One of the electrodes includes {TAIL ~ openings} for allowing the vapor to enter {HEAD ~ the space} 
One of the electrodes includes { TAIL ~ openings } for allowing the vapor to enter { HEAD ~ the space }
OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD