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