{HEAD ~ The path} through the shell wall may release {TAIL ~ a substance} contained in the shell or allow a substance to enter the shell 
{ HEAD ~ The path } through the shell wall may release { TAIL ~ a substance } contained in the shell or allow a substance to enter the shell
HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH