Contributions to and payments from the pension accumulation fund shall be as follows: On account of each member there shall be paid annually into the pension accumulation fund by the said cities an amount equal to a certain percentage of the earnable compensation of the member to be known as “the normal contribution” and an additional amount equal to a percentage of his earnable compensation to be known as “the accrued liability contribution”. The rates percent of such contributions shall be fixed on the basis of the liabilities of the retirement system as shown by actuarial valuations. Until the first valuation the normal contribution shall be five and thirty-one one-hundredths percent and the accrued liability contribution four and forty-nine one-hundredths percent of the earnable compensation of all members.