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