( ( ( The size ) ( of ( the opening ) ) ) ( ( is ( controlled ( by ( ( ( the iris ) , ) ( ( the ( colored portion ) ) ( of ( ( the eye ) ( surrounding ( the pupil ) ) ) ) ) ) ) ) ) . ) )
(ROOT (S (NP (NP (DT The) (NN size)) (PP (IN of) (NP (DT the) (NN opening)))) (VP (VBZ is) (VP (VBN controlled) (PP (IN by) (NP (NP (DT the) (NNS iris)) (, ,) (NP (NP (DT the) (VBN colored) (NN portion)) (PP (IN of) (NP (NP (DT the) (NN eye)) (VP (VBG surrounding) (NP (DT the) (NN pupil)))))))))) (. .)))
The size of the opening is controlled by the iris, the colored portion of the eye surrounding the pupil.
(ROOT (S (NP (NP (DT The) (NN opening)) (PP (IN in) (NP (NP (DT the) (NN front)) (PP (IN of) (NP (DT the) (NN eye)))))) (VP (VBZ is) (VP (VBN called) (NP (NN pupil)))) (. .)))