( Excretion ( ( ( involves filtration ) ( onto ( ( ( the coelom ) and ) ( ( ( reabsorption and ) secretion ) ( in ( the nephridium ) ) ) ) ) ) . ) )
(ROOT (S (NP (NNP Excretion)) (VP (VBZ involves) (NP (NN filtration)) (PP (IN onto) (NP (NP (DT the) (NN coelom)) (CC and) (NP (NP (NN reabsorption) (CC and) (NN secretion)) (PP (IN in) (NP (DT the) (NN nephridium))))))) (. .)))
Excretion involves filtration onto the coelom and reabsorption and secretion    in the nephridium.
(ROOT (S (NP (NP (DT The) (JJ main) (NNS functions)) (PP (IN of) (NP (NN epithelia)))) (VP (VBP are) (NP (NP (NN protection)) (PP (IN from) (NP (NP (DT the) (NN environment) (, ,) (NN coverage) (, ,) (NN secretion) (CC and) (NN excretion)) (, ,) (NP (NN absorption)) (, ,) (CC and) (NP (NN filtration)))))) (. .)))