SECTION 1. Section one of Act Numbered Three thousand and fifty, as amended by Act Numbered Thirty-one hundred, is hereby further amended to read as follows:
"SECTION 1. Beginning on the first day of April next following the date of the approval of this Act all teachers, principals, supervisors, inspectors, superintendents, and other persons employed in supervising and directing the school work of teachers in the public school service of municipalities, provinces, and the Insular Government of the Philippine Islands, whose positions are not classified as purely clerical, without regard as to status in the classified civil service of the Philippine Islands, who have on that day, or who shall have on any date thereafter, rendered at least twenty years of service as computed in section seven of this Act, and who have not been removed from the service for cause, shall be eligible for retirement on an annuity as provided in section two hereof: Provided, That teachers, principals, supervisors, inspectors, and superintendents detailed or serving in the Department of Public Instruction and engaged principally in the inspection and supervision of private schools, in accordance with Act Numbered Twenty-seven hundred and six, shall also be entitled to pension under the term and conditions herein established: Provided, further, That lecturers and other special instructors who render provisional service shall not be eligible for pension nor shall such service be counted as teaching service in computing the length of service of a teacher: And provided, finally, That the provisions of this Act shall not include persons who are not citizens of the Philippine Islands or of the United States of America, and that no person appointed from and after June first, nineteen hundred and thirty-five, shall be given retirement if, at the date of filing his or her application for retirement, he or she has not completed the age of fifty years."