After performing the duties hereinbefore specified, the powers and duties of the assessors, aforesaid, shall cease and determine; and the auditor general and state treasurer shall annually, in the month of January, appoint said assessors, and assign their respective districts, or counties; and the assessors shall make return to the commissioners aforesaid, within sixty days after their appointment, and be removable at the pleasure of the auditor general and state treasurer.
72 P.S. § 1934