In order to avail itself of the powers conferred by this act, the council shall appoint a commission of five citizens, to be known as the Zoning Commission, to recommend the boundaries of the various original districts and appropriate regulations to be enforced therein. Such commission shall make a preliminary report and hold public hearings thereon before submitting its final report, and such council shall not hold its public hearings or take action until it has received the final report of such commission. When an incorporated town planning commission already exists it may be appointed as the zoning commission.