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