The top ply has {HEAD ~ a wall} formed therein which interlocks with the bottom ply wall to cover and close {TAIL ~ the well} 
The top ply has { HEAD ~ a wall } formed therein which interlocks with the bottom ply wall to cover and close { TAIL ~ the well }
OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL