1. This paper describes the temporary adoption by Amoeba vespertilio of cannibalistic habits. The amoebae frequently ingested, but in most cases failed to digest, other individuals of their own and also of other species (A. limax).
2. In some cases, an amoeba, which had ingested another, might itself then be ingested by a third amoeba; and these three might then be taken up by a fourth amoeba, so that remarkable figures, suggesting concentric fission, resulted.
3. The victims were usually ingested while they were rounded off or sluggish, and, after extrusion, usually failed to resume their activity, although most of them developed contractile vacuolos and some showed tentative amoeboid movements. A few recovered their normal activity and resumed normal life. Amoebae, after extrusion by one amoeba, were often taken up again by other amoebae.
4. In one case an Amoeba vespertilio was observed to chase and enclose an Amoeba limax, but the Amoeba limax subsequently escaped again.
5. The ingested amoebae may easily be mistaken for endogenous buds, but there is less danger of their being mistaken for parasites.
6. No trustworthy evidence was found as to the nature of the stimulus which caused the adoption of these habits, but the question is discussed.