CANNIBALISM IN AMOEBA 705 



individuals and which have been erroneously interpreted as 

 cases of endogenous budding, the amoebae were studied under 

 conditions of artificial cultivation which at least differed widely 

 from the normal environment of the amoebae, is additional 

 evidence in support of this view. Until the methods of culti- 

 vating Protozoa are standardized upon the basis of a scientific 

 physical and chemical analysis of the normal environment of 

 these highly sensitive organisms, we must expect that atypical 

 and bizarre phenomena will be witnessed in cultures, and 

 that these will not only be rashly interpreted by the inexperi- 

 enced, but will also readily mislead even the most careful 

 and conscientious workers. 



Eeviewing the whole of the facts, I conclude that the hypo- 

 thesis of cannibalism explains the facts described above 

 readily and simply. It explains the variation in size of the 

 spheres and the similarity of their structure to that of the 

 amoebae which contained them. It explains also their inabihty 

 to live after extrusion, the presence of food in them while they 

 were still inside the amoebae, and the complete absence of any 

 cytological evidence of the formation of endogenous buds. 

 It affords also an explanation of the ingestion and extrusion 

 and, in some cases, of the re-ingestion of the spheres, and of the 

 remarkable occasional occurrence of several amoebae enclosing 

 one another. I am, however, unfortunately unable to throw 

 any hght upon the interesting question as to whether an amoeba 

 can digest individuals of its own species, or to determine what 

 the actual stimulus was which led these amoebae to adopt 

 temporarily the cannibalistic habit. 



In conclusion, I am pleased to have the opportunity of record- 

 ing here my indebtedness to Professor S. J. Hickson, F.R.S., 

 in whose department the work was done, for his kindly interest 

 and help, and to Miss Ann Bishop, B.Sc, and Mr. J. T. Wads- 

 worth, for many very useful suggestions and helpful criticisms. 



SUMMAEY. 



1 . This paper describes the temporary adoption by Amoeba 

 vesper tilio of cannibalistic habits. The amoebae fre- 



