§ 508. Number to be selected. The commissioner of jurors shall draw at random for each term and each separate part of a term of court at which issues are triable by jury, such number of petit jurors and such number of grand jurors as he believes necessary, unless otherwise specified by order of the appellate division or by written order of the judge appointed to hold the part or term of court. Jurors shall be drawn in such manner, and serve for such period of time, as the appropriate appellate division shall prescribe by rule.