Nicene and Post-Nicene Fathers, Ser. II, Vol. XIV:
The Canons of the Council in Trullo; Often Called The Quinisext Council.: Canon XXXIII

Canon XXXIII.

Since we know that, in the region of the Armenians, only those are appointed to the clerical orders who are of priestly descent (following in this Jewish customs); and some of those who are even untonsured are appointed to succeed cantors and readers of the divine law, we decree that henceforth it shall not be lawful for those who wish to bring any one into the clergy, to pay regard to the descent of him who is to be ordained; but let them examine whether they are worthy (according to the decrees set forth in the holy canons) to be placed on the list of the clergy, so that they may be ecclesiastically promoted, whether they are of priestly descent or not; moreover, let them not permit any one at all to read in the ambo, according to the order of those enrolled in the clergy, unless such an one have received the priestly tonsure and the canonical benediction of his own pastor; but if any one shall have been observed to act contrary to these directions, let him be cut off.

Notes.

Ancient Epitome of Canon XXXIII.

Whoever is worthy of the priesthood should be ordained whether he is sprung of a priestly line or no.  And he that has been blessed untonsured shall not read the Holy Scriptures at the ambo.

Van Espen.

Here not obscurely does the canon join the clerical tonsure received from the bishop with the office of Reader, so much so that he that has been tonsured by the bishop is thought to have received at the same time the tonsure and the order of lector.