( ( on ( migration ( of ( cells ( over ( preexisting structures ) ) ) ) ) ) ; )
(ROOT (PP (IN on) (NP (NP (NN migration)) (PP (IN of) (NP (NP (NNS cells)) (PP (IN over) (NP (VBG preexisting) (NNS structures)))))) (: ;)))
on migration of cells over preexisting structures;
(ROOT (S (NP (NNS Cells)) (VP (VBP come) (PP (IN from) (NP (VBG preexisting) (NNS cells)))) (. .)))