{HEAD ~ The reflectors} comprise {TAIL ~ ruled surfaces} and are arranged to converge from entrance to exit apertures 
comprise
{ HEAD ~ The reflectors } comprise { TAIL ~ ruled surfaces } and are arranged to converge from entrance to exit apertures
HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH