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