CANNIBALISM IN AMOEBA 701 



of bacteria, became voracious carnivores when they were 

 supphed with Colpiclium colpoda; and Doflein has 

 recorded a similar fact {9h). It is not surprising, therefore, that 

 an amoeba hke Amoeba v e s p e r t i 1 i o , which feeds normally 

 upon diatoms and had been kept for many years in an 

 old hay infusion in which its normal food supply must have 

 been for long scarce, and in which Paramoecium and other 

 Ciliates were present, should have turned, under the stimulus 

 of the change of environment provided by the sub-cultures, 

 to the ingesting, not only of the diatoms which developed in 

 those sub-cultures, but also of other amoebae, both of its own 

 and of other species. 



At first I was inclined to think that starvation played a part 

 in causing the amoebae to become cannibalistic. They showed, 

 however, few other signs of starvation. They exhibited normal 

 activity, they multiplied abundantly, and, beyond what was 

 probably a more marked vacuolation than is usual for the 

 species, were in no other way abnormal. They are still living 

 in the same dishes, although they have been practically 

 untouched for two years ; but they only occasionally now 

 ingest one another, and are feeding actively upon algae which 

 have developed in the cultures. 



It is, moreover, by no means certain that in 1920 they were 

 ingesting their own species alone. Though this probably 

 occurred often, in other cases a comparison of the sizes of the 

 spheres and especially of their nuclei with those of the other 

 amoebae present in the cultures (cf. supra, p. 675) suggested 

 that the small spheres were mostly ingested examples of 

 Amoeba limax. Many of the medium-sized spheres might 

 equally well have been either large individuals of A. limax 

 or small examples of A. vespertilio. 



In this connexion the interesting question arises as to 

 whether an amoeba, even if it ingest a member of its own species, 

 can digest it. I have only been able to follow, in the hving 

 object, one case of what appeared to be the digestion of the 

 ingested sphere (v. also supra, p. 686). In the stained pre- 

 parations spheres were often seen, of all sizes, which took the 



NO. 264 3 B 



