{HEAD ~ The reservoir} contains a piston that divides {TAIL ~ the reservoir} into a water swellable agent chamber and an active agent chamber 
{ HEAD ~ The reservoir } contains a piston that divides { TAIL ~ the reservoir } into a water swellable agent chamber and an active agent chamber
HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH