Fig. 1

Original drawing of Frontonia vernalis (a-c) and F. leucas (d-g) made by Ehrenberg in 1838: part of Plate 34, Figs VII, VIII (Ehrenberg, 1838 - Atlas). In this study Ehrenberg simply reproduced the main part of drawing of F. vernalis made by himself in 1833 ([29]: p. 383, Plate III). a, b Two large green cells in which two vacuoles are depicted, but without collecting canals. Behind the first F. vernalis cell (a), there is the profile of a conjugating pair, which the Author interpreted as a dividing cell; c a much smaller green cell, in which only a single contractile vacuole is visible; d, e, f three white cells of F. leucas with one contractile vacuole each. In the left most cell (d) collecting canals of contractile vacuole are visible; g conjugating pair of F. leucas, which again was interpreted by the Author as a dividing cell. Small transparent drops spread over the cells of F. vernalis and F. leucas are, apparently, trichocysts. The image is not copyrighted due to the age of the work