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