the ages.”  See Suicer’s Thesaurus, Δοξολογία.