The material described in the present paper was collected by Dr Rašín in 1935. It consisted of an infected ovary of Leuciscus cephalus L. from the Svitava river near Brno, and an ovary of Esox lucius from Ríčka in the vicinity of Vranovice near Brno, C.S.R. The ovaries were fixed partly with formol-Zenker solution, and partly with Gilson's fixative. The infected roes could be distinguished easily from the healthy ones by their white colour. Histological examination showed that they were infected with Microsporidia. As the material had been fixed, no polar filaments could be observed. Sections, 4μ in thickness, were stained with Heidenhain's iron haematoxylin, which once more proved to be a stain which gave the greatest contrast in preparations of Microsporidia. In addition, sections were stained with Mallory and Mann's stains, and were also subjected to Feulgen's nucleal reaction.