Mo. Rev. Stat. § 86.147

The annuity reserve fund shall be the fund from which shall be paid all annuities and all benefits in lieu of annuities payable as provided in sections 86.010 to 86.193. Should a beneficiary retired on account of disability be restored to active service and again become a member of the retirement system, his annuity reserve shall be transferred from the annuity reserve fund to the annuity savings fund and credited to his individual account therein.