688 GEOFFKEY LAPAGE 



Discussion. 



Three main possibilities suggested themselves as explana- 

 tions of the observations just described. 



First, the spheres may have been parasites ; secondly, they 

 may have represented some form of reproduction, such as 

 endogenous budding ; thirdly, they may indeed have been 

 food bodies, the amoebae having ingested other amoebae 

 of the same or other species. On this last view, the phenomena 

 were those of ' cannibalism ". As the title of the paper shows, 

 I believe this last to be the correct interpretation. 



In order to give my reasons for this conclusion, it will be 

 necessary to discuss these three views in turn. 



(1) The Parasite Hypothesis. 



At first this view seemed very probable. The spheres 

 resembled, at first sight, organisms like the Suctorian Sphaero- 

 phrya, which is so common a parasite of Ciliata in cultures. 

 Closer examination of them quickly proved, however, that not 

 only did the spheres never show any structure resembling 

 tentacles but also that no Suctoria were ever present in the 

 cultures. Further, the nucleus of Sphaerophrya is not vesicular. 

 The spheres, in fact, did not show any single feature by which 

 they could be classified as Suctoria. 



Prandtl (22) has described a Thecamoebidan, AUogromia, 

 which became parasitic upon Amoeba proteus, Arcella, 

 Nuclearia, and Paramoeeium in order to accomplish its sexual 

 cycle in their interior. Tliis organism, however, does not in 

 any way resemble the spheres described above. Not only 

 were no shelled Rhizopods ever seen in any of my cultures, 

 but the structure of AUogromia, its possession of chromidia 

 and the changes which it undergoes in its host, together %nth 

 the fact that it is capable of reducing its host's vitality, definitely 

 exclude any possibility that the spheres were parasites of this 

 nature. 



Buck (1) has described, under the name Phonergates 

 vorax, another shelled Ehizopod, identical, according to 



