Career
In 1875 he became curator at the Rijksmuseum van Natuurlijke Historie (today Naturalis) in Leiden. In 1884 he followed Hermann Schlegel as director of the museum and as editor of the journal Notes from the Leyden Museum. Jentink"s main research field was the taxonomy of mammals, where he described several marsupial, bat, and rodent taxa.
In 1886 he described the guenon species Cercopithecus signatus (sometimes known as Jentink"s guenon) on the basis of one deceased specimen which was obtained by the Rijksmuseum van Natuurlijke Historie from the Diergaarde Blijdorp in Rotterdam in 1877.
The original provenance of this species is still unknown but alternatively it might be possible that it is a hybrid between the greater spot-nosed monkey and the moustached guenon. Oldfield Thomas named the Jentink"s duiker (1892) and the Jentink"s squirrel (1887) in honor of Fredericus Anna Jentink.