The distribution of fresh-water protozoan species on an artificial uniform substrate was studied in plastic troughs with continuous flow of unfiltered lake water. Ten areas were sampled at the same time in each trough and the diversity of species per area determined. Estimates were made of the density as well, but since some species were too delicate to preserve without destroying certain taxonomic characters the primary emphasis was placed on the diversity of species. No patterns were evident which suggested anything other than a random distribution of both species and individuals within each system. The situation appears conceptually similar to that originally pointed out by G. Evelyn Hutchinson in ’The Paradox of the Plankton’ in which he notes the difficulty of applying the niche concept to the multi-specific association of autotrophic phytoplankton in the freely circulating upper water of lakes and oceans.