All merchandise of which the collector shall take possession under the provisions relating to the time for the discharge of a vessel's cargo shall be kept with due and reasonable care at the charge and risk of the owner. (R. S., 2969.) Post entry. If any package whatever which has been so reported is wanting, and not found on board such vessel, or if the merchandise on board such vessel does not otherwise agree with the report or manifest delivered by the master of any such vessel, in every such case the master shall be liable to a penalty of five hundred dollars; except that if it is made to appear to the satisfaction of the collector, naval officer, and surveyor, or to the major part of them where those officers are established at any port, or to the satisfaction of the collector alone where neither of the others is established, or in case of trial for the penalty, to the satisfaction of the court, that no part whatever of merchandise of such vessel has been unshipped, landed, or unladen since it was taken on board, except as specified in the report or manifest, and pursuant to permits, or that the disagreement is by accident or mistake, in such case the penalty shall not be inflicted. But in all such cases the master of any vessel shall be required and shall make a post entry or addition to the report or manifest by him delivered of any and all merchandise omitted to be included and reported in such manifest; and it shall not be lawful to grant a permit to unlade any such merchandise so omitted before such post entry or addition to such report or manifest has been made. (R. S., 2887.) Returns of unlading of cargo. When the delivery of merchandise from on board of any vessel is completed, copies of the accounts or entries which have been kept or made thereof, by the officer charged with the deliveries, shall be returned to the collector of the district, and the naval officer, if any, within three days after such delivery has been completed, if at the port where such officer resides, and if at any other port as soon as the nature of the case will admit, not exceeding fifteen days. The accounts or entries to be so returned shall comprise all deliveries made pursuant to permits, and all packages or merchandise sent to the public stores; also each and every package remaining on board of such vessel for the purpose of being exported therein to a foreign port, or to some other district of the United States. (R. S., 2888.)