AN AMICRONUCLEATE OXYTRICHA 487 



On January 1, 1918, the following observations were made on 

 a depression-slide culture (2B, see p. 494) in which already many 

 instances of a cannibal swallowing other animals of its species 

 had been seen. One Oxytricha, apparently typical, seized a 

 smaller animal by the posterior end (10.55 p.m.). At the end of 

 five minutes its peristomial membranelles could be plainly seen, 

 vibrating in the mouth of the larger animal. At the end of 

 seven minutes (11.02) no sign of the smaller animal was visible. 

 The cannibal was carefully watched for five minutes more, 

 former experience having shown that any attempt to isolate it 

 would probably be followed by egestion of the swallowed animal. 

 The larger animal was then isolated, fixed and stained. Exami- 

 nation of the stained specimen showed the body of the ingested 

 animal somewhat rounded off but still intact, with such structures 

 as the peristomial membranelles and anal cirri distinctly visible. 

 Figure 9 shows a cannibal on which a similar observation had 

 been made, but which had some time previously swallowed another 

 animal. It will be noted in this case that the peristomial mem- 

 branelles of the ingested animal can still be seen as well as the 

 macronuclei. The posterior macronucleus of the swallowed 

 animal lies just under the anterior end of the posterior nucleus 

 of the cannibal. The remains of the animal swallowed previously 

 are visible as a large faintly staining vacuole in an advanced 

 stage of digestion. Figure 11 shows a cannibal which has just 

 swallowed a fused pair of smaller animals, the macronuclei of 

 which are distinctly visible. 



Many cases have been noted of apparently successful attempts 

 to swallow followed by the disgorging of the swallowed animal, 

 which usually seemed none the worse for the experience. Figure 

 13 shows such a cannibal which had already swallowed five ani- 

 mals and had succeeded in taking in the Oxytricha shown in 

 figure 14, but during the operation of isolation the smaller 

 animal was disgorged and swam about actively. A comparison 

 of the size of these animals shows what was invariably found in 

 all observations on swallowing, i.e., the ingested animal, when it 

 is the first animal to be swallowed by a cannibal, is always 

 smaller than the latter. When a culture is in a state favorable 



