a sphering on {TAIL ~ the fly channel} in {HEAD ~ fluid communication} with the second one of the reagent storage reservoirs; and 
a sphering on { TAIL ~ the fly channel } in { HEAD ~ fluid communication } with the second one of the reagent storage reservoirs ; and
OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH