I 1 8 S. O. MAST. 



the prey, nor is the prey paralyzed by poison injected through 

 this organ. 



4. The trichocysts function as organs of defence. They are 

 discharged in great numbers when the seizing organ becomes 

 fastened to the ectosarc. This forces the Didinium back mechan- 

 ically and frequently breaks the connection, thus setting the 

 victim free. 



5. Well fed Didinia continue to divide for some time without 

 food, becoming smaller and smaller until they are not more than 

 one tenth the size of the original one. 



6. Encysted Didinia are frequently found. The chemical com- 

 position of the solution in which they live seems to cause them 

 to encyst, rather than lack of food, as maintained by Thon. 



7. The apparent choice of food is due to the fact that the 

 seizing organ will adhere to the surface of some organisms and 

 not to that of others. The Didinia come in contact with all sorts 

 of objects in their random swimming and attempt to swallow 

 all of those to which the seizing organ will adhere. 



LITERATURE CITED. 

 Balbiani, E. G. 



1873 Observations sur le Didinium nasutum. Arch. d. Zool. Exp., Vol. 2, 



PP. 363-394- 

 Calkins, Gary N. 



1901 The protozoa. New York. 347 pp. 

 Jennings, H. S. 



1906 The Behavior of the Lower Organisms. New York. 366 pp. 

 Thon, Karel. 



1905 Ueber den feineren Bau von Didinium nasutum, O. F. M. Protisten- 

 kunde, Vols. 5-6, pp. 280-315. 



