268 



BIOLOGY OF THE PROTOZOA 



accumulate until thousands of individuals are present. The food 

 medium is not replenished and such mass cultures are watched daily 

 until the individuals die. After five or six days conjugations will 



Fig. 137. — Vitality graphs showing the limited period of encystment (between 

 the two irregular vertical single lines), and the periods at which conjugation begins 

 (double line) in ten different series of Uroleptus mobilis. (Original.) 



take place provided the organisms are mature; if they are not 

 mature encystment takes place and it frequently happens that 

 thousands of cysts are present in one container. From the records 



