Chang and Eng (1811-1874) were born in Siam (present-day Thailand) and brought to the United States in 1829 where they took on the American surname Bunker. As exotic 'freaks' they were exhibited throughout America. Displeased with their managers they set up on their own after a few years and toured independently through America and Europe, which brought them fame and riches. As well-off businessmen they quit touring in 1839 and settled in North Carolina. After the American Civil War they lost part of their wealth and took up touring again, signing with famed showman P.T. Barnum in 1860. They died in 1874, aged 62, leaving behind 21(!) children and two spouses.
The Dutch pitch book pictured above was published during their European tour of 1835-36. It notes that the twins had previously visited Paris, Brussels, Antwerp, Rotterdam and The Hague, before arriving "here", i.e. Amsterdam. From adverts in the Amsterdam newspaper Algemeen Handelsblad from May 31 to June 13 we gather that the twins were exhibited to the public in Amsterdam at the club 'Tecum habita', Herengracht 248, from June 3rd to June 14th, at an admission fee of 75 cents.
The portrait by Amsterdam lithographer Ruurt de Vries Jr (1813-1874) shows the twins at the age of about 25. Interestingly, it erroneously identifies them as Chang & Eng, rather than Eng & Chang. The brothers are portrayed in Western wear and one of them is holding a book, symbolizing their sophistication.
Wetenswaardige bijzonderheden omtrent de Siamesche tweeling-broeders Chang en Eng. [Amsterdam], [1836]. 8vo. [2], 6 pp. With a lithographed portrait (22 x 15 cm) by "R[uurt]. de Vries Jr.".
References: Catalogus der Bibliotheek van het Koninklijk Zoölogisch Genootschap, Natura Artis Magistra (1899), 2353; WorldCat (1 copy: Wellcome Library); cf. Algemeen Handelsblad (1836), May 31-June 13; Orser, The Lives of Chang & Eng, pp. 73-74.