Sentence:  And he was attending that fancy-dress ball, mark you--not, like every other well-bred Englishman, as a <WSD>Pierrot</WSD>, but as Mephistopheles... / "He said that the costume of <WSD>Pierrot</WSD>, while pleasing to the eye, lacked the authority of the Mephistopheles costume." 
Meaning of the word marked with <WSD> tags:  A character from French pantomime; a buffoon in a loose white outfit; a popular choice for a masquerade costume.