In addition to reserves for unearned premiums and losses, as to mortgage guaranty insurance transacted by it an insurer shall establish and maintain a contingency reserve out of net premiums (gross premiums less premiums returned to policy holders) remaining after establishment of the unearned premium reserve. To the contingency reserve the insurer shall contribute an amount equal to fifty per cent (50%) of such remaining premiums. The annual contributions to the contingency reserve made during each calendar year shall be maintained for a period of one hundred twenty (120) months; except that in any year in which incurred losses of the insurer under mortgage guaranty insurance policies exceed thirty-five per cent (35%) of the corresponding earned premiums, the insurer may withdraw from the contingency reserve an amount equal to not more than the amount of such excess.