Tex. R. Civ. P. 224
In counties not governed as to juries by the laws providing for interchangeable juries, when the parties have announced ready for trial the clerk shall write the name of each regular juror entered of record for that week on separate slips of paper, as near the same size and appearance as may be, and shall place the slips in a box and mix them well. The clerk shall draw from the box, in the presence of the court, the names of twenty-four jurors, if in the district court, or so many as there may be, if there be a less number in the box; and the names of twelve jurors if in the county court, or so many as there may be, and write the names as drawn upon two slips of paper and deliver one slip to each party to the suit or his attorney.
Tex. R. Civ. P. 224