The expense fund shall be the fund from which shall be paid all costs of administering chapters 34 to 36, inclusive, of this title, and shall be paid by the departments, institutions, commissions, boards, or agencies participating in the retirement system, and on a pro rata basis of the number of employees from said departments, institutions, commissions, boards or agencies participating in the retirement system. The board shall notify the head of each department, institution, commission, board, or agency, prior to July 1st for each year of the amount required for carrying out the administration of chapters 34 to 36, inclusive, of this title and said department, institution, commission, board or agency shall be authorized and shall make available to the board for the expense fund such funds as may be necessary for the administration of the retirement system.