Mass. Gen. Laws ch. 277 § 3A
On the day when veniremen are summoned pursuant to section one, section two, section two A, section two B, section two C, section two D, section two E or section two F to attend court for the formation of a grand jury, the clerk of courts in any county, or in Suffolk county the clerk of the superior court for criminal business, shall cause the name of each person so summoned, and who appears and who has not been excused or set aside, to be written on separate ballots, substantially of uniform size, and shall cause such ballots to be placed in a box provided therefor. The clerk in open court, after shaking the ballots thoroughly, shall draw them out in succession until he has drawn the names of twenty-three grand jurors.
Mass. Gen. Laws ch. 277, § 3A