III. PARTICULAR MINISTRIES
The Ministry of the Instituted Acolyte and Lector
98. The acolyte is instituted to serve at the altar and to assist the priest and deacon. In particular, it is his responsibility to prepare the altar and the sacred vessels and, if it is necessary, as an extraordinary minister, to distribute the Eucharist to the faithful.[84]
In the ministry of the altar, the acolyte has his own functions (cf. nos. 187-193), which he must perform personally.
99. The lector is instituted to proclaim the readings from Sacred Scripture, with the exception of the Gospel. He may also announce the intentions for the Prayer of the Faithful and, in the absence of a psalmist, proclaim the Psalm between the readings.
In the Eucharistic Celebration, the lector has his own proper office (cf. nos. 194-198), which he must exercise personally.
Other Ministries
100. In the absence of an instituted acolyte, lay ministers may be deputed to serve at the altar and assist the priest and the deacon; they may carry the cross, the candles, the thurible, the bread, the wine, and the water, and they may also be deputed to distribute Holy Communion as extraordinary ministers.[85]
101. In the absence of an instituted lector, other laypersons may be commissioned to proclaim the readings from Sacred Scripture. They should be truly suited to perform this function and should receive careful preparation, so that the faithful by listening to the readings from the sacred texts may develop in their hearts a warm and living love for Sacred Scripture.[86]
102. The psalmist's role is to sing the Psalm or other biblical canticle that comes between the readings. To fulfill this function correctly, it is necessary that the psalmist have the ability for singing and a facility in correct pronunciation and diction.
103. Among the faithful, the schola cantorum or choir exercises its own liturgical function, ensuring that the parts proper to it, in keeping with the different types of chants, are properly carried out and fostering the active participation of the faithful through the singing.[87] What is said about the choir also applies, in accordance with the relevant norms, to other musicians, especially the organist.
104. It is fitting that there be a cantor or a choir director to lead and sustain the people's singing. When in fact there is no choir, it is up to the cantor to lead the different chants, with the people taking part.[88]
105. The following also exercise a liturgical function:
The sacristan, who carefully arranges the liturgical books, the vestments, and other things necessary in the celebration of Mass.
The commentator, who provides the faithful, when appropriate, with brief explanations and commentaries with the purpose of introducing them to the celebration and preparing them to understand it better. The commentator's remarks must be meticulously prepared and clear though brief. In performing this function the commentator stands in an appropriate place facing the faithful, but not at the ambo.
Those who take up the collection in the church.
Those who, in some places, meet the faithful at the church entrance, lead them to appropriate places, and direct processions.
106. It is appropriate, at least in cathedrals and in larger churches, to have some competent minister, that is to say a master of ceremonies, to oversee the proper planning of sacred actions and their being carried out by the sacred ministers and the lay faithful with decorum, order, and devotion.
107. The liturgical duties that are not proper to the priest or the deacon and are listed in nos. 100-106 may also be entrusted by a liturgical blessing or a temporary deputation to suitable lay persons chosen by the pastor or rector of the church.[89] All should observe the norms established by the Bishop for his diocese regarding the office of those who serve the priest at the altar.
From: GENERAL INSTRUCTION OF THE ROMAN MISSAL