( Nymphs ( ( use ( ( ( the tip ) ( of ( the ( abdominal ( breathing tube ) ) ) ) ) ( to ( ( introduce ( bubbles ( of air ) ) ) ( into ( these ( excreta ( to ( form spittle ) ) ) ) ) ) ) ) ) . ) )
(ROOT (S (NP (NNS Nymphs)) (VP (VBP use) (S (NP (NP (DT the) (NN tip)) (PP (IN of) (NP (DT the) (JJ abdominal) (NN breathing) (NN tube)))) (VP (TO to) (VP (VB introduce) (NP (NP (NNS bubbles)) (PP (IN of) (NP (NN air)))) (PP (IN into) (NP (DT these) (NN excreta) (S (VP (TO to) (VP (VB form) (NP (NN spittle))))))))))) (. .)))
Nymphs use the tip of the abdominal   breathing tube to introduce bubbles of air into these excreta to form spittle.
(ROOT (S (NP (DT An) (JJ underwater) (NN spider)) (VP (VBZ uses) (NP (JJ shiny) (NN air) (NN bubble) (S (VP (TO to) (VP (VP (VB breathe)) (CC and) (VP (VB keep) (ADJP (JJ alive)))))))) (. .)))