106 Regulation of Size in Unicellular Organisms 



Cannibalism is not widespread among protozoa, per- 

 haps because of the mechanical difficulties of handling 

 a portion of food equal to the individual's own bulk. 

 Cannibalism was observed among ciliates in Oxytricha 

 by Haime ('53) and J. A. Dawson ('19), in Onycho- 

 dromus by Maupas ('88) and Joukowsky ('98), in 

 Pleurotricha by Joukowsky ('98), and in Stentor by 

 Gelei ('25). Among naked rhizopods it was reported 

 by Leidy (79), Penard ('02), Jennings ('04), Lapage 

 ('22), and Ivanic ('27). 



Oxytricha. A few interesting data upon body size 

 and upon reproduction in cannibals were recorded by 

 Dawson ('19). In Oxytricha the cannibalism was re- 

 peated very often after the first victim had been in- 

 gested. Cannibalism occurred chiefly when other food 

 was not abundant; and as a result of previous under- 

 feeding both the cannibals and their victims were much 

 smaller than well-fed individuals of other cultures. 

 Cannibals which were digesting three victims at one 

 time had about twice the volume of a well-fed individ- 

 ual, but seven times the volume of the average starved 

 individual. This may be taken to indicate that the 

 cannibals were, to begin with, larger than their vic- 

 tims. Pedigrees showed that the fission rates of canni- 

 bals were raised only barely perceptibly by the acquire- 

 ment of body substance from the victims. The victims 

 were always digested like other food substances, in 

 vacuoles. Even after digestion was complete there 

 was hardly any tendency to undergo fission. Neither 

 the swelling of the body, nor the addition of living 

 substance to the body, therefore, was a stimulus to 

 reproduction. In one case Dawson observed fifteen 

 victims inside one cannibal, and measurements showed 

 a total bulk of twenty times the volume of a starved 

 individual. 



