ENCYSTMENT OF DIDINIUM NASUTUM. HI 



change in the quality of the food. However this may be, encyst- 

 ment occurs freely in the culture media which are very favorable 

 for growth and reproduction of paramecia. The maximum was 

 found in cultures six days old, when the paramecia were very 

 abundant and vigorous. Whether or not fission rate was at a 

 maximum at this time was. however, not ascertained. 



SUMMARY. 



1. Didinia encyst most readily at a temperature of 25-3O, 

 which is also the optimum temperature for growth and fission. 



2. They do not encyst in temperature so low or so high that it 

 is injurious. They do not encyst at all below 16 and rarely 

 above 39. 



3. They encyst more freely in cultures supplied with food than 

 in those without food, but this is probably due to greater increase 

 in numbers, resulting in greater accumulation of waste material in 

 the one than in the other. 



4. They encyst most readily in culture media, which are probably 

 most favorable for growth and reproduction of the paramecia on 

 which they feed. 



5. Encystment serves as protection against unfavorable condi- 

 tions in reference to food and temperature, but such conditions do 

 not facilitate encystment. 



6. Encystment is probably induced by the accumulation of ex- 

 cretory waste material. 



LITERATURE. 



Brauer, August. 



'94 Uber die Encystirung von Actionosphaerium Eichhorni, Ehrbg. Zeit. 



fur Wiss. Zool., Bd. 58, S. 192-219. 

 Baker. 



'71 Quoted by Ritzema Bos (1886). Biol. Centralbl., Bd. 7, S. 650. 

 Bodine, J. H. 



'23 Tourn. Exp. Zool. 

 Biitschli, C. 



'89 Encystirung (Ruckbildungsvorgange, Condensation, Contr. vacuolen). 

 Bronn's Klassen Ord. d. Thierreichs, III. Abth. Infusoria. S. 1652- 

 1654. 

 Calkins, G. A. 



'06 The Protozoan Life Cycle. BIOL. BULL., Vol. n, pp. 229-244. 

 '10 The Protozoa. New York. 



