IO o Phylum Protozoa 



examined from time to time for several weeks. In cultures containing 

 1-5 mg. of malted milk to ioo cc. of water the Lacrymaria became very 

 abundant and continued to thrive for more than 6 weeks without adding 

 anything to the cultures. 



These cultures contained Halteria and another similar organism 

 which was not identified and numerous bacteria. The Lacrymaria were 

 observed to capture Halteria, but they appeared to feed mostly on the 



other organisms. 



Bibliography 



Mast, S. O. 1911. Habits and reactions of the ciliate Lacrymaria. J. Animal 



Behav. 1:229. 



M.E. D. 



THE CULTURE OF DIDINIUM NASUTUM 



C. Dale Beers, University of North Carolina 



THE food of Didinium nasutum is restricted by the nature of its organs 

 of food capture to a limited number of relatively large ciliates. 

 Paramecium caudatum and P. aurelia are the forms that are most readily 

 and commonly ingested, though large specimens of Colpoda, Colpidium, 

 and Frontonia are sometimes eaten. Of these food organisms Para- 

 mecium caudatum is recommended as the most satisfactory. It is 

 easily cultured [See pp. 112 — 128.] and is wholly adequate to sustain 

 Didinium indefinitely. The culture of Didinium therefore resolves itself 

 into providing the animals with a non-nutrient fluid medium of suitable 

 tonicity and reaction and with an abundance of Paramecia. 



The almost complete dependence of Didinium on Paramecium as a 

 source of food means that as a rule Didinium is found in nature only 

 where Paramecium is abundant. Pools and streams that contain a con- 

 siderable amount of decaying organic matter, including preferably a small 

 amount of sewage, are suitable collecting places. Sediment, submerged 

 decaying leaves, and plant stems should be collected, as well as water 

 from the edges of the pool or stream, for more often Didinium is collected 

 in the encysted condition, the cysts lying free in the sediment or cemented 

 to submerged objects. To this material an equal volume of vigorous 

 Paramecium culture should be added, in order to activate the cysts and to 

 induce the rapid multiplication of active specimens. I have always used 

 timothy hay infusion for growing the Paramecia for Didinium cultures. 

 Cysts will usually activate in hay infusion within a day or two, excysta- 

 tion being induced by the environmental change from freshwater to 

 infusion. The presence of the Paramecia is not a prerequisite to the 

 excystation process; the same result may be obtained with old hay 

 infusion which has never contained Paramecia. 



The food supply becomes rapidly depleted in Didinium cultures, since 



