Each of the components, including the mirrors, {TAIL ~ anode}, and cathode, must be sealed to the block to form {HEAD ~ a gas tight seal} 
Each of the components , including the mirrors , { TAIL ~ anode } , and cathode , must be sealed to the block to form { HEAD ~ a gas tight seal }
OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD