I was much interested in the paper on Herpetomonads in mice in the June number of Parasitology (Fantham and Porter, pp. 128–132). In 1904 or 1905 when working at trypanosomiasis at Khartoum I came across a flagellate in the peripheral blood of a gerbil (Gerbillus pygargus) which was clearly not a trypanosome and the nature of which I was unable to identify.