Each module has a housing divided by walls into a transfer chamber at one end and {HEAD ~ a second chamber} at {TAIL ~ the other end} 
at
Each module has a housing divided by walls into a transfer chamber at one end and { HEAD ~ a second chamber } at { TAIL ~ the other end }
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL