The diagnostic stages of intestinal parasites are differentiated on the basis of specific morphologic features which can be seen microscopically. Some of the parasites listed occur only infrequently or accidentally in man; but, since their diagnostic stages may be confused with those of the more common organisms, they have been included here. For example, Entamoeba polecki is rarely found in human feces; however, it closely resembles Entamoeba histolytica and Entamoeba coli, and microscopists unaware of its existence may mistake it for these species. Likewise, several helminth species of lower animals which occasionally parasitize man are included. The diagnostic stages may be misidentified. For example, Trichostrongylus (Nematode) eggs may be confused with hookworm eggs, and Hymenolepis diminuta (Cestode) eggs may be confused with Hymenolepis nana eggs.