Section 3. There shall be a clerk for the supreme judicial court for the county of Suffolk, and two clerks for the superior court of said county, one for civil and one for criminal business; and in each of the other counties a clerk of the courts who shall act as clerk of the supreme judicial court, of the superior court and of the county commissioners. All of said officers shall hold office for six years beginning with the first Wednesday of January following their election and until their successors are qualified.