A historical ramble on hammerhead flatworms (Platyhelminthes, Tricladida, Bipaliinae)

During the early 1820s and late 1890s, several Dutch scientists (one was actually German but appointed in The Netherlands) paid attention to hammerhead land flatworms, either in the form of unpublished drawings, by collecting specimens, or by means of taxonomic publications. Most of the material concerned specimens from the former Dutch East Indies. The workers involved were Kuhl, van Hasselt, Loman, and Weber, with the latter two scientists contributing to the studies that resulted in the magnificent land planarian monograph produced in 1899 by Ludwig von Graff. The present paper sketches the historical links between all of these workers and includes previously unpublished drawings as well as a recently unearthed handwritten letter from 1890.