488 J. A. DAWSON 



for cannibalism, there has already taken place a rapid increase 

 in the number of organisms in the culture. Consequently, the 

 mean size of such animals has been found to be slightly less than 

 that of the average normal animal. Among these animals which 

 are below average size considerable variation in size occurs and, 

 although the stimulus calling forth the swallowing reaction is 

 present in most of the forms in the culture, the actual swallow- 

 ing is only successfully accomplished when a relatively large 

 Oxytricha attempts to swallow a smaller one. 



Cannibalism has been invariably found to occur, throughout 

 the whole course of the study, at the time when numerous pairs 

 are present, attached in the manner so strikingly suggestive of 

 the phenomenon of conjugation. Thus, cannibalism may be 

 interpreted, in a way, as an abortive attempt at conjugation, 

 since it occurs when the organisms are in the physical condition 

 always found in conjugating animals. When the protoplasm of 

 the animals studied in this work is in the 'miscible' condition 

 and individuals happen to unite by the anterior ends, they fuse, 

 and usually remain fused until death occurs. If the anterior end 

 of one animal happens to come in contact with the posterior 

 end of another, swallowing may take place. 



It has happened that cannibals have been found whose length 

 was less than that of the average length of the typical animal. 

 The most striking increase is in the breadth of the animal — the 

 effect being comparable to that obtained by the full inflation of 

 an ordinary rubber hot-water bottle. In appearance the can- 

 nibal is much darker than the typical single animal, and when 

 several animals have been ingested the dorsal surface often pre- 

 sents a knobby appearance where the pellicle is bulged out by 

 the contained bodies. The pellicle in such a case is stretched 

 almost to the breaking point and considerable care has to be 

 used in handling these cannibals with the capillary pipette to 

 avoid loss of the specimen by bursting. 



Table 1 gives a series of measurements made on various 

 cannibals. 



It will be noted from a study of the above table that although 

 animals at the inception of the process of cannibalism have a 



