{TAIL ~ The body portion} 15a is formed into a generally circular columnar shape, and is provided at its upper portion with {HEAD ~ a gas exit} 15b 
{ TAIL ~ The body portion } 15a is formed into a generally circular columnar shape , and is provided at its upper portion with { HEAD ~ a gas exit } 15b
TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH