l6 THE BIOLOGY OF STENTOR 



therefore a hunger for their own type of protoplasm because of 

 some deficiency which has developed. Also it seems unreasonable 

 to suppose they could correct this lack by ingesting animals in the 

 same culture, therefore subject to the same deprivations. Likewise 

 we have to question Johnson's plausible and attractive suggestion 

 that cannibahsm should help the species to survive a period of 

 scarcity, although an ** ecological" study and sampling of un- 

 disturbed cultures might demonstrate this to be the case. Gelei 

 thought cannibalism a racial trait in coeruleus but its occurrence 

 without exception in a wide selection of stocks is against this 

 interpretation. 



Stentors ingest only free-swimming stentors because the prey 

 is taken in by the attenuated tail end. By agitating the culture jar 

 to set animals loose, Gelei was able to increase the incidence of 

 cannibalism from about 1.5% to 4.6%, but never more. The 

 posterior point of the animal to be eaten is drawn deep into the 

 gullet where it is held in spite of the prey's rotating and attempting 

 to escape. In fact, the victims may usually manage to escape and 

 I believe no one has actually observed the swallowing, but this 

 may be due to disturbance by bright illumination under the micro- 

 scope. As mentioned, the rim of the oral pouch shows contractions 

 that may even bite off the posterior end of the prey. Ingested 

 animals are usually smaller than the predator, yet Gelei stated that 

 cannibals may swallow animals larger than themselves. Once inside, 

 the victim is not surrounded by a food vacuole at first; therefore 

 it remains alive and actively rotating for perhaps the better part 

 of a day, during which it can be released and always, in my experi- 

 ence, will recover. If not released the prey is eventually surrounded 

 by a membrane and enclosed as a food vacuole within which it 

 stops moving, dies, and becomes wrinkled within an hour. Stentors 

 will also eat individuals of a diflFerent species of the same genus. 

 I have frequently found polymorphus ingested by larger coeruleus. 



There is no doubt that stentors, like other cannibal ciliates, 

 can digest their own kind. As Gelei described the process, coagula- 

 tion is the first sign of digestion and the corpse becomes friable. 

 Fat spherules then appear in "astonishing" numbers; this could 

 be due to the coalescence of pre-existing lipoid droplets which are 

 very tiny and not easily seen. The nucleus is digested, its nodes 

 falling apart and becoming progressively smaller and more weakly 



