486 J. A. DAWSON 



'medium size' which contained in the 'digestive cavity' an in- 

 fusorian of the same species but in 'another stage of development.' 

 Thirty-five years later Maupas ('88) stated that Onychodromus 

 grandis under conditions of hunger was cannibalistic, while 

 Joukowsky ('98) described the appearance, in a starved culture, 

 of a large specimen of Pleurotricha lanceolata which he believed 

 had attained its great size by eating its own relatives. Later, 

 in cultures of Onychodromus grandis, under similar conditions, 

 he saw large specimens, which, upon staining, showed within the 

 cell the nuclear structure of what he interpreted as the remains 

 of ingested animals of the same species. 



As the occurrence of giant forms was so universal in mass 

 cultures of Oxytricha hymenostoma, and as previous investi- 

 gators had only referred incidentally to this phenomenon — all 

 evidence submitted to date being largely inferential — it was 

 decided to make a detailed study of this phase of the life-history 

 of Oxytricha hymenostoma. In order, if possible, to relate these 

 phenomena to characteristic physiological changes in the life of 

 the cultures, the following study has been made: 



1. Observations on the process of swallowing. 



2. Digestion of the swallowing animals. 



3. A study of the effect of the culture medium on cannibalism. 



4. The physiological effect on the animal as shown by the 

 division rate as compared with that of the typical animals. 



1 . Observations on the process of swallowing 



The actual swallowing of one Oxytricha by another was sus- 

 pected a considerable time before it was actually seen. During 

 the experiment recorded in section 3 many instances were afforded 

 of this act, since it took place on a large scale and under the most 

 favorable conditions for observation, i.e., a large number of 

 animals in the proper state for cannibalism were confined in a 

 relatively small space. Not only has the process been witnessed 

 in the case of cannibals which had already ingested one, two, or 

 more of their fellows, but I have observed frequently the act of 

 one animal swallowing another for the first time. 



