For the extra, new and additional duties imposed upon the commission and the members thereof by this chapter and for the performance of duties which are and will be hereafter required of said commission and the members thereof under this chapter, each member of the commission, in addition to the compensation otherwise provided by law to be paid to him for his service as a member of the commission, shall receive $1,500.00 annually, to be paid monthly as the salaries of other officers are paid, out of the moneys of the State Treasury provided by law for payment of salaries and other expenses of the commission.