One or more of the preceding sentences incorporates text from a publication now in the public domain: Bryan, Michael (1886). "Apostool, Cornelis". In Graves, Robert Edmund (ed.). Bryan's Dictionary of Painters and Engravers (A–K). Vol. I (3rd ed.). London: George Bell & Sons.
historici.nl
(in Dutch) Michiel Jonker, "Apostool, Cornelis", Historici.nl, 2012. Retrieved 25 April 2013.