( ( ( The ( estrus cycle ) ) ( of ( four ( female rats ) ) ) ) ( ( was ( tracked ( -LRB- ( ( via ( vaginal ( cell sampling ) ) ) -RRB- ) ) ) ) . ) )
(ROOT (S (NP (NP (DT The) (JJ estrus) (NN cycle)) (PP (IN of) (NP (CD four) (JJ female) (NNS rats)))) (VP (VBD was) (VP (VBN tracked) (PRN (-LRB- -LRB-) (PP (IN via) (NP (JJ vaginal) (NN cell) (NN sampling))) (-RRB- -RRB-)))) (. .)))
The estrus cycle of four female rats was tracked (via vaginal cell sampling).
(ROOT (S (NP (NNS Cells)) (VP (VBP have) (NP (CD four) (NNS cycles))) (. .)))