Abstract
1. A description of the morphology and life history (excluding metacystic development) ofEntamoeba murisis given.2. The descriptions of species of amoebae found in rats (Rattus norvegicus and R. rattus) and mice (Mus musculus) by previous authors are critically discussed, and it is concluded that one species,Entamoeba muris, is present.3 Experiments on cross-infection of rats and mice withE. murisare described, together with observations on the course of these infections.4. The transference of an amoeba morphologically similar toE. murisfromCricetus auratusto rats and mice is described.5. An account is given of unsuccessful attempts to establish an infection ofEntamoeba coliin rats and mice.6. Observations on the incidence and hostrestriction ofE. murisare discussed.7. The affinities ofE. coliandE. murisare discussed and it is concluded that, although E. muris resemblesE. colimorphologically, it differs fromE. colion physiological grounds.
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