Section 13. The clerks of the senate and house of representatives, subject to the approval of the senate and house, respectively, may each appoint an assistant clerk and a second assistant clerk, who shall receive such salaries as may be established by the committee on rules of the senate or the committee on rules of the house, as the case may be. The assistant clerk shall, in the absence of the clerk, perform the duties of the clerk unless a temporary clerk is chosen. The second assistant clerk shall, in the absence of the clerk and the assistant clerk, perform the duties of clerk, unless a temporary clerk is chosen. Salaries established for said assistant clerks and second assistant clerks under this section shall be for the period of two years commencing January first of the year in which established. Each clerk may remove the assistant clerk and the second assistant clerk appointed by him. Each clerk may also employ such clerical assistance as may be necessary, and may expend therefor such amounts as are appropriated.