In order to avail itself of the powers conferred by sections 89.010 to 89.140, such legislative body shall appoint a commission, 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 legislative body shall not hold its public hearings or take action until it has received the final report of such commission. Where a city plan commission already exists, it may be appointed as the zoning commission.