Johann Friedrich Theodor Müller (1821-97), better known as Fritz Müller, and also as Müller-Desterro, was a German biologist who emigrated to southern Brazil in 1852 where he lived in and near the German community of Blumenau, Santa Catarina, remaining in Brazil for the rest of his life. There he studied the natural history of the Atlantic forest south of Sao Paulo, and was an early advocate of Darwinism. Müller spent a decade teaching at a college in Desterro and in 1876 was appointed as Travelling Naturalist to the National Museum of Rio de Janeiro. This post that gave him free range to study anything that interested him throughout the Itajai region, but when the new Brazilian Republic overthrew the liberal monarchy of Dom Pedro II in 1889 and decreed that all travelling naturalists were to be based in Rio de Janeiro, Müller refused point blank and was dismissed. As a strong supporter of Charles Darwin, in 1864 he wrote Für Darwin, arguing that Darwin's theory of evolution by natural selection was correct, and that Brazilian crustaceans and their larvae could be affected by adaptations at any growth stage. Müller sent a copy to Darwin who had it privately translated for his own use. This later English translation by William Sweetland Dallas (1824-90), a British zoologist and curator of collections at the British Museum, which includes some additional material by Müller, was published in 1869 as Facts and Arguments for Darwin, the translation and its publication having been sponsored by Darwin himself. The book is illustrated thrughout.