Mediator Dei §53

⁵³ The subsequent advances in ecclesiastical discipline for the administering of the sacraments, that of penance for example; the institution and later suppression of the catechumenate; and again, the practice of eucharistic communion under a single species, adopted in the Latin Church; these developments were assuredly responsible in no little measure for the modification of the ancient ritual in the course of time, and for the gradual introduction of new rites considered more in accord with prevailing discipline in these matters.