( ( Reptiles ( , ( ( birds and ) mammals ) ) ) ( ( are ( ( amniotes , ) ( ( the eggs ) ( of ( which ( ( ( ( are either ) ( ( ( laid or ) carried ) ( by ( the female ) ) ) ) and ) ( are ( surrounded ( by ( ( ( several membranes ) , ) ( ( some ( of which ) ) ( are impervious ) ) ) ) ) ) ) ) ) ) ) ) . ) )
(ROOT (S (NP (NNS Reptiles) (, ,) (NNS birds) (CC and) (NNS mammals)) (VP (VBP are) (NP (NP (NNS amniotes)) (, ,) (NP (NP (DT the) (NNS eggs)) (PP (IN of) (SBAR (WHNP (WDT which)) (S (VP (VP (VBP are) (RB either) (VP (VBN laid) (CC or) (VBN carried) (PP (IN by) (NP (DT the) (NN female))))) (CC and) (VP (VBP are) (VP (VBN surrounded) (PP (IN by) (NP (NP (JJ several) (NNS membranes)) (, ,) (SBAR (WHNP (NP (DT some)) (WHPP (IN of) (WHNP (WDT which)))) (S (VP (VBP are) (ADJP (JJ impervious)))))))))))))))) (. .)))
Reptiles, birds and mammals are amniotes, the eggs of which are either laid or carried by the female and are surrounded by several membranes, some of which are impervious.
(ROOT (S (SBAR (IN Because) (S (NP (PRP$ their) (NNS embryos)) (VP (VBP are) (VP (VBN surrounded) (PP (IN by) (NP (DT a) (JJ thin) (NN membrane))))))) (, ,) (NP (NNS reptiles)) (VP (VBP are) (VP (VBN considered) (NP (NNS amniotes)))) (. .)))