{TAIL ~ The sampler} 23 wherein the wall comprises an inner wall and an outer wall, {HEAD ~ said walls} being concentric with each other 
{ TAIL ~ The sampler } 23 wherein the wall comprises an inner wall and an outer wall , { HEAD ~ said walls } being concentric with each other
TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH