SECTION 1. Subsection (a) of Section eight, of Commonwealth Act Numbered One hundred eighty-six, as amended, is further amended to read as follows:
"SEC. 8. (a) Compulsory membership insurance.&mdashAn employee whose membership in the System is compulsory shall be automatically insured on the first day of the calendar month following the month he was appointed or on the first day of the calendar month he was appointed if the date of his appointment is the first day of the month: Provided, That his medical examination, it required, has been approved by the System: And provided, further. That he has satisfactorily completed the six-months probationary period required under the new Civil Service Law before his appointment becomes permanent: And provided, finally, That the rates of premiums as prescribed in Section five of this Act shall be payable retroactively by him and his employer under such terms and conditions as the System may prescribe.