Selection of Food //? Sfentor Ccvrideus (Ehr.) 79 



had not eaten any of these latter organisms prior to the experi- 

 ment, nor had their ancestors for many generations eaten either 

 Phacus or Euglenas. 



FOOD OF STENTORS 



It is of course not always easy to determine what materials 

 actually serve as food and what do not; this is particularly difficult 

 in so minute an animal as Stentor. The application of tests for 

 food value used with higher animals is quite impracticable, 

 deciding whether certain things should be classed as food for Sten- 

 tor, the following criteria were employed: (i) Long continued 

 feeding of the substance in question must not injure the animal in 

 any way. (2) The material must decrease in quantity in passing 

 through the body, showing that some part has been absorbed. 

 These two tests w^ere applied with great care to the substances 

 which Stentor was seen to eat. Tabulated results follow. 



1 Substances eaten rather freely which do not serve as food: 



Powdered carmine Powdered india ink Powdered charcoal 



Dead yeast plants (?) Raphidium 



2 Substances eaten onl v occasionally which do not serve as food : 



Powdered glass Fine sand Powdered sulphur 



Potato starch grains Bits of detritus 



3 Substances eaten freely which serve as food: 



Small Stentors Paramecia Chlamydomonas 



Phacus triqueter Phacus longicaudns Euglena viridis 



Euglena spirogyra Euglena deses Trachelomonas hispida 



Trachelomonas volvocina Stylonychia Monostyla 



Arcella Coscinodiscus Lyngbya 



Oscillaria Peranema Chilomonas 



Hydatina Colpidium Amoeba 



Halteria Spirostomum Bacteria 



