40 J. -MCA. KATKR AND R. D. BURROUGHS. 



figures of cysts one would think that there should be no question 

 of the presence of a cyst wall if one were there and it seems 

 doubtful that they were really cysts. 



Stolte (1922) reports that the ciliate Blepharisma encysts only 

 in the presence of abundant food, and that large food vacuoles 

 are present in those entering encystment. He also emphasizes 

 the necessity for a relatively large number of Blepharisnia in the 

 culture before encystment is possible. This conclusion con- 

 cerning a ciliate is quite in harmony with Kofoid and Swezy's for 

 dinoflagellates. 



Koffman (1924) suggests hydrogen-ion concentration as one of 

 the essential factors in producing encystment in ciliates. He 

 says: "The ciliates require ordinarily a definite Ph zone with a 

 definite optimum, for their development. Below the minimum 

 as well as above the maximum either initiates an encystment or 

 the animals are destroyed." 



In direct contradiction to the conclusions of the two preceding 

 authors, we might mention the work of Brand (1923) who con- 

 siders that, in the case of Vorticella microstoma, hunger, oxygen 

 deficiency, and gradual drying up are the principal external 

 factors for encystment. He relegates products of metabolism 

 and chemical influence in general to a position of less importance. 



Calkins (1915) found that Didinium nasutum regularly encysts 

 entirely independent of adverse environmental conditions. How- 

 ever, encystment in this ciliate may not be entirely comparable to 

 that of other forms, as a nuclear reorganization, similar to 

 endomixis, occurs during the encysted phase. Fermor (1913) 

 has described the same sort of reorganization in Stylonychia 

 pustulata. With regard to the significance of encystment in 

 Didinium Calkins says: "In addition to the casual encystment 

 resulting from adverse environmental conditions, there is another 

 form of encystment which involves more deep lying activities of 

 the protoplasm," and again, "When the process is completed and 

 the organisms emerge from their cysts they possess from live to 

 seven times the vitality, measured by the division rate of the 

 same race prior to encystment." In the face of this statement 

 it is interesting to quote Mast (1917): "there was no evidence 

 obtained indicating that conjugation or encystment has any 



