WALTHAM, Mass., May 12 -- Thermo Instrument Systems Inc. has finished two short-form mergers. Thermo Optek Corp. and ThermoQuest Corp., subsidiaries of Thermo Instruments, will no longer have to file periodic financial and other information with the Securities and Exchange Commission by terminating the registration of their common stock under the Securities Exchange Act of 1934. The companies' common stock will no longer be listed on the American Stock Exchange. Thermo Optek shareholders will receive $15.00 per share while ThermoQuest shareholders will receive $17.00 per share in the short-form mergers.