The Vedanta Sutras of Badarayana, Commentary by Sankara (SBE38), tr. by George Thibaut  at sacred-texts.com
61. With the (meditations on) members (of sacrificial acts) it is as with their abodes.
Are those meditations--enjoined in the three Vedas--which rest on members of sacrificial actions such as the
udgîtha to be superadded to each other, or may we proceed with regard to them as we like?--To this doubt the Sûtra replies, 'it is according to the abodes.' As the abiding-places of those meditations, viz. the Stotra and so on, are combined (for the performance of the sacrifice), so those meditations also. For a meditation is subject to what it rests on.